The United States stands to lose a lot more from climate change than it realizes.

In a study published Monday, scientists estimate for the first time how much each country around the world will suffer in future economic damage from each new ton of carbon dioxide pumped into the atmosphere. What they found may come as a surprise: the future economic costs within the U.S. borders are the second-highest in the world, behind only India.

The results suggest that the U.S. has been underestimating how much it benefits from reducing its greenhouse gas emissions and that the country has far more to gain from international climate agreements than the Trump administration is willing to admit.

"Our analysis demonstrates that the argument that the primary beneficiaries of reductions in carbon dioxide emissions would be other countries is a total myth," said lead author Kate Ricke, an assistant professor at the University of San Diego's School of Global Policy and Strategy and Scripps Institution of Oceanography.

Some smaller countries are expected to lose significantly larger portions of their economies to climate change. But the authors found, after modeling hundreds of scenarios, that the U.S. consistently faces among the costliest damages, as measured by what economists call the social cost of carbon. "It makes a lot of sense because the larger your economy is, the more you have to lose. Still, it's surprising just how consistently the U.S. is one of the biggest losers, even when compared to other large economies," Ricke said.

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The social cost of carbon is a complicated calculation that puts a price on the future damages caused by today's emissions, expressed in today's dollars. It is used by economists to suggest how much people should be willing to pay now to avoid climate damage to future generations. Its value is inherently uncertain and depends on many scientific and economic factors.

This study, published in the scientific journal Nature Climate Change, estimates the future costs to each country based on all the ways climate change currently affects economies, such as higher health and energy costs and damage to property and agriculture. But the authors stress that it's still a conservative estimate because it doesn't capture longer-term effects that are still coming, including sea level rise that will put coastal cities at risk and ocean acidification that can damage fisheries.

The results underline the inequality of climate damage and show why nations should consider—and be held accountable for—the global harm their emissions cause, and not just the impact in their own backyards.

Where the Economic Damage Falls

By looking at the economic damage on the national level, the study shows how each country's share of the global damage compares to its share of global CO2 emissions.

The U.S.'s share of the global damage, about 12 percent according to the study, is slightly less than its share of the global emissions. But India's share of the damage is four times higher than its contribution. "India is getting hit four times harder than it deserves to be based on its own emissions," said study co-author Ken Caldeira, an atmospheric scientist at the Carnegie Institution for Science.

In contrast, China's share of the emissions is four times larger than its share of the estimated damages, the study says.

The case of Russia shows how some of the major emitters could even gain from rising temperatures, as a warming Siberia would benefit Russia economically in the short term, according to the findings, (though the estimates don't account for longer-term impacts the country will face, such as damage to Arctic ecosystems and the rising ocean). Northern Europe and Canada also could have low costs or even short-term net benefits from CO2 emissions, according to the estimates.

If these countries only considered the current economic impact within their borders, they would appear to have little incentive to cut their emissions. But the longer-term effects are coming, and the study's authors point out that economic damages will spill over as other nations struggle with global warming: trade disruptions will make it harder to import goods they depend on or to export their own, the risks of global economic of turmoil and mass migration will rise, as will the potential for liability for damage caused by their years of high emissions.

If all countries acted only on their own country-level social cost of carbon, the authors calculate that only about 5 percent of the global climate externality would be internalized.

U.S. Government Estimates Are Much Lower

The U.S. government uses a social cost of carbon in its cost-benefit analyses when it designs new environmental regulations or rewrites old ones, but its numbers are much lower than those in the study.

The Obama administration set its median social cost of carbon at about $42 per metric ton for 2020. It based that on calculations of the global harm being created by each ton of U.S. emissions. When the Trump administration came in, it argued that the social cost of carbon should only address the impact on the U.S., and it wanted a higher discount rate. When the Trump administration issued its cost-benefit analysis for rolling back the Clean Power Plan, it cited numbers closer to $3 per ton.

Looking just at the impact within U.S. borders, the new study estimates the U.S. social cost of carbon emissions is nearly $48 per ton.

That wouldn't support the Trump administration's plans for weakening the Clean Power Plan and energy efficiency standards, because the estimate of just U.S. damages is close to what the Obama administration used for global impact, Ricke said.

"American policy is looking backward to a world that no longer exists," Caldeira said. "It should instead be preparing for a future that is very different from the past."

Several other countries face damages above $20 per ton. The study estimates India's localized social cost of carbon at around $86 per ton, Saudi Arabia at $47, and China, Brazil and the United Arab Emirates at $24. The global cost when the economic impact on all nations is added up is around $417 per ton.

And even those are likely to be underestimates, the authors said. The researchers used an empirical macroeconomic approach that captures all market impacts of climate change that could already be seen affecting the economy by 2014, but that doesn't capture potential catastrophic events, short-term costs of adaptation, biodiversity loss, or the longer-term impacts of sea level rise and ocean acidification.

Pinpointing Where Adaptation Needs Are Highest

One challenge with using the social cost of carbon to drive policies is that it's an uncertain number, said Noah Kaufman, a researcher at Columbia University's Center on Global Energy Policy who served in the Obama administration as deputy associate director of energy and climate change for the Council on Environmental Quality.

He noted that most Obama-era regulations that used the social cost of carbon could have been justified solely with non-climate rationales.

"Where studies like this are most useful on the adaptation side," he said. "We're going to experience some level of climate change no matter what. These help us understand which areas of the world are most vulnerable."