When disaster strikes, is climate change to blame? (2023)

LIn November, the spring weather in South America jumped from cold to steamy. Usually at that time of the year, people would have a barbecue in the yard, orbaking, in the lingering evening light. But on December 7, the temperature in northern Argentina, near the borders of Bolivia and Paraguay,hit 115 degrees Fahrenheit, making it one of the hottest places on Earth. The heat exacerbated a three-year drought, parching the soil and shrinking huge wheat crops before harvest.

As the Argentine government restricted wheat exports and warned people to stay indoors, a small team of scientists from around the world logged on to Zoom. They belonged to the World Weather Attribution (WWA) group, a collaboration of climate researchers founded in 2014 by Friederike Otto and Geert Jan van Oldenborgh to address a persistent, vexing question: Is climate change making extreme weather events worse and, if so, in what way? ? The group's ambitious goal is to provide clear answers almost as quickly as disaster strikes—for the public, media and policymakers, as well as for emergency managers and urban planners trying to understand how to prepare for the next severe event.

For example, just over a week after the 2021 heat dome began warming the US Pacific Northwest, the team released a careful and comprehensive assessment based on previous science. It concluded that the record-setting circumstances would have been nearly impossible without human-caused climate change, noting that temperatures "were so extreme that they lie well outside the range of historically observed temperatures." When parts of India and Pakistan suffered life-threatening heatwaves in the spring of 2022team assessedthat climate change has made a heat wave warmer and more likely. And when large parts of Pakistan were flooded last summer,group foundthat climate change could increase the amount of precipitation by as much as 50 percent.

This speed and certainty is a major advance in analyzing extreme weather events from a decade ago, when many scientists were hesitant to say how climate change might have contributed to individual events. The area has "completely changed," Otto told me from her office — the walls covered with world maps — at the University of Oxford, where she is a professor of global climate science. Fredi, as her colleagues call her, was born in Germany and is now a citizen of the United Kingdom. When she describes the history of the science of attribution, she is open: “In the beginning, people said, ‘You can't do it; the models are not good enough.'" Otto adds, "Now we know how to do it." Attributions in 2014 have been difficult and slow, in part because it can take more than a year for a scientific study to pass peer review. To address that backlog, WWA has developed a peer-reviewed methodology for quickly conducting this type of research and publishing the findings directly to the public.

Ten years ago the Intergovernmental Panel on Climate Change said the science of attribution was not yet "fit for purpose". In contrast, the IPCC 2021reportcalled the science of attribution "robust." The growing ability to say decisively how climate change is to blame could have implications for everything from insurance claims and court cases to international negotiations over which nations should pay for climate adaptation. Otto also hopes that the WWA reports will show governments why it is essential to reduce emissions. And so last December, as high temperatures scorched Argentina, Bolivia and Paraguay, Otto and the rest of the WWA went to work.

Increasing trust

One of the first studies on climate attribution that was widely cited by other scientists waspublished in 2004 in Nature. It came out about a year and a half after Europe's hottest summer in centuries, when crops failed and glaciers in the Alps shrank by as much as 10 percent andmore than 30,000 peopledied. The lead author, Peter A. Stott, a climate scientist at the Met Office Hadley Center for Climate Science and Services in England, concluded that human influence has at least doubled the chances of a record heat wave. At the time, says Stephanie Herring, a climate scientist at the National Oceanic and Atmospheric Administration, the question was considered "super in the weeds," intriguing primarily to researchers who enjoyed debating statistical probability and the physical dynamics of the atmosphere. When she began publishing the annual report on extreme events for the American Meteorological Society in 2012, "none of us expected that there would be the level of public interest that this area of ​​research ended up gaining."

Interest soared after Superstorm Sandy hit New York City and New Jersey in October 2012. Everyone wanted to know how the storm could stay so strong so far north. A report released a few months later noted that excessive Arctic sea ice had melted earlier that year, creating large areas of open water that absorbed the sun's heat, which likely contributed to Sandy's fury—though linksare still describedas just one plausible theory. Scientists tend to be conservative, tend to underestimate the impact, says Kevin Trenberth, a distinguished scientist at the National Center for Atmospheric Research. Most researchers were still reluctant to discuss how climate change might have affected a particular storm.

Advances in technology have made it easier to isolate the role of climate. In the early 2000s, few institutions had high-performance computing systems that could run climate models with large amounts of data. Today, with cloud services, researchers can do this work at home from a laptop. It is easier to combine models and run them multiple times, increasing confidence in the results. The accuracy of the models has also been improved, and their resolution has become much more precise, making them better at providing more precise information about specific locations.

As the field grew, two methods developed. One, known as probabilistic event attribution,used for assessmenthow much human behavior has contributed to the likelihood of a certain type of event, such as a heat wave, occurring. Scientists are comparing models of extreme weather dynamics with simulations of a world where climate change does not occur, discovering whether factors such as increased emissions have made an event more likely. WWAthe first study, for example, compared temperatures in five French cities during the 2015 heat wave with those of summers in the first half of the 1900s, finding that climate change has quadrupled the chance of a heat wave.

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In contrast, the conditional or "story" approach asks questions about specific incidents: Has climate change made the rainfall of a particular storm more intense? This method emphasizes thermodynamic changes, such as warmer air containing more water vapor.

Trenberth, anan early supporterapproach to the story, says that the scientific discussion of the two methodologies was initiallysarcastic. When a 2014 study by NOAA's Martin Hoerling, conducted after intense flooding in Boulder, Colorado, showed that climate change had not increased the chance of heavy rain in the region, Trenberth and his colleagues disputed the results. They said the study did not take into account warm sea surface temperatures in Mexico, which Trenberth argued added significant moisture to the atmosphere, increasing total precipitation. Hoerling replied that Trenberth was oversimplifying.Full discussionshown in a published newspaper article inNature.

Over time, both camps realized that the approaches could complement each other. "In an ideal world, you'd always do both," says Otto. "They look at the problem in different ways." Both methods have the potential to provide important information about relative risk, says Elisabeth Lloyd, a fellow at the American Academy of Sciences and Arts. Together, the analyzes could tell policymakers whether roads and bridges will need to withstand heavier rainfall and could inform emergency managers about how often in the future they might control access to those roads and bridges due to storms.

The field made further progress in 2017 after Hurricane Harvey stalled over the greater Houston area for days, dropping as much as 60 inches of rain in places, far surpassing previous records. Trenberthfoundthat super-warm ocean water in the Gulf of Mexico created more evaporation than normal, which directly led to excess precipitation. A separate analysis by Otto and her colleagues found that climate change hadadded 15 percent more precipitation. Trenberth wrote that governments in hurricane-prone regions will need to plan for major flooding, including upgrading evacuation routes, building codes and power grids.

This is exactly the kind of social and political recipe that generates sharp criticism that climate scientists should "stay the course" - research but keep quiet about the implications. Otto says that she was sometimes criticized for being too political. "But there is no such thing as a neutral scientist," she says. "The questions we ask are always influenced by our values, who finances us, where we live. Making it transparent is what makes good science – not pretending it's not happening.”

The Argentine challenge

When WWA started, it analyzed only a few events a year. Now they meet online almost every week to discuss disasters. The small team must prioritize which incidents it deems worthy of investigation. Many of its scholars volunteer their time, juggling between research or teaching jobs and other commitments.

To decide which disasters to study, scientistsestimatepotential humanitarian impacts using criteria developed by WWA for different types of events. For heat waves, factors include associated deaths and whether the affected area is densely populated or particularly vulnerable. WWA strives to take on incidents that harm many people, but also strives to cover different regions. "We don't just want to work on events in the Global North because that's where we happen to work," says Sarah Kew, a climate scientist at the Royal Netherlands Meteorological Institute. Breaking new scientific ground is also a factor, Otto says. WWA has decided not to study the Arctic blast that exposed millions of people in the US to dangerously low temperatures over the 2022 Christmas and New Year holidays because itpreviously studiedsimilar cold in North America and did not expect to find something new.

The South American heat wave caught the team's attention because it met several WWA criteria for heat waves: record temperatures occurring in very early summer in a vulnerable area. Although the first video conference to discuss the matter in late November 2022 offered some windows into the lives of the researchers — sunshine in Madrid, gloom in London — the meeting began without conversation. "We have an Argentine heat wave that has spread north," said Maja Vahlberg, who works with the Red Cross and Red Crescent Climate Center. "Is it related to La Niña?" Otto asked, referring to a circulation pattern in the Pacific Ocean that can increase the likelihood of heat waves in the Argentina region. In a quick chat, the team decided to reach out to scientists in South America for detailed information and quickly scheduled another meeting for early December. Twelve minutes after the call started, everyone logged out.

WWA works with local experts whenever possible, counting on them to know which datasets have the most comprehensive information about a region or how best to collect meteorological data there. At the meeting in early December, Juan Antonio Rivera, a climatologist from Argentina's Institute for Snow Research, Glaciology and Environmental Sciences, joined the Zoom collage from his office in Mendoza. Recent drought has affected northern Argentina, southern Brazil, Uruguay and Paraguay, he told the group, but large parts of those regions lack a dense network of weather stations. One of the first tasks would be to see what data is available to analyze how the drought has intensified over time. It could help the group dig up information that may not be easy for people living in Europe to find or may not be accessible to them due to language barriers.

The scientists on the call - some in the Netherlands wearing sweaters, others sweating in the Chilean sun - discussed options for mitigating the effects of the drought heatwave. "Every time we have a heat wave, the drought gets worse," said Anna Sörensson, a researcher at the Franco-Argentine Institute for the Study of Climate and Its Impacts, who lives in Buenos Aires. Low water levels in rivers have cut off an important agricultural export route, along with hydroelectric power generation, she said. The shipping union even contacted her for advice on designing new ships to operate in lower reaches of rivers.

The team had to define each event in a productive way. Otto later told me that for any attribution study they have to find out what they can measure. For heat waves, the group looks for temperatures above a certain threshold for a certain period. Droughts are more complex because they can be characterized in many ways—lack of rain, soil moisture, or surface water levels. A definition may require multiple measurements. “If you have very high temperatures, you have very high evaporation, so you have low stream flow, which has a huge economic impact; you can't catch it just by looking at the rain,” Otto said.

Otto asked the team if they could do something quickly and meaningfully based on temperature and precipitation alone. The group sorted out the options: Heat waves are fairly easy to analyze because many have been studied and linked to climate change. But some WWA members advocated a larger, slower drought analysis. Finally, one member asked, "Is there an option to do both?"

Rivera impressed the others with how incredible the temperatures were in his homeland. "November was the warmest November on record in Argentina," he said. The group's enthusiasm for quickly building a heat study and giving the necessary time to a more complex drought study quickly grew. "It's something we haven't done before - one study, but published in two parts," Otto reflected. Before people winked out of the video meeting and returned to their physical realities, they shared tasks that everyone would do offline.

Within weeks, scientists used five different sets of computer models to compare the characteristics of today's climate to pre-industrial conditions. They focused on the hottest one-week period in early December and found that climate change makes a heat wave 60 times more likely to occur. Temperatures in Argentina were probably about 2.5 degrees F warmer than they would normally be. Prevision researchthey suggested that this difference could increase the risk of heat-related death by more than 5.7 percent. The WWA published its findings at the end of Decemberanother steamy oneoverwhelmed Argentina. "It is important to note that these record temperatures occurred before the start of the Australian summer season, making them particularly exceptional," the group wrote.

As the team turned to their drought study, power went out in parts of Buenos Aires. Forest fires broke out across northern Argentina and neighboring Chile.

"What turns any weather event into a disaster is vulnerability and exposure," says Otto. Heat data alone does not show how much it affects people. If you don't look at scientific research and disaster response together, she says, "you just don't understand what climate change means." Latin America, for example, has high levels of inequality, with marginalized communities that aremore vulnerableto the health consequences of extreme weather conditions. Rivera recounted a meeting where desperate farmers knelt on dry ground and prayed for rain.

Although Argentina's plight has largely kept the headlines north of the equator, its impact will be felt globally. The country is a major exporter of wheat; estimated by the trade grouphalf of the wheat cropwill be lost in 2023 due to drought, and all crop losses could amount to10 billion dollars. Analysts have warned that the country's agricultural failures willfurther increasefood prices in the world.

WWA stands out in the climate research sphere for its willingness to deal directly with social factors. Otto points to a 2022 study by the WWAconducted in the African Sahelregion, which she says basically had nothing to do with the weather. The region's economy relies on rain to irrigate crops and sustain herds, but in 2021 the delayed rainy season has caused cascading food insecurity. "Even small shifts in rainfall," WWA wrote, "affect an already limited food supply." Due to large uncertainties in the datasets, the team was unable to determine whether there was a climate signal in precipitation changes, but cautioned that the region is "vulnerable to future impacts of climate change on global food crops."

Life and death

Even as the science of attribution improves, some experts argue that climate scientists are still understating their conclusions — an important factor as the field begins to move out of academia and into public processes like lawsuits. A related issue is that the evidence presented in court often lags behind the latest science. IN2021The Nature of Climate ChangeOtto and her colleagues examined 73 climate lawsuits worldwide and found that the evidence entered was 10 years out of date. "I think it takes a while for new science to filter into policy," Otto says, adding, "it should be faster."

The work of the WWA influenced at least one judgment. His study offorest fires 2019–2020in Australia concluded that climate change had a role in increasing the overall seasonal fire risk by a factor of nine. In 2021, an Australian court considered this result when it found that the New South Wales Environmental Protection Agency had failed to protect the environment by requiring the state to reduce greenhouse gas emissions.

As extreme weather conditions become more common, keeping up becomes more difficult. Last winter more than20 peopledied as a series of powerful atmospheric river storms dumped heavy rain and snow on California. WWA chose not to study flooding, in part because demand for attribution work far exceeds capacity. "It's a small community, and funding is limited," says Michael Wehner, a climatologist at Lawrence Berkeley National Laboratory.

Like WWA, Wehner and his collaborator, Kevin Reed of Stony Brook University, are trying to conduct near-real-time attribution studies. They analyzed Hurricane Ian in September 2022, while the storm was still washing over Florida. Their quick work was possible partly because they had just publishedpaperon the 2020 hurricane season, finding that climate change has caused it to be 5 percent wetter. They added Ian's conditions to their previous models. "We probably could have done it faster, but Kevin went to dinner," Wehner jokes. They decided to issue a timely statement ahead of a lengthy review process, declaring it likely that climate change added 10 percent to Ian's rainfall.

Wehner often has to turn down requests, prompting him to announce in 2022paper insidePLOS Air conditioningarguing that many attribution studies can now be considered routine and should be moved out of academia. Science has matured. "It could be operationalized," says Wehner, "as a weather forecast." Otto would welcome the change. "I really want NOAA to take this over," she says, "or Copernicus," the European Union's Earth observation program. "Not only would it allow the [scientific] community to do much more, but it would have a much more direct path into national policies."

In the US, NOAA recently started a pilot project led by David Easterling, the director of the National Climate Assessment there, to develop this type of capability. NOAA has some clear advantages: It gets real-time data from weather stations across the country and has access to climate model development at the Geophysical Fluid Dynamics Laboratory at Princeton University. Easterling hopes that, given the agency's reputation as impartial, if "NOAA starts saying, 'This event is 15 percent worse because of climate change,' that will start to change a lot of attitudes" among people who are still skeptical about climate change.

As the science of attribution continues to grow, it could play an important role in helping society prepare for greater risks, including informing building codes and highlighting the need to drastically reduce emissions, says Susanne Moser, a social scientist and consultant specializing in climate adaptation. Professional engineering associations are already moving toward adaptive designs such as levees built with wider bases so they can be taller as oceans rise. She points to California and other forward-looking statesthey learnhow to incorporate climate information into their infrastructure plans, work that will be valuable in rebuilding after the recent floods in that state.

Some countries will find it easier than others to finance such comprehensive adaptations, which is why the United Nations Climate Change Conference (or COP27) in 2022.created a "loss and damage" fund.help low-income countries, whose greenhouse gas emissions are relatively small. But there is still no definition of what counts as climate-related damage, Otto says. "What kind of evidence would you need? Who provides that?" She says further attribution work will be needed to determine international liability or compensation amounts.

During a recent video call with me, Otto said that work has become increasingly stressful. "In the beginning, it wasn't so much in the public eye—it didn't feel like that much pressure," she said. In 2021Time turned her onin its annual list of the 100 most influential people in the world. Now they recognize her when she is shopping or in her dance studio.

Applying the science of attribution might not be so daunting if the discipline had begun to grow decades ago, when climate change was alreadyknown problem, says Otto. But today her work is a race against time. "People are suffering," she says, "and they can't deal with the consequences."