EOS

In recent years, the breakdown of the “polar vortex” has often made the evening news, to explain unusually cold snaps over North America. The vortex is a climatological feature of the atmospheric circulation that is associated with the temperature gradient, or difference, between the tropics (low latitudes) and the pole (high latitudes): in winter, when this temperature difference is largest, it makes for a strong mid-latitude jet, of winds blowing west to east, which corral the cold air near the pole.

Warming of the atmosphere can affect the jet in two contrasting ways, hence the reference to a “tug-of-war”. As the tropics warm and expand, they push the jet poleward. But because the Arctic is warming more than the rest of the hemisphere, a phenomenon known as “Arctic amplification”, the equator-to-pole temperature difference is overall reduced, weakening the jet.

Up until now, modelling studies were marred by a lack in consistency, both in terms of their experimental design and the responses identified. Peings et al. [2019] explore an important factor resolving this lack of consistency, which typically results in the “tug-of-war”: the polar stratosphere. With this key component appropriately represented in a climate model, they find that in fact, in wintertime, upper tropospheric tropical warming and Arctic amplification do not oppose each other, but rather, concur to weaken the jet.

Citation: Peings, Y., Cattiaux, J., & Magnusdottir, G. [2019]. The polar stratosphere as an arbiter of the projected tropical versus polar tug of war. Geophysical Research Letters, 46, 9261– 9270. https://doi.org/10.1029/2019GL082463

—Alessandra Giannini, Editor, Geophysical Research Letters

“Nature is angry,” United Nations Secretary-General António Guterres warned at the start of the 2019 Climate Action Summit on 23 September. “Our warming Earth is issuing a chilling cry: ‘Stop.’ If we don’t urgently change our ways of life, we jeopardize life itself.”

The conference “is not a climate negotiation summit, because we don’t negotiate with nature. This is a climate action summit,” Guterres said. Limiting warming to 1.5°C above preindustrial levels is still possible, if there are “fundamental transformations” in all aspects of society.

The summit did come through with a number of announced actions and initiatives, though some environmentalists, political leaders, and scientists questioned whether those announcements are sufficient to meet the challenges posed by climate change.

The summit focused on nine interdependent tracks: mitigation, resilience and adaptation, infrastructure, energy transition, industry transition, climate finance and carbon pricing, social and political drivers, public mobilization, and nature-based climate change solutions.

Among the announcements by governments, businesses, finance groups, and nongovernmental organizations at the summit, 59 nations signaled that they intend to submit enhanced climate action plans under the Paris climate accord; companies with a combined market capitalization topping US$2.3 trillion pledged to take actions to align their businesses with science-based climate targets; the Powering Past Coal Alliance expanded to include 30 countries among other parties that are committed to stop building new coal power plants in 2020; and the shipping industry announced that it is launching a Getting to Zero Coalition to reduce greenhouse gas emissions by at least 50% by 2050.

Other announcements included the launch of the High Ambition Coalition for Nature, whose goal is to conserve 30% of Earth’s lands and oceans by 2030; a pledge by the Zero Carbon Buildings for All initiative to work to make new buildings 100% net zero carbon by 2030; and efforts by the Central African Forest Initiative to maintain the forest cover of that region.

More Measures Needed

Despite those and other announcements, Guterres was among those calling for much more action to stop what he referred to as “the climate crisis.” Those actions, he said, should include, for instance, much more progress on carbon pricing and no new coal power plants being built after 2020.

Guterres spoke about his granddaughters. “I refuse to be an accomplice in the destruction of their home and only home. I will not be a silent witness to the crime of dooming our present and destroying their right to a sustainable future. It is my obligation—our obligation—to do everything to stop the climate crisis before it stops us.”

Others, too, expressed their outrage about climate change, including Swedish climate activist Greta Thunberg, 16, who addressed world leaders and summit delegates near the beginning of the meeting.“The eyes of all future generations are upon you. And if you choose to fail us, I say, we will never forgive you.”

“My message is that we’ll be watching you,” Thunberg said in an impassioned and emotional speech. “This is all wrong. I shouldn’t be up here. I should be back in school on the other side of the ocean. Yet you all come to us young people for hope. How dare you. You have stolen my dreams and my childhood with your empty words.”

Thunberg added, “We are in the beginning of a mass extinction, and all you can talk about is money and fairy tales of eternal economic growth. How dare you.”

Addressing the audience, she said, “You are failing us, but the young people are starting to understand your betrayal. The eyes of all future generations are upon you. And if you choose to fail us, I say, we will never forgive you. We will not let you get away with this. Right here, right now is where we draw the line. The world is waking up. And change is coming whether you like it or not.”

A Possible Groundswell Building for More Action

Several scientists involved with major initiatives to protect the environment and curb climate change told Eos that the world needs to act with much greater urgency than the initiatives and announcements made at the summit indicate.

Lee White, Gabon’s minister for forests, sea, the environment and climate plan, said that he sees some hope for progress through a number of measures discussed at the summit, including the Central African Forest Initiative.“If the retirement homes and the golf courses in Florida start going under water, then maybe the world will come in with a stronger reaction.”

However, White told Eos that major required actions to deal more effectively with climate change may not take place until more people in the developed world understand that they are personally affected by, and suffering from, climate change.

“I don’t think some of these [fossil fuel] lobbies are going to accept climate change until more and more people in the developed world are dying. People in Africa are dying already. It’s a life and death scenario for people in the Sahara,” White said. “If the retirement homes and the golf courses in Florida start going under water, then maybe the world will come in with a stronger reaction. It’s tragic to say it: Not enough people in developed countries are suffering from climate change.”

White said he doesn’t think that this conference will make a landmark change, but with the global youth protests, “we are maybe starting to see a groundswell that might push politicians to do more.”

A Call for More Scientists to Speak Up

Marine biologist Enric Sala, who is a coauthor of a paper that called for conservation goals included in the initiative of the High Ambition Coalition for Nature, also said that youth activists deserve a lot of credit for pushing the climate change issue. “Thank God for them. It’s so inspiring,” he said.

Sala, an explorer in residence with the National Geographic Society, urged more scientists to speak up and not “self-censor” themselves. “You’re not just a scientist, you’re not a machine, you’re a citizen, and you should have values. Don’t be afraid to say what the science is telling you. Be up-front about the challenge of doing the science and the inherent uncertainty, but don’t self-censor.”“We don’t yet see what we need from the major actors, and that’s got to happen.”

He added that scientists “have a huge privilege to be able to do what they love, but they have a huge responsibility by showing the truth.”

David Waskow, director of the World Resources Institute’s (WRI) International Climate Initiative, told Eos that President Donald Trump’s failure to participate in the climate summit, aside from a brief visit while attending a religious freedom event that same day at the United Nations, “is an affront to those who are working on this issue.” He said it was a particular affront to youth who say that they are scared about their future and are demanding action.

Waskow said that some significant measures were announced and advanced at the summit but they don’t go far enough and that major greenhouse gas–emitting countries need to do much more.

“There’s enormous energy in the streets, there’s a lot of energy among cities and many, not all, obviously, businesses. And a lot of vulnerable countries are really ready to take strong action,” he said. “But we don’t yet see what we need from the major actors, and that’s got to happen.”

—Randy Showstack (@RandyShowstack), Staff Writer

AGU’s global community of Earth and space scientists has contributed research and expertise to our understanding of—and solutions for—climate change, natural hazards, and their related impacts on people. Climate change, the increasing severity of extreme weather, and resulting floods are health and economic crises that we cannot ignore.

To highlight the role that science plays to help address and mitigate issues such as flooding in communities across the United States, AGU released a report today titled Surging Waters: Science Empowering Communities in the Face of Flooding. This report, reviewed by leading experts, demonstrates how science is integral to solutions that will mitigate destructive impacts on people and property in the future.

Surging Waters has been released at a crucial time for our society. Floods are the costliest, most frequent type of disaster in the United States, accounting for hundreds of deaths and billions of dollars in economic losses every year. Hurricanes cost the U.S. economy an estimated $54 billion annually in damages and storm-related flooding. Flash flooding along rivers and streams is the second leading cause of death in the nation from extreme weather. Coastal flooding tied to rising sea levels is increasing and, even with clear skies on sunny days, puts communities and key military installations in jeopardy.

An estimated 40 million Americans have a 25% chance that their home will flood before they can pay off a 30-year mortgage.No state in the United States is spared the impact of flooding. In fact, an estimated 40 million Americans have a 25% chance that their home will flood before they can pay off a 30-year mortgage. To illustrate the repercussions local communities face, Surging Waters highlights three types of flooding—flooding due to hurricanes, floods in the central United States, and coastal flooding—through stories and interviews with residents and scientists working in Houston, Texas; De Soto, Mo.; and the Hampton Roads area in Virginia.

Just in time for National Preparedness Month, Surging Waters closes with recommendations to build a solid foundation for a strong, more sustainable future. Scientific collaboration, community collaboration, and financial support for science can help address the complex challenges posed by flooding and extreme weather nationwide and across our borders. Science and scientists are key elements of these solutions, but they need economic support from federal and local governments, and in turn, they must be relevant to, accessible to, and engaged with communities.

The key to solutions will be to

empower communities to make informed decisions about their future empower scientists to conduct robust scientific research and data collection about flooding and its related issues prioritize partnerships that foster collaboration, knowledge sharing, and better communication among scientists who study both the physical world and human behavior and between scientists and communities

Over the next year, AGU will conduct outreach to communities, organizations, science centers, and policy makers who can help follow through on these recommendations. In addition to the report, we have created a number of engaging multimedia resources, from state fact sheets and resources, to a fact sheet on the connection between flooding and climate change, to videos featuring local scientists and residents affected by flooding. By early October, AGU will have a Spanish translation of the full report and the climate fact sheet.

I encourage everyone to visit the Science is Essential website to download the full report and consider conducting your own outreach around the issues raised.I encourage AGU members, members of the broader scientific community, and members of the public to visit Science Is Essential to download the full report and consider conducting your own outreach around the issues raised. On that site, you can also contact your policy makers and urge them to support sustained funding for crucial federal scientific research. I also hope AGU members will consider volunteering for Thriving Earth Exchange projects in their local areas. Some Thriving Earth Exchange projects are highlighted in Surging Waters, and the community-based solutions have been a game changer in addressing climate change, natural hazards, and natural resource challenges.

Scientists are on the front lines of protecting America’s public safety, health, and economy. Ensuring that their work can continue will inspire readiness, empower communities to make informed decisions about their future, and build a more resilient society for us all.

—Chris McEntee (agu_execdirector@agu.org), Executive Director/CEO, AGU

Model hierarchies have been fundamental for our understanding of the large-scale circulation of Earth’s atmosphere. They have played a critical role in informing our ability to simulate natural variability, testing our predictive skill, and investigating how the climate will respond to external forcing, particularly increased greenhouse gas concentrations.

A recent paper in Reviews of Geophysics explores the broad use of idealized atmospheric models to understand the large-scale circulation, starting with the most simple models that form the basis of our understanding of the atmosphere and how they connect to the comprehensive models used for climate prediction through model hierarchies.

Here, the two lead authors give an overview of what a climate model hierarchy is, why we use simple climate models, and how these models have helped us to understand the large-scale circulation of the atmosphere.

What is a climate model hierarchy?

Climate model hierarchies can be thought of as a ladder connecting our complex climate models to our physical understanding of nature. Credit: Dejan Krsmanovic (CC BY 2.0)

You can think of a climate model hierarchy as a ladder connecting our understanding of basic physical principles to the Earth system in all its complexity.

At the base are conceptual models, our simplest ways of describing the processes and laws governing the climate system. An example would be a zero-dimensional energy balance model of the atmosphere and its response to increase greenhouse gas concentrations, as first developed by Arrhenius in 1896.

At the top are our most advanced climate prediction models developed to inform the Intergovernmental Panel on Climate Change (IPCC). These state-of-the-art models are continually evolving as they increase in realism (representing additional physical processes) and resolution (allowing a more scales).

A model hierarchy is a series of models that connect our simple conceptual models, based on our conceptual understanding, to the most advanced prediction models, and are constructed by incrementally adding key processes and scales, one by one.

Just as a tall ladder with only a few steps at the top isn’t very useful if you are standing on the ground, our most advanced models need to be connected to be grounded in our conceptual understanding, validated, and improved.

Why do we use simple climate models?

Since the climate is complex, our climate models also need to be complex … but there needs to be some simplification to build understanding.Since the climate is complex, our climate models also need to be complex, but trying to model all the details of our climate system can impede understanding. There needs to be some simplification to build understanding.

When we strip back models to their most fundamental components, we can isolate and understand their behavior and identify “model biases” that need to be fixed. Perhaps a model is missing a key process. Perhaps a newly added process is not properly represented or coupled with the rest of the climate system. Maybe there are more fundamental problems lurking beneath in processes we thought we fully understood. We can then add in complexity incrementally to build up to a more realistic model.

In addition to fixing model biases, another aim of simple model studies is to understand a process, feedback, or mechanism. The task then becomes how to relate understanding gained from simple models back to the real climate; this is where a model hierarchy becomes essential.

How are models organized into hierarchies?

While this appears to be a simple question, there is not a simple answer. How you organize a hierarchy depends on the research questions you are exploring.

There are, however, a number of models which have been studied in broad contexts, thus establishing them as ‘benchmarks’ in our understanding. For example, in terms of the general circulation of the atmosphere, one benchmark is the Held and Suarez [1994] model, which assumes the atmosphere is dry, i.e., there is no representation of moist processes like clouds and rainfall.

Aquaplanets are a commonly used idealized model. These models have a surface that is entirely covered by ocean. Credit: Vladimir Kud (CC BY 2.0)

To begin to incorporate the role of moisture in heat transport – but not on radiative transfer – the idealized aquaplanet model of Frierson [2007] simulates a moist atmosphere with a series of simplifying assumptions that decouple moisture from radiative transfer. To allow moisture to interact with radiation (both through water vapor and clouds), we then use a conventional aquaplanet model – a full atmospheric model coupled to a simple slab ocean, or with fixed sea surface temperatures.

These models are just one illustration of a model hierarchy. They differ in their treatment of “atmospheric physics”, allowing us to incrementally explore the coupling between diabatic processes (radiation and convection) and the large-scale atmospheric circulation.

In our review, we describe three principles that help organize models into hierarchies. First, a dynamical hierarchy can be used to explore the fundamental equations used to predict the atmospheric flow. Second, a process hierarchy allows us to incorporate processes that drive the atmospheric circulation; the models described above fit into this category. Finally, we can organize a hierarchy based on the scales and domain size to explore the time and space dependence of the system.

How have model hierarchies improved our understanding of atmospheric circulation?

Model hierarchies allow us to make progress in addressing key research areas.There is a rich history of dry idealized modeling studies applied to the mid-latitudes and stratosphere that dates back to the 1960s. But idealized moist models have grown in popularity over the last 15 years and are a promising approach for making progress at the frontiers of climate research, such as the coupling of clouds and circulation.

“Dry” models of the climate, i.e., atmospheric models that do not include a representation of moist processes, have enabled our understanding of eddy feedbacks, jet streams, wave mean flow interactions, stratospheric transport and the tropical Walker circulation. Meanwhile, idealized moist models have been influential in understanding the tropical circulation and feedbacks between the convection, clouds, and circulation.

Model hierarchies also allow us to make progress in addressing key research areas, such as convective organization, cloud feedbacks, Earth’s equilibrium climate sensitivity, and the Madden-Julian Oscillation.

—Penelope Maher (p.maher@exeter.ac.uk;  0000-0001-8513-8700), University of Exeter, UK; and Edwin P. Gerber ( 0000-0002-6010-6638), New York University, USA

Mike Meyer recently returned to investigating 83 mysterious objects from his past.

Collected while sifting through fossilized clams in a Florida quarry in 2006, the identities of these microscopic objects were unknown for more than a decade. Many of the glassy spheres, about 200 micrometers in diameter, are translucent, and others have frosty surfaces. Some have bumps or cracks on their surfaces, likely caused by the abrasive action of sand grains, said Meyer, an Earth systems scientist at Harrisburg University in Pennsylvania.

More than a decade later, Meyer and coauthors of a study published in Meteoritics and Planetary Science analyzed the physical characteristics and elemental compositions of the mysterious microspherules. The team concluded that the curious objects “are likely microtektites or a closely related type of material.”

Microtektites are tiny bodies of natural glass formed from terrestrial debris ejected during meteorite impacts.

Meyer estimates the objects to be 1 to 2 million years old on the basis of the current consensus on the age of the shell beds where they were found. However, the beads could have been transported from elsewhere before they were enclosed in the shells, introducing the possibility that they are older.

An Unexpected Find Prompts Waiting for Additional Resources

Some experts said the microspherules were “weird looking.”Meyer serendipitously discovered the silica-rich “glass pearls” when he was a University of South Florida undergraduate student participating in a summer fieldwork project led by Roger Portell, director of the invertebrate paleontology collection at the Florida Museum of Natural History and a coauthor on the new study.

Meyer and other students searched for benthic foraminifera enclosed in fossilized clams in a Sarasota, Fla., quarry. There, a 4.5-meter-tall section of the Plio-Pleistocene Upper Tamiami Formation was exposed. (The quarry is now sealed up and part of a development, according to Meyer.) Meyer and the other students collected eight sediment samples and used five different sizes of meshes to sieve the samples.

The microspherules were found only with a 98-micrometer sieve, the study notes. A paintbrush coated with tragacanth gum was used to remove the tiny structures from the samples and mount them on micropaleontology slides.

Experts think many more microtektites have yet to be found in Florida. Credit: Mike Meyer

Right after happening upon the glass spheres, Meyer emailed researchers to ask if any of them knew what he might have. Some experts told him the microspherules were “weird looking.” They suggested different techniques he might use to further study them, but those required expensive equipment and detailed analyses outside of the scope of the resources available to Meyer as a college student.

Meyer postponed his quest to identify the pearly unknowns.

A Reignited Search

After Meyer earned his doctorate and began working at Harrisburg University, he resumed looking for answers.

Coal ash and fly ash contamination were effectively ruled out as the source of the microspherules. Coal ash particles are usually between 0.1 and 20 micrometers in diameter and tend to have irregular shapes, the researchers wrote. “Fly ash is also more heterogeneous in composition,” with higher concentrations of aluminum and iron than those of the tiny spheres.

Other types of contamination were also noted as unlikely sources, given that the specimens are found only in certain layers of raw sediment and within articulated shells.Researchers suggest the microspherules are microtektite debris from a previously unknown impact event.

The microspherules’ spectroscopy data were compared to those of volcanic rocks, microtektites, and micrometeorites. “A volcanic origin is unlikely,” not only because there aren’t any known volcanoes nearby but because the microspherules have high sodium concentrations.

The microspherules’ high sodium concentration also indicates the objects are not micrometeorites. The sodium suggests “significant evaporation has not occurred, ruling out micrometeorites, since they experience substantial heating and evaporation during atmospheric entry,” according to the study.

Meyer and his coauthors ultimately suggest the microspherules are microtektites from a previously unknown impact event. As for the high sodium concentrations? They could be explained by a meteor’s impact into carbonate-rich sediments, a smaller impact, or one that occurred close to where the objects were deposited.

The study is “fascinating,” but more work is needed to constrain the ages of the microspherules, study the specific cause of their high sodium concentration, and investigate the impact that may have created them, said Scott Harris, a planetary geologist at Fernbank Science Center in Atlanta who wasn’t involved with the study.

Additional specimens are needed for these analyses, and Meyer has asked Florida fossil clubs to share similar microspherules as they are found.

—Rachel Crowell (@writesRCrowell), Freelance Science Journalist

The global space industry is on the verge of a great increase in the number of rockets launched into Earth orbit. The global launch rate has already more than doubled in the past decade. Transformational innovations such as rocket reusability, thousand-satellite constellations, space tourism, global surveillance, tracking of the Internet of Things, proliferated low-Earth-orbit constellations, and other emerging technologies are expected to further supercharge launch demand in coming decades. The space industry, already an indispensable part of the global economy, is preparing for a surge in growth of a kind not seen since the birth of the space age.

As the number of launches increases, rocket engine emissions increase in proportion. Rocket engine exhaust contains gases and particles that can affect Earth’s climate and ozone layer. These emissions historically have been assumed to be not much of a threat to the global environment because the space industry was deemed small and unchanging. Whether that assumption holds true for today’s rapidly growing space is an important question that needs scientific attention.

The Nature of Rocket Emissions

The various rocket engine propellants produce different emissions. The most common gaseous emissions are water vapor and carbon dioxide from liquid and solid fuels, as well as hydrochloric acid from only solid fuels. The global quantities of these gas emissions from rockets, even at increased launch rates, do not significantly affect the global climate or ozone layer, and they are dwarfed by atmospheric inputs from other sources [Larson et al., 2017].

Because of the unique nature of their combustion chemistry, rocket engines emit large amounts of black carbon when compared to, for example, a modern jet engine.As an important aside, water vapor emissions from individual launches can notably impact the mesosphere and ionosphere. Increased polar mesospheric cloud blooms, attributed to specific launches, have been frequently observed [Stevens et al., 2012]. Transient dropouts in electron content have also been observed in expanding ionospheric plumes, mainly from their impact on space-based navigation signals. Although not presently a global concern, at some increased launch rate, upper atmosphere launch plumes will become ubiquitous and so affect global mesospheric and ionospheric processes and properties.

Particulate emissions from rockets, on the other hand, could have important impacts on climate and ozone [Ross and Sheaffer, 2014; Voigt et al., 2013]. Rocket engines emit various amounts of submicrometer-sized particles of soot (or black carbon, BC) and alumina (aluminum oxide) directly into the stratosphere. Because of the unique nature of their combustion chemistry, rocket engines emit large amounts of BC when compared to, for example, a modern jet engine. During flight through the stratosphere, BC can account for as much as several percent of the rocket emissions [Simmons, 2000]; the equivalent measure for a modern jet engine is smaller by a factor of 100. In 2018 BC-producing rockets (all but the hydrogen fuel type) emitted about 225 tons of BC particles into the stratosphere, comparable to the annual amount of BC emitted by global aviation [Stettler et al., 2013]. Meanwhile, solid-fueled rockets emitted about 1,400 tons of alumina particles into the stratosphere.

Because particles emitted by rockets are small, they reside for 3 to 4 years in the stratosphere, where they accumulate. The “black” BC particles absorb solar radiation and slightly reduce Earth’s albedo. The “white” alumina particles reflect solar radiation and so increase the albedo slightly. Paradoxically, however, both have the same consequence for the underlying atmosphere: a reduction in the intensity of solar flux entering the top of the troposphere. Solar flux reductions caused by stratospheric particles are well understood to cool the lower atmosphere [Caldeira et al., 2013]. Therefore, and perhaps unexpectedly, rocket launch emissions contribute to cooling of Earth’s lower atmosphere and surface.

Globally averaged, present-day rocket particle accumulations cool the troposphere by about 0.02 watt per square meter [Ross and Sheaffer, 2014], whereas carbon dioxide emissions from global aviation warm the troposphere by about 0.03 watt per square meter [Lee et al., 2009]. Although these two effects involve different physics, the comparison nevertheless provides a useful context for understanding the relative magnitude of the climate impact of rocket launches. The magnitude of present-day cooling from rocket particles is about the same as the magnitude of warming from aviation carbon dioxide. In other words, rocket launches cool Earth’s surface by about the same amount that aviation warms it.

It would be an overinterpretation to conclude that rocket cooling mitigates some greenhouse gas (GHG) warming. Research shows that Earth responds to stratospheric particle injections in complex ways, with some atmospheric regions becoming warmer and others cooler, on subglobal and subseasonal scales [Kravitz et al., 2012]. Similarly, Earth will respond to rocket particle injections in complex ways. Unraveling this complexity and accurately assessing the potential effects of the coming surge in rocket emissions require sophisticated computer modeling efforts. Such efforts have yet to be realized.

Past Is Not Prologue

If particles emitted by rocket engines can affect climate and ozone, why have they not been the focus of much research?

With 114 launches in 2018, the number of launches has been growing at an average rate of about 8% per year for the past decade. Rocket emissions have also been growing.The answer is, in part, related to the history of rocket launches. The annual rate of rocket launches increased rapidly after the start of the space age, peaking at 157 launches in 1967. But then it declined over the next 4 decades, decreasing to only 42 launches in 2005. So for most of the past half century, rocket emissions have been in decline and therefore were not of much interest to researchers working to understand the most significant aspects of climate change and ozone depletion.

But that historic trend reversed in 2005 and, despite the retirement of the Space Shuttle in 2011, launch numbers began rising again. With 114 launches in 2018, the number of launches has been growing at an average rate of about 8% per year for the past decade. Rocket emissions have also been growing, faster than global emissions from other sources with comparable impacts, such as aviation. And this growth is expected to accelerate.

Dozens of companies and government agencies around the world are planning to launch and maintain tens of thousands of satellites in vast low–Earth orbit constellations over the next decade [Cates et al., 2018]. Several of the constellations have already started deployment. Even if only half of these plans are successful, the U.S. launch rate alone will double to about 200 launches per year by 2025. Following the historical pattern, other spacefaring nations will develop and launch similar satellite systems, adding roughly an additional 200 annual launches, meaning a scenario with 400 orbital launches per year globally by 2030 is very plausible.

Four Hundred Launches per Year

The global impact of 400 rocket launches per year is unknown. The series of models required to investigate this scenario have not been run, and the required plume measurements have not been made. In fact, only one detailed model of rocket BC particle emissions has ever been run—by us and a third colleague [Ross et al., 2010]. This lone effort provided surprising, if as yet unverified, clues.

Astronaut Mike Hopkins photographed the plume of the 10 October 2013 missile launch as it expanded in the upper atmosphere. Studies of rocket plumes can provide important information on diffusion processes throughout Earth’s atmosphere. Credit: Mike Hopkins, NASA

The 2010 global climate model study considered rocket BC emissions of 600 tons per year, more than double the current BC emissions of about 225 tons. Run for 40 model years to ensure the model reached steady state, the stratospheric BC burden grew to 2,400 tons. Although the globally averaged surface temperature anomaly was small and not statistically significant, on smaller scales and over limited latitude bands, significant positive and negative temperature anomalies emerged. North polar surface temperatures increased by more than 1°C, and upward of 5% of polar sea ice coverage was lost. And beneath the main BC accumulation in the northern midlatitudes (around the latitude of the assumed launch site at 33°N), the surface cooled by 0.5°C.

The complexity and magnitude of the predicted changes, for a mere 600 tons of annual BC emission per year, were remarkable.  But we emphasize that this study provided only a preliminary assessment of Earth’s potential sensitivity to the unique character of rocket BC emissions. The model did not consider alumina emissions, which could conceivably have a larger impact than BC, reflecting sunlight back to space. And the results have not been confirmed with more sophisticated models.

In 2010, a scenario with 600 tons of rocket BC emission per year was considered speculative. Today, that scenario might be considered reasonable. At a rate of 400 launches per year, stratospheric BC emission could reach 800 tons per year, and alumina emission (assuming unchanging relative propellant use) could approach 5,000 tons per year.

A new source of stratospheric particles may soon add to these increasing rocket emissions. Geoengineering is a set of plans to mitigate GHG climate forcing. One type of plan envisions the continual release of carefully chosen particles into the stratosphere to reduce incoming solar radiation, just as rocket particles do today, though on a much larger scale. Scientists and policy makers struggle to envision a suitable and effective international governance framework to address such purposeful injection of particles into the stratosphere; the National Academy of Sciences convened a special study on the topic [MacMartin and Kravitz, 2019].

Space launches are not, by any means, linked to geoengineering, and the two are very different in terms of benefits, risks, costs, and ethics. Still, the significant scientific efforts underway to understand theoretical geoengineering particle releases, while actual rocket particle releases continue without much scientific attention, raise new questions. How could geoengineering be monitored and regulated in the presence of escalating rocket launch particle injections? Could studies of rocket plumes inform geoengineering efforts with needed information on the behavior of particles in the stratosphere? Current efforts to assess the background state of stratospheric particles should account for space activities including particle production during launches and reentry “burnup.”

A Way Forward

The anticipated surge in emissions directly into the stratosphere would push the climate impacts of rocket emissions to be comparable in magnitude to other sources of climate change that receive intense study.As the space industry heads toward a future with two or three launches every day, the anticipated surge in emissions directly into the stratosphere (assuming current propellant types) would push the climate impacts of rocket emissions to be comparable in magnitude to other sources of climate change that receive intense study by international groups of scientists, engineers, and scholars.

The obvious example is the continued scrutiny of the global impacts of emissions of supersonic transport fleets [e.g., Ingenito, 2018]. Such aircraft have not flown in 2 decades and are unlikely to reappear in the coming decade, despite multiple efforts to address efficiency, noise, and safety. Meanwhile, despite the coming surge in launches, similar questions are not being asked about rocket emissions.

A recent policy analysis [Ross and Vedda, 2018] showed that the most advantageous course of action for addressing launch emissions is to gather data before a tipping point is encountered. Tipping points produce unforeseeable changes in perception, arrive suddenly, and disrupt the status quo by emphasizing uncertainties. A policy that raises the appropriate scientific questions and provides resources to investigate them would place the launch industry on a path to avoid a potentially disruptive tipping point.

A suitable first step on this path would be to convene a rocket emissions advisory panel that would include representatives from the industrial, scientific, and governance communities. This panel would determine the scope of the concern, identify additional actors and stakeholders, define early metrics, and uncover key knowledge gaps. Importantly, the panel would help build a foundation for future cooperative studies of the relative importance of rocket emissions to other processes and help to ensure that future research programs are in proportion to the significance of the impacts being studied.

Perhaps prominent organizations that have funded initial geoengineering experiments would value an in-depth understanding of the relationship between rocket particles and geoengineering particles.Patronage for such a forward looking panel is not obvious. The launch industry does not have a formal relationship with the science community, as does aviation. Philanthropic and public interest organizations that support sustainable development might sponsor the first advisory panel. Industry, science, or government organizations could take a wider view of their responsibilities, beyond what is now required or codified, to include the atmospheric impacts of rocket emissions. Perhaps prominent organizations that have funded initial geoengineering experiments would value an in-depth understanding of the relationship between rocket particles and geoengineering particles, including stratospheric processes common to both.

AGU could play a precipitating role with a statement of science policy regarding the scientific implications of a rapidly growing space industry. A Chapman Conference could possibly serve as a means to assemble an initial rocket emissions advisory panel.

The sooner that reliable and verifiable information can be compiled and assessed, the sooner effective strategies can be defined to reduce risks and limit exposure of the space industry to entanglement with geoengineering experiments and regulations that are not well aligned with long-standing space launch practices and traditions. Adoption of a long view with regard to emissions has well served the ambitious growth goals of the aviation industry. Such a view would do the same for the space industry.

 Many people have emergency kits packed to flee or survive forces of nature like floods, hurricanes, or wildfire. But what do you throw in your bag when you expect to rush toward a natural hazard?

Geologist John Ewert has his go-kit packed with portable seismometers and gas-monitoring equipment, ready to mobilize when a volcano starts to rumble.

Ewert started his career at the U.S. Geological Survey’s (USGS) Cascades Volcano Observatory in Vancouver, Wash., in 1980, months after the explosive eruption of Mount St. Helens awakened the residents of the western United States to the presence of slumbering giants in their backyards. He has encountered a wide variety of volcanoes and volcanic personalities as a founding member of USGS’s Volcano Disaster Assistance Program (VDAP), an emergency response team of scientists prepared to deploy to awakening volcanoes around the world at the request of local science agencies or governments.

Volcanologists pushed for the development of a response team and tools to explain the dangers of volcanoes across cultural and language barriers.VDAP organized in 1986, when few of the world’s volcanoes were monitored and agencies had little seismic equipment on the shelf available for deployment in an emergency. Multiple tragedies inspired the creation of VDAP: Thousands died in the eruptions of El Chichón in Mexico in 1982 and Nevado del Ruiz in Colombia in 1985, and even in the United States, the seismic monitoring network was sparse. Volcanologists pushed for the development of a response team and tools to explain the dangers of volcanoes across cultural and language barriers.

Mount Pinatubo John Ewert installs a platform tiltmeter high on the east side of the lava dome that formed the peak of Mount Pinatubo. The site was obliterated by the formation of the caldera after the volcano’s major eruption in June 1991. Credit: Andy Lockhart

The program faced its first big challenge in 1991, at a volcano in the Philippines called Pinatubo. The VDAP team and the Philippine Institute of Volcanology and Seismology scrambled to get equipment on the mountain and analyze data.

But science was only half the job. The harder task, Ewert said, was gaining the trust of people living near the volcano. Ultimately, Ewert and his colleagues successfully persuaded the U.S. Air Force, Philippine government, and local indigenous communities to evacuate over 60,000 people—more than 20,000 from what proved to be the path of certain death when Pinatubo crescendoed on 15 June.

In this special Centennial episode of Third Pod from the Sun, Ewert talks about driving away from Pinatubo in the “scary dark” of ashfall, creeping along in a crowd of hundreds of thousands of evacuees, and using orange soda to clear the windshield when the wiper fluid dried up. He explains how every eruption occurs in a social and political context and how the deaths of 25,000 people below Nevado del Ruiz resulted from a communication failure.

As volcano monitoring has grown, VDAP scientists are increasingly called on more for consultation than emergency deployment to hazard zones. But communicating the risks and probabilities of volcanic hazards remains a perennial puzzle.

—Liza Lester (@lizalester), Contributing Writer

Earth’s core is a hot, dense reservoir driving geological processes from the heart of our planet. The core is often described in two parts: a solid iron-nickel inner core surrounded by a liquid outer core of similar alloys. Convective currents in the outer core generate Earth’s magnetic field, preventing the planet’s atmosphere from being stripped away by the solar wind and making life on Earth possible.

But sitting beneath our feet under 2,900 kilometers of rock, Earth’s core is more inaccessible than the surface of Mars. No probe can directly sample the core-mantle boundary, and the planet’s inner structure has been deduced from seismology, not observation.

There may, however, be a work-around.

Isotope Ratios in Volcanic Island Rocks

Earth’s core may be interacting and even exchanging material with the lower mantle.In a paper in Geochemical Perspectives Letters, Hanika Rizo, an assistant professor of isotope chemistry at Carleton University in Ottawa, Ont., and her colleagues describe evidence that Earth’s core may be interacting and even exchanging material with the lower mantle.

The scientists studied magma-derived rock samples from volcanic islands above oceanic hot spots. These islands, such as Réunion in the Indian Ocean, sit atop rising columns of hot material that many geologists think originate as deep as the core-mantle boundary. If there were materials from the core getting into the mantle, Rizo said, these mantle plumes would be their paths to the surface, and she and her team were able to use newly precise measurements of a chemical isotope tracer to detect this.

The chemical tracer is an isotope of tungsten (W), its composition a remnant of Earth’s formation. When Earth was still molten, it separated into an iron core at the center and a silicate mantle above. Siderophiles, metal-loving elements including tungsten, primarily accumulated in the core, leaving sparse concentrations in the silicate-dominated mantle.

“The hypothesis was that when the Earth’s core separated, the Earth’s core acquired a very specific and very different tungsten isotopic composition from the rocky part [of the planet],” Rizo said.

So when Rizo and her colleagues measured the ratio of two tungsten isotopes, 182W and 184W, they expected ancient mantle rocks to have a 182W/184W ratio about 200 parts per million higher than that of Earth’s core.

And that’s just what they found when they measured the 182W/184W ratio of old rocks, such as the 3.5-billion-year-old Mount Ada Basalt in Western Australia. Setting an arbitrary terrestrial standard at zero, the researchers found that those rock samples yield 182W/184W ratios around 13−15, whereas Earth’s core would plot at −200.

But in relatively younger samples from mantle plumes, Rizo and her team measured negative tungsten isotopic ratios, with Réunion Island samples registering as low as −20.2, those from the Kerguelen Islands in the Southern Ocean hitting −16.5, and samples from Hawaii reaching −7.2.

“What we’re saying in the paper is that less than 1% of core contribution into the source of mantle plumes is going to be able to shift the isotopic composition towards these negative values,” Rizo said.

But critically, those negative values are tungsten isotope ratios, not tungsten concentrations—the core still contains much more tungsten than the mantle, according to Richard Carlson, director of terrestrial magnetism at the Carnegie Institution for Science. The same amount of tungsten may migrate from core to mantle and mantle to core over time, but the 182W/184W ratio in the mantle would drop in value, whereas the ratio in the core would rise ever so slightly.

“This is how you can explain a change in W isotopic composition of the mantle by exchange with the core, without also seeing the mantle W concentration go up,” Carlson said. .

This schematic shows possible processes for core-mantle chemical interactions. HSE = highly siderophile element; LLSVP = large low-shear-velocity province; ULVZ = ultra-low velocity zone. Credit: Rizo et al., 2019

. And there are good reasons, in addition to the new evidence of Rizo and her colleagues, to believe that core-mantle interaction is limited to this type of isotopic exchange, according to Carlson. In fact, for a long time, many geoscientists were skeptical there could be any core-mantle interaction at all. “You’ve got a core that’s, you know, 3 times denser than the silicate overlying it,” he said. “With that magnitude of a density difference, the expectation for the core and the mantle to mix back together over time is very low.”

Explanations for Shifting Isotope Ratio

There are competing theories to explain the shifting tungsten isotope ratio. One hypothesis is meteoritic bombardment after Earth formed, Rizo said. Chondritic meteorites have a tungsten isotope profile similar to that of Earth’s core, so a significant meteor bombardment that was later mixed into the mantle could bring those positive tungsten isotope ratios back toward zero.

“It was basically changing the isotopic composition from above, whereas Hanika’s paper is changing it from below by mixing with the core,” Carlson said.

But if there were such a bombardment, known as the “late veneer,” Carlson said, it would have ended very early in Earth’s history and doesn’t explain the isotopic composition of younger rocks from mantle plumes.

It’s not yet clear whether the core has always been interacting with the mantle or whether the interaction began later.It’s also not yet clear whether the core has always been interacting with the mantle or whether that interaction began later. Earth’s oldest rocks show consistent, high 182W/184W ratios from 4.3 billion to 2.7 billion years ago, Rizo said, whereas rocks that are 2.5 billion years old and younger show isotope ratios that trend more negative. It could be that the core has always been leaking material into the lower mantle, but it took later convection in the form of deep slab subduction to mix that material up.

But an alternative explanation posits that Earth’s core started out all liquid, with the inner core crystallizing later. This crystallization could have forced any oxygen there into the still-liquid outer core, Rizo said, which would then force the exsolution of tungsten out of the core.

“The variability that we are measuring in the tungsten isotopic composition of the rocks,” Rizo said, “if it is related to the crystallization of the inner core, we might be able to find evidence of when the inner core started crystallizing, when the dynamo started, and when our magnetic field started.”

Future research may help answer some of these remaining questions, and that field is just beginning, according to Graham Pearson, a professor of Earth and atmospheric sciences at the University of Alberta.

“In the early 2000s, late 1990s, the analytical precision just wasn’t good enough to be able to make the measurements at the required precision to show much of an effect,” he said. “That’s the beauty of what’s been happening more recently with a number of groups, including Hanika Rizo and colleagues, really improving the measurement precision capabilities.”

The results, Pearson said, are a solid endorsement of “blue sky science.”

“I think the field is now open for a lot more measurements on both young and old rocks to firm this picture up,” Pearson said.

—Jon Kelvey (@jonkelvey), Freelance Writer

In the traditional model of the earthquake cycle, a seismic event occurs when an active fault abruptly releases strain that has built up over time. About 20 years ago, however, seismologists began finding that some faults, or sections of faults, can experience slow earthquakes—a gradual type of aseismic slip, or “creep,” that can last for months. Because both types of events release pent-up energy, determining the proportion of seismic versus aseismic slip along active faults is crucial for estimating their potential hazard.

Although conventional interpretations predict that aseismic slip should occur at a roughly constant rate, geodetic observations have shown that at some locations fault creep is anything but steady. Measurements along the southern San Andreas Fault in California, one of the most studied examples of a creeping fault, have shown that this section often experiences bouts of accelerated creep and that these events can be spontaneous or triggered by seismic events. But the underlying conditions and mechanisms that cause slow slip are still poorly understood.

Now Tymofyeyeva et al. report detailed observations of a slow-slip event that occurred along the southern San Andreas Fault following the magnitude 8.3 earthquake that hit offshore Chiapas, Mexico, in September 2017. The team combined the results of field mapping with creepmeter and Sentinel-1 interferometric synthetic aperture radar observations to create a high-resolution map of surface displacements near the Salton Sea. The researchers then entered the results into numerical models to constrain the crustal properties that could generate the observed behavior.

The results indicated that surface slip along the 40-kilometer-long section between Bombay Beach and the Mecca Hills accelerated within minutes of the Chiapas earthquake and continued for more than a year. The event resulted in total surface offsets that averaged 5-10 millimeters, comparable to the slow slip triggered by the 2010 magnitude 7.2 El Mayor-Cucapah (Baja) earthquake, even though the stress changes along the southern San Andreas due to the Chiapas earthquake were several orders of magnitude lower.

The findings offer compelling evidence that the Chiapas earthquake triggered the 2017 slow-slip event along the southern San Andreas Fault, according to the researchers, and show that although shallow creep near the Salton Sea is roughly constant on decadal timescales, it can vary significantly over shorter periods of time. The authors conclude that the response of the southern San Andreas, and potentially other major faults, to different seismic events is complex and likely reflects crustal conditions as well as local creep history. (Journal of Geophysical Research: Solid Earth, https://doi.org/10.1029/2018JB016765, 2019)

—Terri Cook, Freelance Writer

The ion sensor on NASA’s Juno spacecraft has made the first in situ observations in the upper portion of the Jupiter ionosphere. Valek et al. [2019] reveal, rather surprisingly, bands of cold ionospheric protons in both the Northern and Southern Hemispheres, in a region just equatorward of the auroral oval on Jupiter, with energies below an electron volt.

Even more surprisingly, these cold protons are seen to coincide with populations of hot oxygen and sulfur ions with energies of one to ten thousand electron volts, precipitating from Jupiter’s inner magnetosphere. These hot, heavy ions are believed to heat the upper ionosphere, thereby raising the height of the cold protons and making them observable on Juno.

These unexpected observations shed important lights on how the dynamics of Jupiter’s ionosphere and magnetosphere are coupled together.

Citation: Valek, P. W., Allegrini, F., Bagenal, F., Bolton, S. J., Connerney, J. E. P., Ebert, R. W., et al. [2019]. Jovian high‐latitude ionospheric ions: Juno in situ observations. Geophysical Research Letters, 46, 8663– 8670. https://doi.org/10.1029/2019GL084146

—Andrew Yau, Editor, Geophysical Research Letters

Rep. Francis Rooney (R-Fla.) doesn’t understand why more Republicans aren’t on board about accepting the reality of climate change and doing something about it.

Most of the residents in Rooney’s heavily Republican congressional district believe that climate change is real, are scared of sea level rise, and want the government to take action, he said at a 19 September forum at the World Resources Institute in Washington, D.C.

Republicans “are self-sorting to a diminishing voting bloc and are failing to reach the growing voting blocs because of our intransigent adherence to rigid ideologies.”Republicans, Rooney said, “are self-sorting to a diminishing voting bloc and are failing to reach the growing voting blocs because of our intransigent adherence to rigid ideologies” on some issues, including climate change.

However, Rooney and Rep. Paul Tonko (D-N.Y.), who also spoke at the forum, said they hope there can be bipartisan progress to address climate change. In particular, both men spoke in support of carbon pricing, proposed legislation that would put a price on commercial greenhouse gas emissions.

Tonko, who chairs the House Committee on Energy and Commerce’s Subcommittee on the Environment and Climate Change, has said that a long-term goal is to work on a carbon pricing solution. “For far too long, we have allowed carbon to be a pollutant, to attack our atmosphere, to destroy our public health,” he said at the forum. “But we haven’t been formal or definitive about assigning a price to that carbon. And I think as we go forward, it’s important to work on this.”

Rooney, a sponsor or cosponsor of three carbon pricing bills, spoke in support of moderates addressing climate change. “The left beats up the moderates for not being left enough, and the right beats up the moderates for saying anything about carbon or climate at all,” he said. “We’ve got to somehow break through that and maybe see [that] the carbon tax is the best alternative for a market solution, and maybe convince the more extreme environmentalists on the left that this is a down payment as we move down the road toward maybe some things that you are interested in.”

Ways to Move Forward?

Rooney and Tonko said they hope there are other areas in which there can be progress.

“I just want to keep coming back to focus on specific things that we can do,” said Rooney. For him, these include focusing on carbon sequestration technologies, dealing with sea level rise and resiliency, and looking at improving infrastructure.

Tonko, who has laid out a framework for national climate action, said that some areas where he hopes for more bipartisan and bicameral support include increasing funding for research and development and improving infrastructure, energy efficiency, and weatherization. Another part of his framework is setting scientific targets for greenhouse gas neutrality by 2050.

Rooney said that he shares that 2050 goal “if it’s possible. I don’t know the practicalities of it. But I think that if you extend the Paris [climate accord] goals out and beat the Paris goals, you can get pretty far down the road on it.”

A Call to Embrace Science

“I won’t live with the cynicism. I’ll live with the optimism. Let’s get it done. Our planet deserves our attention. The next generation deserves our respect.”Tonko also spoke in support of respecting science in framing the climate debate, and he praised climate activist Greta Thunberg and her message delivered to Congress earlier this week.

“I say to Greta Thunberg, ‘hooray for you.’ There are two things I got from [her] message most prominently: ‘Science, science, science,’” he said. “And, ‘you’re not moving fast enough.’”

“Hooray for Greta for bringing her forces, her followers, to the equation of advocacy, because that is what will drive this,” Tonko added. “I won’t live with the cynicism. I’ll live with the optimism. Let’s get it done. Our planet deserves our attention. The next generation deserves our respect.”

—Randy Showstack (@RandyShowstack), Staff Writer

This story is part of Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story.

Students from the Washington, D.C., area lined up hours before doors opened at the MSNBC Climate Forum on Thursday, 19 September, at Georgetown University. Event staff said that two students actually arrived the night before, sleeping in the hallway of Healy Hall to guarantee their first place in line.

The 2-day televised climate forum gave 11 Democratic candidates and one Republican the floor for 1 hour each to discuss their stance on climate change. The forum may be fertile ground for presidential hopefuls: One in 10 eligible voters will be between the ages of 18 and 23 in 2020, and just 30% of the generation approves of President Donald Trump’s job performance.

The Climate Forum was cohosted by MSNBC and Georgetown University’s Institute of Politics and Public Service and sponsored by Our Daily Planet and New York magazine. MSNBC journalists Chris Hayes and Ali Velshi moderated the conversations, and questions included those from the student-only audience.

“Whoever is elected president in 2020 will decide whether the U.S. leads the world in fighting the climate crisis or watches as it happens,” Mikail Husain, a junior at Georgetown University, told Eos. Husain attended four talks on Thursday. “I want to learn as much as possible about every candidate’s plan.”

Former Maryland representative John Delaney addresses a student’s question. Candidates fielded questions from students for 30 minutes each following their one-on-one conversation with MSNBC host Chris Hayes. Credit: Jenessa Duncombe

The first day of the climate forum included Vermont senator Bernie Sanders, as well as Colorado senator Michael Bennet, entrepreneur Andrew Yang, author Marianne Williamson, former Maryland representative John Delaney, Ohio representative Tim Ryan, and former housing and urban development secretary Julián Castro. The event comes weeks after CNN’s 7-hour climate town hall that scientists praised as substantive and unprecedented for cable news.

Eos spoke with students at Georgetown attending the event and heard many students list climate change as one of their top issues for the 2020 election. Generation Z, as well as Millennials, are more likely to attribute climate change to human causes, with 54% saying that human activities led to climate change, according to a Pew Research Center survey. In the same survey, 22% said they weren’t sure about a link between human activity and climate change, and the remainder said either that climate change is due to natural cycles (14%) or that the Earth isn’t warming (10%).

Angelene Leija, a Georgetown University freshman, said that young people must lead the way on climate change because older generations “don’t want to admit that they played a part in what’s happening right now.” She said that although the Obama administration was “doing a good job” addressing climate change, the Trump administration steered off course at a critical time.

“Right when we needed it the most, we’ve gone in the opposite direction,” Leija said.

Several students told Eos that they were troubled about the future. Georgetown freshman Soumil Dhayagute said that climate change “is our generation’s biggest worrying cause, especially for our kids.” Another student voiced concerns for her family who live in Seattle and their health from wildfire smoke, and another noted worries about environmental migrants displaced by rising seas.

Esmeralda Paez, a sophomore at Trinity Washington University, said she’s undecided about her top candidate but said it might be California senator Kamala Harris, who did not attend the forum. Four other Democratic candidates—former vice president Joe Biden, Massachusetts senator Elizabeth Warren, Minnesota senator Amy Klobuchar, and former Texas representative Beto O’Rourke—also did not attend the 2-day event.

Political cartoonist and sophomore Alexandra Bowman drew live cartoons during the event, including this one about former vice president Joe Biden and MSNBC host Chris Hayes. Credit: Alexandra Bowman

“I was disappointed that Elizabeth Warren and Joe Biden didn’t come,” Georgetown University junior Kent Adams told Eos. Wearing a Bernie Sanders shirt, Adams voiced his support for Sanders, whom he’d arrived to watch.

Alexandra Bowman, a sophomore in Georgetown College, said that she’s “particularly interested” in Biden because “he seems to have the most relevant experiences to the presidency.”

The forum struck a chord with students. Over 700 seats in Gaston Hall were full, and a line of students stood outside waiting to get in during the event. “Political debates and town halls are my Super Bowls,” Bowman said. “I couldn’t pass this up!”

A second day of the climate forum begins 20 September, with New Jersey senator Cory Booker addressing the audience at 10:00 a.m. eastern standard time. The public may watch the event live at MSNBC’s live stream.

—Jenessa Duncombe (@jrdscience), News Writing and Production Fellow

This story is part of Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story.

Arctic melt season watchers had a wild ride this year, with sea ice extent plummeting, and tracking with all previous record lows for time-of-year from March through mid-August, as 2019 appeared on course to challenge 2012 — the lowest minimum in the 1979-2019 forty-year satellite record.

Then, once again proving the Arctic’s unpredictability, 2019’s melt slowed dramatically in late August and early September, only to take off again in a race to the bottom. As recently as Monday, extent appeared to be heading toward a fourth place finish behind 2016 and 2007, but overnight 2019 surpassed both, placing second only to 2012. And final results still aren’t in.

“This year what we’re seeing is a good example of the natural variability of the system,” says Mark Serreze, director of the National Snow and Ice Data Center (NSIDC). In the spring, it looked like we were heading for a new record low, but then, in August, the loss rate suddenly slowed.

2019 now ranks among the lowest ice minimums in the 40-year satellite record. More importantly, during the four-decade time frame, the world has witnessed monumental declines in ice extent and volume in the Arctic. “In all months, sea ice extent is going down,” reports Serreze, with the biggest changes seen at the end of the summer melt season. Compared to when the satellite record began in 1979, sea ice extent is down about 40 percent in September. “It’s a big loss,” he says.

By the numbers, the 1979 extent minimum, according to NSIDC, came in at 6.895 million square kilometers (2.662 million square miles), whereas by 2012 the September ice locked in at just 3.340 million square kilometers (1.289 million square miles). This year, as of September 17, sea ice extent sank to 4.100 million square kilometers (1.583 million square miles), shifting its ranking overnight from fourth to second place, surpassing 2007 at 4.147 square kilometers (1,601 square miles) and 2016 at 4.145 square kilometers (1.600 square miles).

In recent years, we’re starting to see more significant losses in other seasons, too, says Julienne Stroeve, a senior research scientist with NSIDC. “The changes in summer have been dramatic, but it’s starting to manifest in other seasons as well, with later freeze-up and earlier melt. We’re lengthening the [progressively] ice-free season.”

And sea ice isn’t only covering far less extent, it’s also getting thinner causing the volume of Arctic ice to drop precipitously, making the sea ice far more vulnerable to warming Arctic waters and atmosphere. With less thick, multiyear ice hanging around much of the sea ice in the Arctic is forming and melting away every year.

In 1979, the daily minimum for sea ice volume was 17,065 cubic kilometers (4,094 cubic miles). While 2019 has likely not yet reached its lowest point, at the end of August, volume had fallen to just 4,170 cubic kilometers (1,000 cubic miles), putting it in close second place behind 2012, and already 75 percent lower than the 1979 minimum.

Such dramatic changes in the ice are being driven by warmer air and water temperatures which eat away at the ice from all sides. Summers are longer than they used to be, and winters are warmer. “You put that together and you have a pretty strong formula for getting rid of ice,” says Serreze.

Still, that doesn’t mean ice loss has followed a clear downward trajectory with every year lower than the one that came before. Rather, based on the natural variability of the climate and summer weather patterns, the trend of sea ice extent creates a kind of “sawtooth pattern,” where year-to-year extent and volume vary, but the long-term trend is ever downward, in what has been dramatically dubbed “the Arctic Death Spiral.”

The “Arctic death spiral” of ice loss occurs in a sawtooth pattern rather than a smooth downward trajectory. Credit: NSIDC/NASA

Thus far, 2012 has experienced the lowest September sea ice cover in the satellite record. “It sticks out like the proverbial sore thumb,” says Serreze. But low years are increasingly more frequent and recent, with the top ten all occurring after 2007. And if global temperatures continue to rise — as expected in a world where nearly no nations are currently expected to meet their Paris Climate Agreement goals — that melting trend is bound to spiral downward.

How Ice Loss Affects Us All

With so few long-term climate data sets, the importance of the sea ice record is hard to overstate. Sea ice is an extremely sensitive indicator of changes in the global climate, and it’s also very visual — unlike, say, changes in the global average air temperature. “You look at satellite data and you can very well see what’s happening,” says Serreze. And then there are those stunning pictures of beleaguered polar bears whose feeding habits are impacted by sea ice loss — with other polar species seriously affected too.

However, climate change is now becoming increasingly visual beyond the Arctic, with impacts ranging from devastating hurricanes to long-term droughts and raging wildfires. One metaphor says that the polar regions act as the Earth’s air conditioners, while also helping to set up many of the basic weather patterns that we have come to expect around the globe in the past. But as the Arctic grows out of sync, so goes the rest of the planet,

“A strongly warming Arctic could influence weather patterns in the mid-latitudes,” says Serreze. As the saying goes: what starts in the Arctic, doesn’t stay in the Arctic.

Researchers are increasingly certain that the strong temperature differentials between the Arctic and the temperate zone are one of the primary factors that create and propel the northern jet stream — a fast-moving river of air in the Northern Hemisphere that circles the Arctic. As sea ice vanishes and Arctic temperatures increase, the temperature variant between these regions is getting smaller. That means there’s less force driving the winds in the jet stream from west to east, and the weakened jet stream starts to swing wildly, deviating from its typical polar path into lower latitudes (even as far south as the Gulf of Mexico) which can also cause temperate weather patterns to stall in place — bringing punishing bouts of extreme weather.

This spring saw one of the waviest jet streams in recent history, and in turn, severe weather slammed into much of the mid-latitudes. Bomb cyclones, severe thunderstorms, heavy rain and catastrophic flooding in the Mississippi River basin were all possibly born out of this year’s deeply askew jet stream. One possible impact could be the stalling of major storms, such as Hurricane Harvey over Houston, Texas; that storm’s stuck-in-place rainfall totals topped 60 inches in some locales.

The unprecedented melting of sea ice has other serious ramifications. Less ice means the Arctic is now open for business. The world’s superpowers are paying increasingly more attention to northern economic opportunities, and the region is now considered to be of significant geopolitical importance. US President Donald Trump’s sudden interest in Greenland is just one example. That country made headlines this summer for another reason, seeing a huge amount of glacial melt into the North Atlantic. Scientists now estimate that ice loss in Greenland this year alone was enough to raise the average global sea level by more than a millimeter — glacial melt that is only expected to escalate, unless the world’s nations and corporations act aggressively to limit greenhouse gas emissions.

The Arctic has large deposits of natural gas, oil and rare earth minerals, as well as methane hydrates, that if mined, would likely be game over for reestablishing a stable global climate. Moreover, the loss of ice has opened up shipping routes, such as the Northern Sea Route over Russia, and the Northwest Passage in Canada. “Right now, both [routes] are open. It’s pretty much clean sailing,” says Serreze. “I’ve been studying the Arctic years, but now I’ve unavoidably been drawn into issues of climate change and geopolitics.”

Future of Forecasting

Despite the 40-year record, it’s still difficult for ice scientists to know how the melt season will shake out each year. Ice predictions are constrained by limited forecasting abilities for the natural variations in weather.

Scientists like Stroeve are working on ways to improve measurements of sea ice thickness, which helps to inform ice forecasts. Currently, researchers aren’t able to directly map sea ice thickness in summer (relying on modeling for their statistical analysis), and are limited by how much snow lies atop the ice in other months. “That’s something we don’t observe well from satellites. Our understanding is pretty rudimentary. We have to make assumptions based on snow depths,” she says.

The other big barrier in predicting sea ice outcomes is the accuracy of long-term weather forecasts. Right now, scientists can’t predict how natural variations in weather will impact the ice in the long run. Stroeve calls this the “spring predictability barrier,” which means that any ice forecast made before May isn’t very accurate. “Once you get to June, things get better.”

In a sense, long range forecasts are easier. Without governmental and corporate action to curb carbon emissions, the global trend in Arctic sea ice will almost certainly be downward — with impacts both seen and as yet unforeseen, for us all.

This story originally appeared in Mongabay. It is republished here as part of Eos’s partnership with Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story.

Around the world, cities are often a few degrees hotter than surrounding rural areas. A recent study verified that across the world, the intensity of this so-called urban heat island effect depends on a city’s population and how much rainfall it receives annually.

If a city sits in a lush and verdant region, “vegetation still helps, but you need many more trees to get the same effect.”One key factor, according to lead researcher Gabriele Manoli, is how much water is exchanged with the atmosphere by a city compared with the surrounding land. “Evapotranspiration…is the process of transferring water from the soil into the atmosphere, regulated by vegetation,” Manoli, an environmental engineer at University College London, told Eos. “This process has a cooling effect on the Earth’s surface.”

Adding green space to a city is a common strategy to mitigate urban heat. If a city has more greenery than the surrounding area, the urban heat island (UHI) intensity will be relatively mild, Manoli’s team found. But the study suggests that if a city sits in a lush and verdant region, “vegetation still helps, but you need many more trees to get the same effect,” he said.

Cool and Dry, Warm and Wet

Regionally, “it was known that there are two general trends: The intensity of urban heat islands increases with population and…with increasing precipitation in the region,” Manoli explained. “Population is a proxy for the size of a city, its form, activities, and infrastructures, while precipitation is a proxy for the local climate and vegetation characteristics.”

The researchers sought to verify and explain these trends on a global scale, so they gathered summertime surface temperature data from more than 30,000 cities around the world. They compared the average temperature inside a city to that of the surrounding undeveloped area—the UHI intensity—and compared that to a city’s population and amount of precipitation.

This map shows the intensity of the urban heat island effect in 30,000 cities around the world, calculated during the cities’ summertime. Hotter colors mark cities that are hotter than their surroundings, and cool colors mark cities that are colder than their surroundings. Credit: image by Gabriele Manoli, illustration by Beatrice Trinidad

The team found that the population trend held up on a global scale. “The bigger a city is, the warmer a city is,” Manoli said. UHI intensity also increased with precipitation but began leveling off when a city reached about 1,000 millimeters per year of precipitation.

Why? As a city grows, it replaces the vegetation in undeveloped areas with urban surfaces and some amount of greenery. This alteration changes how that parcel of land exchanges water with the air and how that air flows.

“If a city is surrounded by a desert,” he said, “then the city can be cooler than its surroundings because it can have green spaces that transpire water, it can exchange heat more efficiently than the barren land, and so on.” “Removing the natural vegetation and substituting it with urban surfaces…contributes to more intense urban heat islands.”

However, “tropical forests transpire and cool down the surface much more efficiently,” Manoli said. “In this case, removing the natural vegetation and substituting it with urban surfaces creates a large difference in evapotranspiration that contributes to more intense urban heat islands.” This research was published in Nature on 4 September.

Dan Li, an urban microclimatologist at Boston University in Massachusetts who was not involved with this study, called this “an important step towards bridging the gap between…urban scaling theory and the study of urban climate.”

According to Li, the study suggests that “if we get a good sense of how urban population changes, we can have a first-order estimate of how the urban heat island intensity might change in the future.” This claim will need to be verified by Earth system models that consider urban land expansion, he said.

Cooling Down Our Cities

These results emphasize the need for climate-sensitive urban planning and heat mitigation strategies, the team wrote. “Of course vegetation is beneficial for many reasons and can cool down a city,” Manoli said. “But the amount of green space that a city needs to significantly reduce the UHI effect, in terms of percentage of the total area, varies depending on the local climate.”

Strategies that increase green space and albedo will work best in drier climates like the United Kingdom but not for regions like Southeast Asia. Those areas, the team suggests, should also incorporate other cooling methods like shading and ventilation.

“To combat the urban heat island effect, you need a number of strategies,” Manoli said, “especially if you’re in hot, humid places like the topics.”

—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer

This story is part of Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story.

In winter 2018, the sea ice extent in the Bering Sea reached the lowest levels observed since 1850, when records began. By late April, warm, southerly winds left sea ice levels at just 10% of the 1981–2010 average for that time of year. In recent research, scientists studied how the unprecedentedly low ice cover affected ecosystems in the region.

As sea ice melts in the spring, it releases fresh water and nutrients into the ocean, seeding phytoplankton blooms that serve as the base of food webs. Researchers call the cascading connections between sea ice cover and the abundance of organisms in ecosystems the oscillating control hypothesis. This process has long been studied in the southeastern Bering Sea, where sea ice levels have contracted or expanded in accordance with multiyear temperature patterns, but not in the northern Bering Sea, which has never experienced a complete lack of winter sea ice.

Typically, springtime ice in the northern stretches of the sea keep ocean bottom temperatures low even at the height of summer, when a “cold pool” typically covers more than 70% of the continental shelf, making the northern reaches cold even when the south is warm. But the northern Bering Sea was not insulated during the winter of 2018, and by the following summer, the cold pool had virtually vanished. The unusual conditions gave Duffy-Anderson et al. a chance to find out whether the oscillating control hypothesis might serve as a model for trophic cascades in the northern ecosystem as well.

The researchers used satellite-based measurements of sea ice levels and collected data on ocean temperatures, salinity, oxygen levels, and fluorescence between late April and mid-October 2018. They also took biological samples or biomass estimates of phytoplankton, zooplankton, fish larvae, adult fish, and seabirds.

The team found that the springtime bloom of phytoplankton was delayed and that plankton levels remained low, which led to a low abundance of large zooplankton, though small zooplankton thrived. Samples of larval walleye pollock—one of the world’s largest fisheries—indicated that the larval stage of fish was largely unaffected. However, the authors reasoned that the changes in their food supply may still affect the larvae’s ability to survive long term. Indeed, estimates of pelagic foragers, including pollock, herring, and capelin, in later stages of development revealed that fish stocks were below average. Observations of seabird colonies indicated smaller populations, decreased reproductive success, and a greater risk of die-off events.

Ultimately, the authors conclude that the cascading ecosystem effects seen in the northern Bering Sea in 2018 were similar to those previously observed in the southeastern region of the sea. They caution that unique aspects of the northern Bering Sea ecosystem­, including a different light regime and a northward shift of adult fish populations, could mean its response won’t be exactly the same, however. Still, the model from the southeastern Bering Sea could provide researchers with important insights about what’s in store for the northern region in a warming world. And researchers may soon have the opportunity to find out if the similarities between the regions hold up over the long-term with Bering Sea ice levels nearly reaching record lows again in winter 2019. (Geophysical Research Letters, https://doi.org/10.1029/2019GL083396, 2019)

—Kate Wheeling, Freelance Writer

This story is part of Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story.

Satellite altimetry systems keep an eye on Earth’s environment from space, monitoring changes in the heights of ice sheets, glaciers, and forest canopies to record the effects of a changing climate. One such system, NASA’s Ice, Cloud, and land Elevation Satellite 2 (ICESat-2), was launched successfully on 15 September 2018 and is currently collecting critical measurements of the Earth system.

The cutting-edge lidar technology aboard ICESat-2 is optimized for the polar regions, where observations help researchers evaluate the current state of our ice sheets and sea ice. The satellite’s global coverage also delivers high-resolution measurements of tree heights, inland water reservoirs, cloud characteristics, and oceans, improving our knowledge of biomass estimates, water storage, atmospheric heat flux, and sea level. Since ICESat-2’s launch, data not only have met expectations but also provide a window into other potentially transformational science discoveries.

This record is our best opportunity to evaluate changes to the frozen regions of our planet and better predict their evolution under future climate changes.The original ICESat mission, launched in 2003, provided global altimetry measurements for more than 6 years and contributed to many important scientific studies. These studies quantified the mass loss in ice sheet margins, volume changes of active subglacial lakes in Antarctica, the declining thickness of sea ice in the Arctic Ocean, tropical vegetation heights, and atmospheric characteristics.

Ultimately, ICESat highlighted the need for sustained observations of the polar regions and substantiated the advantages of laser altimetry for other Earth science applications. ICESat-2 measurements will be used with data from ICESat and NASA’s Operation IceBridge airborne program to produce a record of height measurements over land and sea ice spanning more than 2 decades. This record is our best opportunity to evaluate changes to the frozen regions of our planet and better predict their evolution under future climate changes [Markus et al., 2017].

ATLAS Scans the Surface

The sole instrument aboard ICESat-2, the Advanced Topographic Laser Altimeter System (ATLAS), directs laser beams toward Earth’s surface and detects these beams as the surface reflects them back (Figure 1). ATLAS measures the distance between the illuminated surface and the satellite by precisely recording the travel times of the beams. As the satellite orbits Earth, it creates profiles of elevation measurements on the surface. These profiles are repeated every 91 days in the polar regions to enable evaluation of surface elevation changes in the cryosphere.

Fig. 1. An artist’s depiction of ICESat-2’s multibeam configuration. The time the laser light takes to travel from the satellite to Earth’s surface and back again indicates the height of the surface features below. Credit: NASA GSFC

ATLAS produces a visible green (532-nanometer) laser pulse at 10 kilohertz. This repetition rate allows a surface measurement every 70 centimeters along track. ATLAS laser pulses are split into six independent beams—each with a nominal surface footprint 17 meters in diameter—that are arranged into three pairs. Each pair consists of one high-energy beam and one low-energy beam, and each pair is separated from an adjacent pair by approximately 3.3 kilometers in the across-track direction. Within each pair, the two footprints are separated by 90 meters to facilitate measurement of local slope and to distinguish between regional surface slope and true elevation change over time using repeated measurements—an improvement over the single-beam configuration of ICESat [Neumann et al., 2019].

Over almost 12 months of operations, ICESat-2 has produced more than a trillion laser shots in support of science. Following its launch, the ICESat-2 project office and science team studied preliminary data to assess ATLAS performance and data quality. These analyses validated the capabilities of ICESat-2 for cryospheric studies and also indicated the mission’s broad potential in many diverse areas of study, some of which were unexpected. Here we highlight some of the mission’s preliminary observations and show how the measurements improve knowledge of our planet’s climate dynamics.

Ice on Land and Sea

Sea ice observations are critical for understanding and quantifying the response of the Northern and Southern Hemisphere ice covers to a warming climate. One of these observations is the sea ice freeboard—the height of the snow surface above the local sea surface (Figure 2).

Fig. 2. Arctic sea ice freeboard measurements from ICESat-2 show the ice growth over the 2018–2019 winter season. Credit: Ron Kwok, Jet Propulsion Laboratory, California Institute of Technology

ATLAS allows higher-resolution observations of the exposed sea surface amid the ice cover, which are crucial for freeboard calculations, by resolving narrow cracks, or leads, in the ice that could not be distinguished with previous technology. These freeboard measurements are used to derive sea ice thickness to support investigations of Earth’s energy budget as well as forecasts and projections of change.

Over glaciers and ice sheets, ICESat-2 data have exceeded expectations with their ability to resolve fine spatial features and make early assessments of seasonal height changes.Ice height measurements are also crucial for determining the current state of Earth’s terrestrial glaciers and ice sheets and to pinpoint where and why changes are taking place. Such measurements are important because the ice sheets store enough water to raise global sea level by more than 60 meters [Fretwell et al., 2013; Morlighem et al., 2017] and because glaciers provide drinking water for much of the world’s population.

Ice shelves are the floating parts of the ice sheet, and changes in their mass lead to loss of grounded ice. Monitoring the ice shelves and the status of rift structures tells us the impact of ocean and atmospheric forcing over time.

Over glaciers and ice sheets, ICESat-2 data have exceeded expectations with their ability to resolve fine spatial features and make early assessments of seasonal height changes that contribute to the 20-year time series. The incredible spatial resolution of ICESat-2 data is highlighted in Figure 3, which shows a transect over a rift on the Filchner-Ronne ice shelf in Antarctica. The data show details of the rift’s structure as well as the changes based on comparison with an ICESat track from 2008.

Fig. 3. Elevation measurements from the ICESat (2008) and ICESat-2 (2018) missions over Antarctica’s Filchner-Ronne ice shelf show how the structural characteristics of the ice shelf have changed over time. ICESat-2’s path as it crossed over a rift in the ice sheet (left). Elevation measurements give a cross-sectional view of the widening rift (right). Credit: Catherine Walker, NASA Goddard Space Flight Center/UMD/Woods Hole Oceanographic Institution

Analyses of preliminary data also show the level of precision possible with the new instrumentation. These analyses suggest that land ice heights determined from repeated ICESat-2 measurements fall within 13 centimeters of each other, and over kilometer-scale lengths the precision improves to within 2–3 centimeters.

Fig. 4. This image, constructed using 5 months’ worth of elevation data over Antarctica, highlights ICESat-2’s coverage. This coverage does not include 4° circles at the poles (gray dot at center of map). Credit: Benjamin Smith, University of Washington

ICESat-2 Antarctic data coverage from the first 5 months of the mission is such that even the northernmost parts of Antarctica have measurements separated by no more than 6 kilometers. Figure 4, which shows the aggregation of the ICESat-2 land ice measurements for October 2018 through February 2019, offers an example of the mission’s thorough data coverage.

Measuring the Forest Canopy

Quantifications of biomass rely on tree height measurements, which are calculated from height differences between the treetops and the ground surface. In some laser measurements, however, the laser energy is absorbed or scattered within the treetops and doesn’t reach the ground surface. Lidar, as employed in ICESat-2, is unique in remote sensing for its ability to provide measurements throughout the full vertical structure of forests. This capability supports studies of terrestrial ecology and vegetation by providing direct assessments of tree heights.

Fortunately, preliminary data have shown ICESat-2’s ability to retrieve information on both canopy top and terrain heights in many types of ecosystems. Figure 5 depicts an ICESat-2 data transect, showing each photon detected. The color scheme indicates the designation of signal and background noise (gray points). This higher-level data product for land vegetation uses additional algorithms to distinguish photons reflected from the ground from photons reflected from the tree canopy (all of the tree branches and leaves) and, specifically, from the canopy top (the maximum tree heights).

Fig. 5. ICESat-2 subtropic measurements over Brazil show elevation changes along the satellite’s path. Background photons (gray dots) are distinguished from photons reflected from the tree canopy (blue), the canopy top (green), and the ground surface (red). Credit: Amy Neuenschwander, Applied Research Laboratories, University of Texas at Austin Shallow-Water Bathymetry

The capability to measure bathymetry in shallow-water environments is potentially transformational: It allows scientists to study coastal regions and coral reef zones and how they are changing. In some conditions, the green light of the ATLAS laser penetrates water for measurement of underwater topography, as shown in Figure 6. This capability will also allow scientists to derive volumes of inland water bodies to help quantify Earth’s global freshwater stores.

Fig. 6. ICESat-2 can make bathymetry measurements in shallow water. This data transect over Saint Thomas, U.S. Virgin Islands, shows the measurements of land surfaces both above and below the water surface. The submerged topography eventually disappears as the depth under the water increases. Credit: Lori Magruder, Applied Research Laboratories, University of Texas at Austin Fig. 7. These January 2019 ICESat-2 transects over Antarctica’s Amery ice shelf melt ponds show how ICESat-2 can measure elevations for both the water surface and the ice surface below. The difference between the two elevations gives water depth. Credit: Helen Amanda Fricker, Scripps Institution of Oceanography

Over ice sheets and sea ice, ICESat-2 photons penetrate surface water in melt ponds that form in some regions during summer; measurements of the depth of melt ponds (water surface minus ice surface; Figure 7) will provide insight into the dynamics of the annual melt season.

Looking Ahead

Since the public release of ICESat-2 data began on 28 May through the National Snow and Ice Data Center, the science community has started exploring this wealth of global height data. We look forward to the numerous collaborations and new insights that will emerge from the availability of these data.

Not only will the precision and resolution of the ATLAS data help create a 20-year record of change in the polar regions, vitally contributing to our understanding and accounting of the effects of climate change, but they will also likely revolutionize our ability to observe change across much of the planet.

Acknowledgments

This update is due to the successful design and development of ICESat-2. The authors recognize all of the scientists and engineers at NASA and present and past members of the ICESat-2 science teams, as well as the NASA Headquarters managers, Thomas Wagner, Charles Webb, and Colene Haffke.

I immigrated to New Zealand in 2001 to work at Niwa. That September, I made my first trip down the Selwyn River, from the headwaters near the Rakaia gorge across the Canterbury Plains to Te Waihora/Lake Ellesmere. The river was in flood, carrying mud, willow branches, irrigation hose and uprooted fenceposts to the lake. In a fever of scientific zeal, I launched an investigation of the effects of floods on river ecosystems.

I returned to the Selwyn in November to ask local farmers for access to sampling sites across their paddocks. The first site I visited had no water – just a gravel-lined channel on the flat plains. The second and third and all remaining sites were also dry. That was an unnerving day.

It took several more field trips to grasp that the Selwyn is a naturally intermittent river. When river flow from the headwaters reaches the plains, it seeps down through the coarse gravel bed to the water table 10-20 metres below the surface. Rapid seepage leads to the loss of all surface flow within 5km. A talk with any of the farmers I visited in November would have informed me that most of the Selwyn is dry for most of the year. But I was new to New Zealand and didn’t know to ask.

Drying has pervasive effects on every ecological variable we thought to measure, from biodiversity to water quality.Since the dry riverbed characterises the Selwyn River more often than floodwater, we shifted the focus of our research from the effects of flooding to the effects of drying. The study lasted six years, kept a team of scientists and university students gainfully employed, and greatly expanded our understanding of intermittent rivers.

There were two big revelations for me. First, drying has pervasive effects on every ecological variable we thought to measure, from biodiversity to water quality. Second, naturally intermittent rivers are giving us a preview of the effects of climate change.

In areas of New Zealand that are undergoing drying trends, many rivers that are currently perennial will become intermittent. Summer low flows are already trending downward in some perennial rivers and will eventually reach zero. Alteration of flows in these rivers by storing and returning irrigation water may modify these trends, but they are inevitably downward in drying areas.

What physical and biological changes can we expect when perennial rivers begin drying?

It’s unlikely that a perennial river will simultaneously dry over its entire length. Instead, the point in the river where flow is currently lowest will dry first, and the dry reach will gradually expand upstream and downstream as runoff declines and the groundwater table drops. These expanding dry reaches appear annually in naturally intermittent rivers like the Selwyn, Orari, Pareora and Waipara. Dry reaches are impassable barriers to migratory fish such as eels and bullies; mature female eels can’t reach the coast for their ocean spawning migrations and the returning juvenile eels can’t move from the coast to inland tributaries. Larval bullies can’t drift downstream to estuaries or return as adults.

Complete loss of flow may take decades to occur. In the meantime, what will happen to the life in these rivers?Life in an intermittent river is not benign. At the start of the drying cycle, fish and invertebrates are trapped in isolated pools, which attracts predatory birds. The pools rapidly heat up and then dry, along with their inhabitants. Invertebrates that are capable of burrowing or breathing atmospheric oxygen can survive in dry river gravels temporarily, but are eventually killed by desiccation and heat stress. Aquatic species can only persist in intermittent rivers if they recolonise when flow resumes, and slow colonisation means that intermittent rivers inevitably have fewer species than perennial rivers.

Despite the negative effects of drying, there are also some possible benefits. One is that native fish and invertebrates may find refuge from predation by non-native trout when they are separated from the trout by dry reaches. Species that are highly resistant to drying, such as mudfish, may find refuge from predators in gravels beneath dry reaches. Increased intermittence due to climate change may be a boon for these species.

In some rivers affected by climate drying, complete loss of flow may take decades to occur. In the meantime, what will happen to the life in these rivers?

Seasonal low-flow levels will decrease, with a corresponding loss of habitat. Maximum water temperatures will increase, which has the dual effect of increasing metabolic stress and reducing dissolved oxygen levels. Even now, we see fish killed by hypoxia in isolated pools in the Selwyn River. As with flow intermittence, reductions in aquatic habitat and increased water temperatures are likely to benefit some species. Predators take advantage of habitat shrinkage that concentrates their prey. And non-native species that tolerate high water temperatures and low oxygen, including koi carp and mosquitofish, will persist where sensitive native species are lost.

—Scott Larned, chief scientist freshwater for Niwa

This story originally appeared in stuff. It is republished here as part of Eos’s partnership with Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story.

Gareth Phoenix, a Professor at the University of Sheffield, studies Arctic ecosystems. In particular, the impacts of climate change on the ecosystem structure and function. The Arctic is vast and the changes occurring here — retreating glaciers, melting permafrost and shrinking ice caps — have the potential to dramatically impact the rest of the world.

Despite this, from a scientific point of view, much of the Arctic is unexplored and unknown. One thing we know for certain is that for approximately 35 years it has seen increasing growth of vegetation — a process known as ‘Arctic greening’. However, now it looks as though some of it might actually be turning brown.

When satellites in space detect plants on Earth they measure the ‘greenness index’, in other words, how green the ground cover of plants is. How lush the foliage on the ground appears from space can represent a number of aspects down on earth, from plant growth to leaf area. But if areas of the Arctic are browning, it may indicate something else as well: plant death.

The plant death can be a result of extreme weather events, which are becoming more frequent in the Arctic as the climate warms. A sudden period of warmth in the middle of winter tricks the plants into thinking it’s spring, so they burst bud early and lose their cold hardiness, leaving them unprepared for a return to normal cold winter temperatures. The plant die-back that follows the events of this ‘extreme winter warming’ also appear to be significantly reducing the ability of Arctic ecosystems to help combat climate change.

“We know that an increase in extreme weather events is a challenge we now face around the world as part of ongoing climate change. The fact that extreme events in the Arctic are killing tundra plants is a big concern because those damaged ecosystems are less able to take up CO2 to help combat climate change, and less able to provide habitat and food for the animals that rely on healthy tundra ecosystems for survival.”

The more the effects of climate change are felt by the Arctic the more they are felt by the rest of the world. What happens here has consequences beyond its icy boundaries. Therefore reducing greenhouse gas emissions, a primary contributor to climate change, is fundamental to reducing its impacts. Without making changes soon we might find the Arctic contributes to rising CO2 levels, rather than helping to combat it.

This story was originally published by the University of Sheffield. It is republished here as part of Eos’s partnership with Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story.

Youth from around the world descended on Washington, D.C., this week demanding action on climate change and demanding that Congress and others heed what scientists say about the threat it poses.

“I want you to listen to the scientists, and I want you to unite behind the science,” Swedish climate activist Greta Thunberg, 16, implored Congress while testifying at an 18 September House hearing jointly conducted by the Committee on Foreign Affairs and the House Select Committee on the Climate Crisis. The hearing was held just days before the upcoming United Nations Youth Climate Summit on 21 September.

“I don’t see a reason to not listen to the science,” said the soft-spoken teenager, who founded Fridays For Future to protest inaction about climate change. “[These are] not political views or my opinions. This is science.”

“We are already seeing the unacceptable consequences of [climate change] today, and it will only get worse the longer we delay action, unless we act now.”As part of her testimony, Thunberg submitted the Intergovernmental Panel on Climate Change’s Special Report on Global Warming of 1.5°C, which focuses on the impacts of global warming of 1.5°C above preindustrial levels.

“We are already seeing the unacceptable consequences of [climate change] today, and it will only get worse the longer we delay action, unless we act now,” she said.

Thunberg said that the way to get more youth involved in the issue is “to just tell them the truth.”

“When I found how [climate change] actually was, that made me furious so that I wanted to do something about it,” she remarked. “As it is now, people in general don’t seem to be very aware of the actual science and how severe this actual crisis is.”

She added, “We need to inform them and start treating this crisis like the existential emergency it is. Then I think people would understand and want to do something about it.”

Generation Green New Deal, Not Generation Z

Others testifying at the hearing included Jamie Margolin, 17, from Seattle, Wash., who founded Zero Hour to focus on climate change. “How do I even begin to convey to you what it feels like to know that within my lifetime, the destruction that we have already seen from the climate crisis will only get worse?” Margolin said. “By 2030, we will have known if we have created the political climate that will have allowed us to salvage life on Earth or if we acted too late. By then, we must be well down the path towards climate recovery, but this must start today.”

Margolin said that people refer to her generation, Generation Z, “as if we are the last generation. But we are not,” she said. “We are instead Generation GND, Generation Green New Deal,” referring to the aspirational congressional resolution that calls for dramatic action to confront climate change.

Benji Backer, 21, the president and founder of the American Conservation Coalition, testified that he, too, believes that climate change is real and that there is an urgency to act. However, he called for market-based solutions with limited government intervention.

“It’s time to claim our seat at the table,” he said, directing his comments to other conservatives. “There is a reasonable conservative response to climate change that we should embrace.”

“This generation is giving us a job to do. The job is addressing the climate crisis.”Without climate leadership on the left, “this issue would not be receiving the attention it deserves,” Backer said. He also laid out a challenge for liberals: “If you truly want to address climate change, work with conservatives who are ready to fight alongside you on implementing evidence-based policies.”

At the hearing, comments from members of Congress were mixed, though all praised the youth for their involvement and their testimony. “Climate change is real, and the best way to combat it is by reducing not only our nation’s carbon emission but that of the rest of the world,” said Rep. Adam Kinzinger (R-Ill.), ranking member of the Foreign Affairs Subcommittee on Europe, Eurasia, Energy, and the Environment. Kinzinger called for energy diversity and market-driven innovations to develop new technologies to help address climate change.

Rep. Kathy Castor (D-Fla.), chair of that committee, said that the youth climate movement “has grabbed the attention of the world” and that Congress needs to act on the urgency of the issue, including enacting into law the Climate Action Now Act, which the House has passed, to encourage the United States to remain a party to the Paris climate accord.

“People say this [young] generation gives us hope. But that’s not quite right, is it?” Castor said. “This generation is giving us a job to do. The job is addressing the climate crisis.”

A Global Focus

Also speaking out about climate change this week were youth from around the world who appeared at a 17 September briefing with Sen. Ed Markey (D-Mass.) and other members of Congress.

“No generation stands to lose more than the young people who have come to the United States Capitol today. Young people are leading the climate action movement around the world because for them, climate change is a matter of life and death,” said Markey. “The United States bears the historic responsibility of where we find ourselves today. Much of the CO2 [carbon dioxide] in the atmosphere is red, white, and blue.”

Artemisa Xakriabá, speaking at center, and other youth climate activists from around the world spoke at a briefing on Capitol Hill. Credit: Randy Showstack

“Right now, the Amazon, home to millions of my relatives, is burning,” said Artemisa Xakriabá, a member of the indigenous Xakriabá people of Brazil’s Cerrado tropical savanna ecoregion. “If it goes on like this, 20 years from now my house will become a desert and my people will be at risk of becoming history.”

“The governments of Brazil and the United States are not helping. They promote hate-based narratives and a development model that attacks nature and indigenous peoples. These governments are trying to put us in extinction. They are part of the problem,” said Xakriabá, who is a representative of indigenous and traditional communities that are part of the Global Alliance of Territorial Communities.

She said the countries should base their policies on scientific facts, reject products obtained at the expense of nature’s destruction, comply with international agreements, and guarantee the territorial rights of indigenous peoples and traditional communities.

Xakriabá and others also delivered a letter to members of Congress calling for the United States “to lead the community of nations into caring for our common home.”

At the briefing, senators, including Mazie Hirono (D-Hawaii), thanked the youth for their leadership on the climate issue. “When I hear things like, ‘I don’t believe in climate change,’ I want to say, ‘What do you think this is, a religion?’” she said. “To see [President Donald Trump] unilaterally withdraw from the Paris climate change [accord] means that our country has ceded, in my view, the leadership role that we can play in combating global warming and climate change. In this leadership vacuum, we see young people coming forward to provide the leadership that is lacking.”

—Randy Showstack (@RandyShowstack), Staff Writer

This story is part of Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story.

Developing Countries Are Already Tackling Climate Change. What’s Your Rich Nation’s Excuse? This opinion piece by Nigeria’s former finance minister puts into perspective the work going into the energy revolution: “Morocco recently built the world’s largest concentrated solar facility, serving 2 million people. South Africa’s robust renewable energy auctions led to solar and wind prices lower than prices from the national utility or from new coal plants. Kenya is the world’s 9th largest producer of geothermal power, which generates nearly half its electricity.”

—Heather Goss, Editor in Chief

 

Meet the Weather Observers on Climate Change’s Front Lines. What a delightful behind-the-scenes look! Weather observers check the temperature each day, and sometimes they witness a world record.

—Jenessa Duncombe, Staff Writer

 

Just How Environmentally Friendly Are All Those Scooters?

Credit: iStock.com/theverest

As I’m a scooter rider myself, this is food for thought. Taking an electric scooter is still better than driving a car the same distance, a recent study concluded. But the parent companies have all sorts of behind-the-scenes processes that give scooters a bigger carbon footprint than you (or I) would think.

—Kimberly Cartier, Staff Writer

 

Marooned: Researchers Will Freeze Their Ship into Arctic Ocean Ice for a Year.

The research vessel Polarstern, operated by the Alfred Wegener Institute, will intentionally moor itself near the North Pole. Credit: Alfred-Wegener-Institut/Martin Kuensting, CC-BY 4.0

Fully grasping the impacts of the warming climate on Arctic sea ice cover means getting up close and personal with the ice itself, so researchers can observe how it and its surroundings change from day to day. This is an excellent preview of an ambitious mission to do just that, with scientists (and journalists) serving rotations aboard a ship that’s to be locked in ice for a full year.

—Timothy Oleson, Science Editor

 

The Silenced: Meet the Climate Change Whistleblowers Muzzled by Trump. The Guardian spoke with six scientists who had their work altered or buried while at the U.S. Environmental Protection Agency and the Department of the Interior.

—Heather Goss, Editor in Chief

 

Climate Change Is Coming for Our Fish Dinners.

Credit: iStock.com/alle12

Human health and well-being could be at risk because of declines in the amount of omega-3 fatty acids available due to climate change and global warming.

—Faith Ishii, Production Manager

 

Material World. Technically, this is a book review of Bruno Latour’s Down to Earth, but really, it’s a persistently thoughtful way to critique and reframe how we think about climate change: “The environmental movement has politicized seemingly mundane objects, pushing us to analyze our meals, vacations, even children through an ecological lens, if only to defend our choices. But it has never managed to galvanize people and build power in the way that traditional political forces have. To the contrary, environmental politics seemed to leave most people cold. Making things ‘green’ seems to suck the life out of them” (emphasis mine).

—Caryl-Sue, Managing Editor

 

This story is part of Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story.