Climate tipping points—climate system changes that become self-perpetuating—throw a monkey wrench into predictions about climate change impacts. Slowing circulation in the Atlantic Ocean, which would lower global temperatures, could be one such tipping point. Global cooling could upset who wins and who loses economically from climate change over the next century, according to a study by Esteban Rossi-Hansberg, Energy Policy Institute at the University of Chicago (EPIC) scholar and Glen A. Lloyd Distinguished Service Professor in the Kenneth C. Griffin Department of Economics.
“There’s a lot of media attention to what might happen with a collapse of circulation in the Atlantic,” says Rossi-Hansberg. “With collapse an ever more likely outcome, we could see advanced economies emerge as the big losers.”
Ocean circulation linked to global climate
Global circulation in the ocean is driven by water temperature and salinity. In the North Atlantic Ocean, water cools and becomes saltier and denser. This relatively dense water sinks to the deep ocean, drawing warmer water northward.
This pattern of circulation is called the Atlantic Meridional Overturning Circulation (AMOC). It’s responsible for keeping much of Europe warmer than other places at the same latitude. Rome and Chicago, for instance, are at similar latitudes, but the former is about 10°C (18°F) warmer than the latter in winter.
Evidence that the AMOC is slowing down is mounting. Climate scientists predict this could lead to cooling temperatures over large parts of the globe. Colder regions get even colder, while warmer ones mostly stop warming or get cooler. Concern for impacts in Europe is particularly high because of how atypically warm the AMOC keeps the continent.
Cooling swaps climate winners and losers
When considering global warming alone, countries in the Global South—which are also generally warmer—face the brunt of negative future climate impacts. But higher-income, and generally cooler, countries may even benefit.
“What we found completely reverses this projection,” says coauthor Klaus Desmet, Altshuler Professor of Cities, Regions and Globalization at Southern Methodist University. “Global cooling means colder regions get even colder, while warmer ones cool. This pushes high-income countries out of temperature ranges that are more comfortable and allow for more productivity. At the same time, it also pushes currently low-income countries closer to these more comfortable and productive temperatures.”
Collapse of the AMOC induces cooling of up to 4°C (7°F) over much of the Northern Hemisphere under moderate emissions. In the Southern Hemisphere, most areas could stay at current temperatures or get cooler. Only some regions of Argentina are projected to grow warmer, as well as parts of the Southern Ocean and Antarctica.
This widespread cooling reverses the pattern of economic impact. By 2200, under moderate emissions, high-income countries in Europe could experience a 3.3 percent loss in welfare, with more than a 20 percent loss in more northern locations such as Russia and Scandinavia.
Regions that would have otherwise experienced warming and loss of welfare are predicted, under this modeling, to have increased welfare. This could amount to a 1 percent to 5 percent increase in welfare in North Africa, parts of South America and Southeast Asia.
Despite reversing some of the effects of global warming, an AMOC collapse lowers overall welfare by 1.9 percent in 2200 relative to a world that experiences global warming but no collapse.
Migration is a key adaptation to climate change
Rossi-Hansberg and his co-authors show that cooling leads to migration. By 2200, the coldest parts of Europe—Scandinavia and Russia—lose more than 25 percent and 17 percent of their populations, respectively.
The rest of Europe loses 7 percent and North America 4 percent, while the Middle East, Africa and Latin America gain up to 2 percent. Population losses are mirrored by losses in GDP of similar magnitude.
Rossi-Hansberg and his coauthors also modeled outcomes if migration were restricted. This resulted in an additional global welfare decrease of 2 percent, which demonstrates the importance of migration as a strategy for climate change adaptation.
High-resolution spatial models enable insight
Climate impacts vary spatially, across regions and countries, but also within them. That’s why Rossi-Hansberg and coauthors designed their spatial model with a high resolution. It can predict climate impacts with more detail than simply looking at regional or national differences.
“Spatial economics thinks about the relationship of the distribution of economic activity to outcomes,” says Rossi-Hansberg. “Particularly when we are considering a global phenomenon like climate change, costs and benefits are not evenly distributed. They vary across space, and our models help us understand these variations and their impact on aggregate outcomes.”
When applied to the question of a major climate tipping point, high-resolution spatial models improve our predictions of the complex, long-term impacts of climate change that have implications for climate action now.