As climate disasters grow more costly, who should pay the bill?

First came a record-shattering, months-long heat wave, roiling Pakistan from March to May. Just a few weeks later came months of crushing, punishing rains that flooded a third of the entire country. The floods’ economic costs were staggering—about $40 billion, or more than 10 percent of the country’s annual GDP.

But these are not “natural” disasters. Just weeks after the catastrophes began in 2022, scientists showed a clear culprit: human-caused climate change, which intensified the rains by up to 75 percent and made the heat wave 30 times more likely.

To Pakistan’s leaders, those findings highlight a long-simmering frustration. “We are responsible for less than one percent of the emissions that lead to climate change,” M. Tariq Irfan, Pakistan’s environment minister, told National Geographic, “yet we are experiencing a multitude of disasters due to it.”

It is climate injustice, they say—the idea that those least responsible for climate change are bearing the worst burdens. And they’re fed up.

At this year’s U.N. climate conference in Egypt, COP27, Pakistan and a group of other frustrated developing countries are pushing to develop a pool of money for “loss and damages.” It would be a fund, financed by the developed nations most responsible for causing climate change, that would pay for climate-induced losses in countries that have done little to create the problem. The United States alone is responsible for over 20 percent of all historical global emissions of gases that cause climate change, such as carbon dioxide and methane.

Their case is bolstered by the rise in powerful “attribution” science, a new type of analysis using mostly computer modeling to pinpoint exactly how climate change worsens disasters such as heat waves, super-potent rainstorms, and sea level rise. That extra punch is often what causes the extreme harm to people and ecosystems, says Saleemel Huq, the director of the International Center for Climate Change and Development in Dhaka, Bangladesh, and a long-time climate negotiator for the country.

“These are impacts that are happening beyond our capacity for adaptation. We have entered the era of loss and damages,” he says.

To him and many others from developing countries who have seen their calls for climate justice ignored for decades, attribution puts a finer point on the fundamental moral imbalance of cause and effect. “There is no more deniability,” he says.

Over the past year, Scotland, Denmark, and a province in Belgium have contributed a few million into a fund in the name of climate justice. And after years of stalling, the U.S. and other developed countries are beginning to tentatively discuss loss and damages. The U.S. is "committed to engaging constructively," says a U.S. State Department representative.

But if there isn’t more explicit discussion of climate justice at this year’s COP27, Huq adds, “we’ll consider the meeting a failure from the start.”

Climate justice, delayed

In the early 1990s, a group of low-slung island countries including Vanuatu and Barbados banded together ahead of one of the first international climate meetings. Their small countries, they said, were at risk of drowning under rising seas—though as a group they were responsible for well under one percent of all climate change-causing greenhouse gas emissions.

To make up for that imbalance, they proposed an international insurance pool to be funded by developed countries—divided up by their relative contributions to the climate problem. The more you emitted past and present, the more you paid.

That proposal was roundly rejected by wealthier countries, which were willing to talk about how to trim emissions, or even how to fund efforts to adapt to climate change—but did not accept financial responsibility for past actions and linking that to compensation for those hurt by climate change impacts.

“Developed countries recognize their responsibility," says Doreen Stabinsky, an environmental policy expert at the College of the Atlantic in Maine. “And they don’t actually want to recognize their responsibility with respect to money.”

But the group of island nations didn’t give up. They gathered more allies facing their own steep risks from climate change, from sea level rise to extreme weather, and slowly pushed their case forward. Still, it took until 2013, more than 20 years later, before the concept was officially included in international climate treaties. At COP19 in Poland, the concept was labeled “loss and damages,” which referred to the costs, both economic and social, from climate-fueled problems beyond the realm of adaptation.

After a few more years of fierce negotiations, loss and damages got a paragraph in 2015’s landmark Paris Agreement—but only a promise to discuss the topic. Then, at 2021’s meeting in Scotland, negotiators asked explicitly to set up a fund for loss and damages. Once again, the meeting ended with only promises to talk more.

“For quite some time, developing countries have been going to the [climate meetings] and being gaslit,” says Adelle Thomas, a climate policy expert at the University of the Bahamas.

“Like, being told this isn’t really happening, or you can’t prove it’s due to climate change, et cetera. But now the evidence is overwhelming,” she says. “It has become irrefutable that loss and damages are happening.”

Clear moral and scientific arguments

After a 2003 heat wave in the U.K. killed over 2,000 people, a group of British researchers asked: Can we tell if human-caused climate change affected the disaster? And if so, could people sue emitters for the damages caused? After careful analysis, they figured out the answer to the first question, at least, was yes; for the first time ever, they could attribute human influence to a weather event.

For decades, scientists had known climate change was probably affecting weather, but they couldn’t say that any single incident was worsened by it: Computer models that simulated global climate weren’t yet precise enough to mimic individual weather events. But since the British research in 2003, that has changed, thanks to more powerful climate models and scientific advancements linking global climate patterns with local weather.

In its simplest terms, attribution compares the likelihood of, or intensity of an event—a storm, a heat wave, a flood caused by melting glaciers—in a theoretical world untouched by climate change versus the real one. The difference between those two is the “attributable” impact of climate change. Such modeling techniques are so sophisticated they can even analyze the impacts of slower-onset phenomena, such as sea level rise or heat-induced agricultural losses.

“The clarity with which we can explain just how climate change is affecting things has improved vastly,” says Rupert Stuart-Smith, a climate and law expert at Oxford University. For example, scientists can say that the hottest days during the Pacific Northwest’s 2021 heat wave were nearly 4 degrees Fahrenheit hotter, or that Hurricane Harvey dumped an extra 15 percent more rain on Houston, than if climate change were not present.

There are limits to attribution’s power, though—and often those limits follow the outlines of historical injustices. The technique requires good models of regional climate and weather, which require solid historical data, such as daily weather observations. Because so much scientific expertise has been centered in the Global North, sometimes it’s harder to do in places without reliable weather records, says Mariam Zachariah, a climate scientist with the World Weather Attribution program who worked on this year’s Pakistan analyses.

Nonetheless, “the science really initiates the conversation” about injustices, she says: Just look at Pakistan. After the floods, the U.N. Secretary General called for “massive financial support to overcome this crisis.” It is “not a matter of generosity, it’s a matter of justice,” he said.

Attribution in action

While attribution has made huge technical leaps, how to use the science is still hotly debated.

In the logically simplest form, some suggest that if an attribution study shows Pakistan’s rainfall was 75 percent beyond what should have been, the damage from that excess water—once counted up—should be split between those responsible, e.g. developed countries. A country like the U.S., which has contributed about 25 percent of all human-caused greenhouse gas emissions since the start of the industrial revolution in the 1850s, might be accountable for 25 percent of the costs. American oil-producing companies such as Chevron and Exxon each account for over 3 percent of all emissions since then.

But in practice, assigning a split is extraordinarily complicated. Many big emitters, either countries or corporations, say that their contributions to climate change aren’t necessarily the same as their responsibility to fix it. And social science research has shown that they balk at the idea of blame associated with attribution, making them less likely to want to talk about how to fix the problem, says Rachel James, a climate expert at the University of Bristol in the U.K.

Many big emitters have also argued that it is impossible to directly link their specific emissions with any particular outcome or event, since gases like carbon dioxide quickly spread around the atmosphere and so any given molecule’s origin can’t be traced.

Recent analyses are breaking down that argument. In August, a team from Dartmouth showed they could link the historical emissions of any country with economic damages caused elsewhere. The U.S.’s emissions from 1990 onward—two years after climate scientist James Hansen testified to Congress that human-caused climate change was clearly happening—cost the rest of the world $1.8 trillion in damages, they found. And that’s probably an underestimate.

“Emitters can no longer hide behind a veil of plausible deniability,” says Callahan, a climate researcher at Dartmouth and the lead author of the study. “Individual emitters can be held quantifiably to damages caused.”

“We’ve had the science for decades now… we have the strongest possible evidence that this is due to human activity,” and the main culprits are well known, says Thomas, of the University of the Bahamas. Now, it’s an ethical, social, and political debate.

“The question now is, how are we going to deal with this?”