Climate

In 1721, a Norwegian missionary set sail for Greenland in the hopes of converting the Viking descendants living there to Protestantism. When he arrived, the only traces he found of the Nordic society were ruins of settlements that had been abandoned 300 years earlier.

There is no written record to explain why the Vikings left or died out. But a new simulation of Greenland’s coastline reveals that as the ice sheet covering most of the island started to expand around that time, sea levels rose drastically, researchers report December 15 at the American Geophysical Union’s fall meeting in New Orleans.

These shifting coastlines would have inundated grazing areas and farmland, and could have helped bring about the end of the Nordic way of life in Greenland, says Marisa Borreggine, a geophysicist at Harvard University.

Greenland was first colonized by Vikings in 985 by a group of settlers in 14 ships led by Erik the Red, who had been banished from neighboring Iceland for manslaughter. Erik and his followers settled across southern Greenland, where they and their descendants hunted for seals, grazed livestock, built churches and traded walrus ivory with European mainlanders.

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The settlers arrived during what’s known as the Medieval Warm Period, when conditions across Europe and Greenland were temperate for a handful of centuries (SN: 7/24/19). But by 1350, the climate had started taking a turn for the worse with the beginning of the Little Ice Age, a period of regional cooling that lasted well into the 19th century.

Researchers have long speculated that a rapidly changing climate could have dealt a blow to Greenland’s Norse society. The island probably became much colder in the last 100 years of Norse occupation, says paleoclimatologist Boyang Zhao at Brown University in Providence, R.I, who was not involved in the new research. Lower temperatures could have made farming and raising livestock more difficult, he says. 

These lower temperatures would have had another impact on Greenland: the steady expansion of the island’s ice sheet, Borreggine and colleagues say.

Though rising sea levels usually go hand in hand with ice melting from ice sheets, oceans do not rise and fall uniformly in every place, Borreggine says. Around Greenland, sea level tends to rise when the ice sheet there grows.

This is for two main reasons: First, ice is heavy. The sheer weight of the ice sheet pushes the land it rests on down, meaning that as the ice sheet grows, more land is submerged. Second is gravity. Being massive, ice sheets exert some gravitational pull on nearby water. This makes the seawater around Greenland tilt upward toward the ice, meaning that water closer to the coast is higher than water in the open ocean. As the ice sheet grows, that pull becomes even stronger, and sea level close to the coast rises further.

Simulating the impact of the weight of the ice and its tug on Greenland’s waters, Borreggine and their colleagues found that sea level rose enough to flood the coast by hundreds of meters in some areas. Between the time the Vikings arrived and when they left, there was “pretty intense coastal flooding, such that certain pieces of land that were connected to each other were no longer connected,” they say.  

Today, some Viking sites are being inundated as a result of the overall rise in global sea level from climate change, which is being only marginally offset around Greenland by its melting ice sheet. Something similar could have happened back in the 14th and 15th centuries, destroying land that the Norse relied on for farming and grazing, Borreggine says.

“Previous theories about why Vikings left have really focused on the idea that they all died because it got really cold, and they were too dumb to adapt,” Borreggine says. But they say that archaeological digs have revealed a far more nuanced story, showing that Greenland’s Norse people did change their lifestyle by increasingly relying on seafood in the last century of their occupation.

But learning to adapt may have been too difficult in the face of an increasingly harsh landscape. The idea that rising sea levels may have been one of these challenges has merit, Zhao says, noting that the reasons why the Vikings disappeared from Greenland is nuanced.

As the climate changed, for example, these people may have also found themselves increasingly cut off from trade routes as the season for thick sea ice extended. And by the mid-14th century, the Black Plague was tearing through Europe, cutting into the Vikings’ biggest market for walrus ivory.

“Norse people came and left,” Zhao says. “But there are still a lot of unsolved questions,” including why exactly they left, he says.

The last written record of this society is a letter describing a wedding in 1408. A few years later, that couple moved to Iceland and started farming. Why the pair chose to leave is lost to history, but, as the new research suggests, sea level rise may have been part of the equation.  More

NEW ORLEANS — Warmer winters could make twisters more powerful.

Though tornadoes can occur in any season, the United States logs the greatest number of powerful twisters in the warmer months from March to July. Devastating winter tornadoes like the one that killed at least 88 people across Kentucky and four other states beginning on December 10 are less common. 

But climate change could increase tornado intensity in cooler months by many orders of magnitude beyond what was previously expected, researchers report December 13 in a poster at the American Geophysical Union’s fall meeting.

Tornadoes typically form during thunderstorms when warm, humid airstreams get trapped beneath cooler, drier winds. As the fast-moving air currents move past each other, they create rotating vortices that can transform into vertical, spinning twisters (SN: 12/14/18). Many tornadoes are short-lived, sometimes lasting mere minutes and traveling only 100 yards, says Jeff Trapp, an atmospheric scientist at the University of Illinois at Urbana-Champaign.

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Over the last 20 years, tornado patterns have shifted so that these severe weather events occur later in the season and across a broader range in the United States than before, Trapp says (SN: 10/18/18). But scientists have struggled to pin down a direct link between the twister changes and human-caused climate change.

Unlike hurricanes and other severe storm systems, tornadoes happen at such a small scale that most global climate simulations don’t include the storms, says Kevin Reed, an atmospheric scientist at Stony Brook University in New York who was not involved in the study.

To see how climate change may affect tornadoes, Trapp and colleagues started with atmospheric measurements of two historical tornadoes and simulated how those storm systems might play out in a warmer future.

The first historical tornado took place in the cool season on February 10, 2013, near Hattiesburg, Miss., and the second occurred in the warm season on May 20, 2013, in Moore, Okla. The researchers used a global warming simulation to predict how the twisters’ wind speeds, width and intensity could change in a series of alternative climate scenarios.

Both twisters would likely become more intense in futures affected by climate change, the team found. But the simulated winter storm was more than eightfold as powerful as its historical counterpart, in part due to a predicted 15 percent increase in wind speeds. Climate change is expected to increase the availability of warm, humid air systems during cooler months, providing an important ingredient for violent tempests.

“This is exactly what we saw on Friday night,” Trapp says. The unseasonably warm weather in the Midwest on the evening of December 10 and in the early morning of December 11 probably contributed to the devastation of the tornado that traveled hundreds of miles from Arkansas to Kentucky, he speculates.

Simulating how historical tornados could intensify in future climate scenarios is a “clever way” to address the knowledge gap around the effects of climate change on these severe weather systems, says Daniel Chavas, an atmospheric scientist at Purdue University in West Lafayette, Ind., who was not involved in the study.

But Chavas notes that this research is only one piece of a larger puzzle as researchers investigate how tornados might impact communities in the future.

One drawback of this type of simulation is it often requires direct measurements from a historical event, Reed says. That limits its prediction power to re-creating documented tornadoes rather than broadly forecasting shifts in large-scale weather systems.

Though the team based its predictions on only two previous tornados, Trapp says he hopes that adding more historical twisters to the analysis could provide more data for policy makers as well as residents of communities that may have to bear the force of intensifying tornadoes. More

The demise of a West Antarctic glacier poses the world’s biggest threat to raise sea levels before 2100 — and an ice shelf that’s holding it back from the sea could collapse within three to five years, scientists reported December 13 at the American Geophysical Union’s fall meeting in New Orleans.

Thwaites Glacier is “one of the largest, highest glaciers in Antarctica — it’s huge,” Ted Scambos, a glaciologist at the Boulder, Colo.–based Cooperative Institute for Research in Environmental Sciences, told reporters. Spanning 120 kilometers across, the glacier is roughly the size of Florida, and were the whole thing to fall into the ocean, it would raise sea levels by 65 centimeters, or more than two feet. Right now, its melting is responsible for about 4 percent of global sea level rise.

But a large portion of the glacier is about to lose its tenuous grip on the seafloor, and that will dramatically speed up its seaward slide, the researchers said. Since about 2004, the eastern third of Thwaites has been braced by a floating ice shelf, an extension of the glacier that juts out into the sea. Right now, the underbelly of that ice shelf is lodged against an underwater mountain located about 50 kilometers offshore. That pinning point is essentially helping to hold the whole mass of ice in place.

But data collected by researchers beneath and around the shelf in the last two years suggests that brace won’t hold much longer. Warm ocean waters are inexorably eating away at the ice from below (SN: 4/9/21; SN: 9/9/20). As the glacier’s ice shelf loses mass, it’s retreating inland, and will eventually retreat completely behind the underwater mountain pinning it in place. Meanwhile, fractures and crevasses, widened by these waters, are swiftly snaking through the ice like cracks in a car’s windshield, shattering and weakening it. 

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This deadly punch-jab-uppercut combination of melting from below, ice shattering and losing its grip on the pinning point is pushing the ice shelf to imminent collapse, within as little as three to five years, said Erin Pettit, a glaciologist at Oregon State University in Corvallis. And “the collapse of this ice shelf will result in a direct increase in sea level rise, pretty rapidly,” Pettit added. “It’s a little bit unsettling.”

Satellite data show that over the last 30 years, the flow of Thwaites Glacier across land and toward the sea has nearly doubled in pace. The collapse of this “Doomsday Glacier” alone would alter sea levels significantly, but its fall would also destabilize other West Antarctic glaciers, dragging more ice into the ocean and raising sea levels even more.

That makes Thwaites “the most important place to study for near-term sea level rise,” Scambos said. So in 2018, researchers from the United States and the United Kingdom embarked on a joint five-year project to intensively study the glacier and try to anticipate its imminent future by planting instruments atop, within, below it as well as offshore of it.

This pull-out-all-the-stops approach to studying Thwaites is leading to other rapid discoveries, including the first observations of ocean and melting conditions right at a glacier’s grounding zone, where the land-based glacier begins to jut out into a floating ice shelf. Scientists have also spotted how the rise and fall of ocean tides can speed up melting, by pumping warm waters farther beneath the ice and creating new melt channels and crevasses in the underside of the ice.

To better understand the rapid retreat of Thwaites Glacier, scientists drilled a hole through the ice at the glacier’s grounding zone, the region where the land-based glacier juts out into the sea to become a floating ice shelf. Heated water (heaters shown here) carved a borehole through the ice down to the grounding zone, allowing scientists to take the first ever measurements of ocean conditions in the region.PETER DAVIS/BAS

As Thwaites and other glaciers retreat inland, some scientists have pondered whether they might form very tall cliffs of ice along the edge of the ocean — and the potential tumble of such massive blocks of ice into the sea could lead to devastatingly rapid sea level rise, a hypothesis known as marine ice cliff instability (SN: 2/6/19). How likely researchers say such a collapse is depends on our understanding of the physics and dynamics of ice behavior, something about which scientists have historically known very little (SN: 9/23/20).

The Thwaites collaboration is also tackling this problem. In simulations of the further retreat of Thwaites, glaciologist Anna Crawford of the University of St. Andrews in Scotland and her colleagues found that if the shape of the land beneath the glacier dips deep enough in some places, that could lead to some very tall ice cliffs — but, they found, the ice itself might also deform and thin enough to make tall ice cliff formation difficult.

The collaboration is only at its halfway point now, but these data already promise to help scientists better estimate the near-term future of Thwaites, including how quickly and dramatically it might fall, Scambos said. “We’re watching a world that’s doing things we haven’t really seen before, because we’re pushing on the climate extremely rapidly with carbon dioxide emissions,” he added. “It’s daunting.” More

Wildfire smoke and urban air pollution bring out the worst in each other.

As wildfires rage, they transform their burned fuel into a complex chemical cocktail of smoke. Many of these airborne compounds, including ozone, cause air quality to plummet as wind carries the smoldering haze over cities. But exactly how — and to what extent — wildfire emissions contribute to ozone levels downwind of the fires has been a matter of debate for years, says Joel Thornton, an atmospheric scientist at the University of Washington in Seattle.

A new study has now revealed the elusive chemistry behind ozone production in wildfire plumes. The findings suggest that mixing wildfire smoke with nitrogen oxides — toxic gases found in car exhaust — could pump up ozone levels in urban areas, researchers report December 8 in Science Advances.

Atmospheric ozone is a major component of smog that can trigger respiratory problems in humans and wildlife (SN: 1/4/21). Many ingredients for making ozone — such as volatile organic compounds and nitrogen oxides — can be found in wildfire smoke, says Lu Xu, an atmospheric chemist currently at the National Oceanographic and Atmospheric Administration Chemical Sciences Laboratory in Boulder, Colo. But a list of ingredients isn’t enough to replicate a wildfire’s ozone recipe. So Xu and colleagues took to the sky to observe the chemistry in action.

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Through a joint project with NASA and NOAA, the researchers worked with the Fire Influence on Regional to Global Environments and Air Quality flight campaign to transform a jetliner into a flying laboratory. In July and August 2019, the flight team collected air samples from smoldering landscapes across the western United States. As the plane passed headlong through the plumes, instruments onboard recorded the kinds and amounts of each molecule detected in the haze. By weaving in and out of the smoke as it drifted downwind from the flames, the team also analyzed how the plume’s chemical composition changed over time.

Using these measurements along with the wind patterns and fuel from each wildfire sampled, the researchers created a straightforward equation to calculate ozone production from wildfire emissions. “We took a complex question and gave it a simple answer,” says Xu, who did the work while at Caltech.

As expected, the researchers found that wildfire emissions contain a dizzying array of organic compounds and nitrogen oxide species among other molecules that contribute to ozone formation. Yet their analysis showed that the concentration of nitrogen oxides decreases in the hours after the plume is swept downwind. Without this key ingredient, ozone production slows substantially.  

Air pollution from cities and other urban areas is chock full of noxious gases. So when wildfire smoke wafts over cityscapes, a boost of nitrous oxides could jump-start ozone production again, Xu says.

In a typical fire season, mixes like these could increase ozone levels by as much as 3 parts per billion in the western United States, the researchers estimate. This concentration is far below the U.S. Environmental Protection Agency’s health safety standard of 70 parts per billion, but the incremental increase could still pose a health risk to people who are regularly exposed to smoke, Xu says.

With climate change increasing the frequency and intensity of wildfires, this new ozone production mechanism has important implications for urban air quality, says Qi Zhang, an atmospheric chemist at the University of California, Davis who was not involved in the study (SN: 9/18/20). She says the work provides an “important missing link” between wildfire emissions and ozone chemistry.

The findings may also pose a challenge for environmental policy makers, says Thornton, who was not involved in the research. Though state and local authorities set strict regulations to limit atmospheric ozone, wildfire smoke may undermine those strategies, he says. This could make it more difficult for cities, especially in the western United States, to meet EPA ozone standards despite air quality regulations. More

It’s hard to imagine what Earth might look like in 2500. But a collaboration between science and art is offering an unsettling window into how ongoing climate change might transform now-familiar terrain into alien landscapes over the next few centuries.

These visualizations — of U.S. Midwestern farms overtaken by subtropical plants, of a dried-up Amazon rainforest, of extreme heat baking the Indian subcontinent — emphasize why researchers need to push climate projections long past the customary benchmark of 2100, environmental social scientist Christopher Lyon and colleagues contend September 24 in Global Change Biology.

Fifty years have passed since the first climate projections, which set that distant target at 2100, says Lyon, of McGill University in Montreal. But that date isn’t so far off anymore, and the effects of greenhouse gas emissions emitted in the past and present will linger for centuries (SN: 8/9/21).

To visualize what that future world might look like, the researchers considered three possible climate trajectories — low, moderate and high emissions as used in past reports by the United Nations’ Intergovernmental Panel on Climate Change — and projected changes all the way out to 2500 (SN: 1/7/20). The team focused particularly on impacts on civilization: heat stress, failing crops and changes in land use and vegetation (SN: 3/13/17).

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For all but the lowest-emission scenario, which is roughly in line with limiting global warming to “well under” 2 degrees Celsius relative to preindustrial times as approved by the 2015 Paris Agreement, the average global temperature continues to increase until 2500, the team found (SN: 12/12/15). For the highest-emissions scenario, temperatures increase by about 2.2 degrees C by 2100 and by about 4.6 degrees C by 2500. That results in “major restructuring of the world’s biomes,” the researchers say: loss of most of the Amazon rainforest, poleward shifts in crops and unlivable temperatures in the tropics.

The team then collaborated with James McKay, an artist and science communicator at the University of Leeds in England, to bring the data to life. Based on the study’s projections, McKay created a series of detailed paintings representing different global landscapes now and in 2500.

The team stopped short of trying to speculate on future technologies or cities to keep the paintings based more in realism than science fiction, Lyon says. “But we did want to showcase things people would recognize: drones, robotics, hybrid plants.” In one painting of India in 2500, a person is wearing a sealed suit and helmet, a type of garment that people in some high-heat environments might wear today, he says.

The goal of these images is to help people visualize the future in such a way that it feels more urgent, real and close — and, perhaps, to offer a bit of hope that humans can still adapt. “If we’re changing on a planetary scale, we need to think about this problem as a planetary civilization,” Lyon says. “We wanted to show that, despite the climate people have moved into, people have figured out ways to exist in the climate.”

2000 vs. 2500

High greenhouse gas emissions could increase average global temperatures by about 4.6 degrees Celsius relative to preindustrial times. As a result, extreme heat in India could dramatically alter how humans live in the environment. Farmers and herders, shown in 2000 the painting at left, may require protective clothing such as a cooling suit and helmet to work outdoors by 2500, as shown in the painting at right.

If greenhouse gas emissions remain high, the U.S. Midwest’s “breadbasket” farms, as seen below in 2000 in the painting at left, could be transformed into subtropical agroforestry regions by 2500, researchers say. The region might be dotted with some versions of oil palms and succulents, as envisioned in the painting at right, and rely on water capture and irrigation devices to offset extreme summer heat.

All: James McKay (CC-BY-ND) More

Over decades, centuries and millennia, the steady skyward climb of redwoods, the tangled march of mangroves along tropical coasts and the slow submersion of carbon-rich soil in peatlands has locked away billions of tons of carbon. 

If these natural vaults get busted open, through deforestation or dredging of swamplands, it would take centuries before those redwoods or mangroves could grow back to their former fullness and reclaim all that carbon. Such carbon is “irrecoverable” on the timescale — decades, not centuries — needed to avoid the worst impacts of climate change, and keeping it locked away is crucial.

Now, through a new mapping project, scientists have estimated how much irrecoverable carbon resides in peatlands, mangroves, forests and elsewhere around the globe — and which areas need protection.

The new estimate puts the total amount of irrecoverable carbon at 139 gigatons, researchers report November 18 in Nature Sustainability. That’s equivalent to about 15 years of human carbon dioxide emissions at current levels. And if all that carbon were released, it’s almost certainly enough to push the planet past 1.5 degrees Celsius of warming above preindustrial levels.

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“This is the carbon we must protect to avert climate catastrophe,” says Monica Noon, an environmental data scientist at Conservation International in Arlington, Va. Current efforts to keep global warming below the ambitious target of 1.5 degrees C require that we reach net-zero emissions by 2050, and that carbon stored in nature stays put (SN:12/17/18). But agriculture and other development pressures threaten some of these carbon stores.

To map this at-risk carbon, Noon and her colleagues combined satellite data with estimates of how much total carbon is stored in ecosystems vulnerable to human incursion. The researchers excluded areas like permafrost, which stores lots of carbon but isn’t likely to be developed (although it’s thawing due to warming), as well as tree plantations, which have already been altered (SN: 9/25/19). The researchers then calculated how much carbon would get released from land conversions, such as clearing a forest for farmland. 

That land might store varying amounts of carbon, depending on whether it becomes a palm oil plantation or a parking lot. To simplify, the researchers assumed cleared land was left alone, with saplings free to grow where giants once stood. That allowed the researchers to estimate how long it might take for the released carbon to be reintegrated into the land. Much of that carbon would remain in the air by 2050, the team reports, as many of these ecosystems take centuries to return to their former glory, rendering it irrecoverable on a timescale that matters for addressing climate change.

Releasing that 139 gigatons of irrecoverable carbon could have irrevocable consequences. For comparison, the United Nations’ Intergovernmental Panel on Climate Change estimates that humans can emit only 109 more gigatons of carbon to have a two-thirds chance of keeping global warming below 1.5 degrees C. “These are the places we absolutely have to protect,” Noon says.

Approximately half of this irrecoverable carbon sits on just 3.3 percent of Earth’s total land area, equivalent to roughly the area of India and Mexico combined. Key areas are in the Amazon, the Pacific Northwest, and the tropical forests and mangroves of Borneo. “The fact that it’s so concentrated means we can protect it,” Noon says.

Roughly half of irrecoverable carbon already falls within existing protected areas or lands managed by Indigenous peoples. Adding an additional 8 million square kilometers of protected area, which is only about 5.4 percent of the planet’s land surface, would bring 75 percent of this carbon under some form of protection, Noon says.

“It’s really important to have spatially explicit maps of where these irrecoverable carbon stocks are,” says Kate Dooley, a geographer at the University of Melbourne in Australia who wasn’t involved in the study. “It’s a small percentage globally, but it’s still a lot of land.” Many of these dense stores are in places at high risk of development, she says. 

“It’s so hard to stop this drive of deforestation,” she says, but these maps will help focus the efforts of governments, civil society groups and academics on the places that matter most for the climate. More

This year was supposed to be a turning point in addressing climate change. But the world’s nations are failing to meet the moment, states a new report by the United Nations Environment Programme.

The Emissions Gap Report 2021: The Heat Is On, released October 26, reveals that current pledges to reduce greenhouse gas emissions and rein in global warming still put the world on track to warm by 2.7 degrees Celsius above preindustrial levels by the end of the century.

Aiming for “net-zero emissions” by midcentury — a goal recently announced by China, the United States and other countries, but without clear plans on how to do so — could reduce that warming to 2.2 degrees C. But that still falls short of the mark, U.N. officials stated at a news event for the report’s release.

At a landmark meeting in Paris in 2015, 195 nations pledged to eventually reduce their emissions enough to hold global warming to well below 2 degrees C by 2100 (SN: 12/12/15). Restricting global warming further, to just 1.5 degrees C, would forestall many more devastating consequences of climate change, as the Intergovernmental Panel on Climate Change, or IPCC, reported in 2018 (SN: 12/17/18). In its latest report, released in August, the IPCC noted that extreme weather events, exacerbated by human-caused climate change, now occur in every part of the planet — and warned that the window to reverse some of these effects is closing (SN: 8/9/21).

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Despite these dire warnings, “the parties to the Paris Agreement are utterly failing to keep [its] target in reach,” said U.N. Secretary-General António Guterres. “The era of half measures and hollow promises must end.”

The new U.N. report comes at a crucial time, just days before world leaders meet for the 2021 U.N. Climate Change Conference, or COP26, in Glasgow, Scotland. The COP26 meeting — postponed from 2020 to 2021 due to the COVID-19 pandemic — holds particular significance because it is the first COP meeting since the 2015 agreement in which signatories are expected to significantly ramp up their emissions reductions pledges.

The U.N. Environment Programme has kept annual tabs on the still-yawning gap between existing national pledges to reduce emissions and the Paris Agreement target (SN: 11/26/19). Ahead of the COP26 meeting, 120 countries, responsible for emitting just over half of the world’s greenhouse gas emissions, announced their new commitments to address climate change by 2030.

The 2021 report finds that new commitments bring the world only slightly closer to where emissions need to be by 2030 to reach warming targets. With the new pledges, total annual emissions in 2030 would be 7.5 percent lower (about 55 gigatons of carbon dioxide equivalent) than they would have been with pledges as of last year (about 59 gigatons). But to stay on track for 2 degrees C of warming, emissions would have to be about 30 percent lower than the new pledges, or about 39 gigatons each year. To hold warming to 1.5 degrees C requires a roughly 55 percent drop in emissions compared with the latest pledges, to about 25 gigatons a year.

“I’m hoping that the collision of the science and the statistics in the gap analysis, and the voices of the people will promote a greater sense of urgency,” says Gabriel Filippelli, a geochemist at Indiana University–Purdue University Indianapolis.

On October 26, Filippelli, the editor of the American Geophysical Union journal GeoHealth, and editors in chief of other journals published by the organization coauthored a statement in Geophysical Research Letters. Theyurged world leaders at COP26 to keep the “devastating impacts” of climate change in check by immediately reducing global carbon emissions and shifting to a green economy. “We are scientists, but we also have families and loved ones alongside our fellow citizens on this planet,” the letter states. “The time to bridge the divide between scientist and citizen, head and heart, is now.”

Publishing that plea was a departure for some of the scientists, Filippelli says. “We have been publishing papers for the last 20 to 30 years, documenting the train wreck of climate change,” he says. “As you can imagine, behind the scenes there were some people who were a little uncomfortable because it veered away from the true science. But ultimately, we felt it was more powerful to write a true statement that showed our hearts.” More

The kids are not all right. Children born in 2020 could live through seven times as many extreme heat waves as people born in 1960.

That’s the projected generational disparity if global greenhouse gas emissions are curbed by the amount currently promised by the world’s nations, climate scientist Wim Thiery of Vrije Universiteit Brussel in Belgium and colleagues report September 26 in Science. Under current pledges, Earth’s average temperature is expected to increase by about 2.4 degrees Celsius relative to preindustrial times by 2100. While the older generation will experience an average of about four extreme heat waves during their lifetime, the younger generation could experience an average of about 30 such heat waves, the researchers say.

More stringent reductions that would limit warming to just 1.5 degrees C would shrink — but not erase — the disparity: Children born in 2020 could still experience four times as many extreme heat waves as people born in 1960.

Scientists have previously outlined how climate change has already amped up extreme weather events around the globe, and how those climate impacts are projected to increase as the world continues to warm (SN: 8/9/21). The new study is the first to specifically quantify how much more exposed younger generations will be to those events.

An average child born in 2020 also will experience two times as many wildfires, 2.8 times as many river floods, 2.6 times as many droughts and about three times as many crop failures as a child born 60 years earlier, under climate scenarios based on current pledges. That exposure to extreme events becomes even higher in certain parts of the world: In the Middle East, for example, 2020 children will see up to 10 times as many heat waves as the older cohort, the team found.

With this possible grim future in mind, student climate activists in the #FridaysforFuture movement have been among the most powerful voices of protest in recent years (SN: 12/16/19). Thiery and colleagues note that these findings come at a crucial time, as world leaders prepare to gather in Glasgow, Scotland, in late October for the 2021 United Nations Climate Change Conference to negotiate new pledges to reduce greenhouse gas emissions. More