Most people are familiar with the environmental impacts of climate change, including increased temperatures, extreme weather, rising oceans, extended drought seasons and major habitat disruptions for plants and animals. But the effects of global warming reach beyond the natural world: climate change has slowed progress toward narrowing the gap in income inequality between the world’s richest and poorest nations, a new study in The Proceedings of the National Academies of Sciences shows.

To investigate, researchers examined 50 years of annual temperature data as well as GDP from 165 countries during the same time period. By looking at 20 different climate models, the team determined how much each nation had already warmed between 1961 to 2010. The team also calculated 20,000 versions of what a nation’s economic output would have been if climate change was not a factor.

The estimates show that temperature increases have had a clear-cut effect, especially on tropical nations. “For most countries, whether global warming has helped or hurt economic growth is pretty certain,” co-author Marshall Burke of Stanford says in a statement. “There's essentially no uncertainty that they’ve been harmed.”

Alejandra Borunda at National Geographic reports that the study relies on previous work by Burke that shows a strong relationship between temperature and economic productivity. Areas where the mean temperature hovers around 55 degrees were the most productive. Falling above or below that peak, the team found, had a significant impact on economies with nations averaging higher than 68 degrees being particularly affected. Researchers aren’t sure why the relationship holds, but warmer weather may make it more difficult for people to work or may lead to reductions in agricultural output.

According to the data, global warming has decreased the wealth of individuals in the world’s poorest countries by 17 to 31 percent. Meanwhile, the world’s richest countries, which are responsible for pumping greenhouse gases into the atmosphere, have benefitted from temperature increase. Most wealthy nations became roughly 10 percent richer over the same time period. Overall, the gap between Earth’s wealthiest and poorest nations is 25 percent larger than it would be without warming.

“Researchers and policy makers have been saying for many years that the greatest, most acute impacts of global warming are falling on populations least responsible for creating that global warming,” lead author Noah Diffenbaugh, also at Stanford, tells Phil McKenna of Inside Climate News. “We have quantified the effect."

Warming for many economically powerful nations in the temperate region, including the United States, China and Japan, has pushed them into the perfect temperature ranges for economic output. Norway’s GDP, on the other hand, has grown an extra 34 percent due to warming and Iceland's economic output is double what it would otherwise have been. That won’t last, the author’s warn, as temperatures increase over the next few decades.

On the down side, India’s GDP is about 30 percent lower today than it would have been without rising global temperatures. Diffenbaugh tells McKenna that’s on the same order of magnitude as the impacts of the Great Depression in the United States. Lydia DePillis at CNN reports that Costa Rica, which according to the study has experienced a 21% lower GDP, has seen lower yields of coffee and more disease among the crop all due to increasing temperatures.

“In some parts of the country their harvests have been undermined gradually, year after year after year,” says Rebecca Carter, deputy director of the climate resilience practice at the World Resources Institute.

University of California, Berkeley economist Solomon Hsiang, who also studies temperature’s impact on GDP, tells Warren Cornwall at Science that he disagrees with some of the team’s calculations, however. For example, Hsiang tells DePillis at CNN that if the authors looked at economic impacts over five year periods instead of year over year, the economic disparities disappear from the data.

But in general, Hsiang thinks the study is a good starting point for discussing the way climate change fueled by wealthier nations is disproportionately impacting poorer countries. “The study’s statement that warming should have already harmed economic opportunities in poor countries is extremely important,” he says.

In fact, some nations affected by rising sea levels and increased temperatures have begun lobbying for climate reparations, in which the wealthier nations responsible for climate change aid those nations suffering the droughts, floods, heat waves and lost coastlines.