As the climate crisis continues, the U.S. will see heat-related deaths multiply, according to research that scientists say is a sobering reminder of the importance of adapting to rising temperatures and reining in planet-warming pollution.

Across more than 100 U.S. cities, nearly 2,000 people died each year from exposure to extreme heat or cold between 1987 and 2000, the period over which data correlated to individual cities are available. By the 2010s the number of annual deaths was closer to 12,500. And when the global average temperature reaches three degrees Celsius above preindustrial averages—which scientists have said could occur around the end of the century, given current emissions reduction plans—the annual totals will be around 63,000 deaths related to extreme temperatures, according to research published last month in GeoHealth. Most of that growth comes from deaths in extreme heat.

The research is a direct response to a talking point by climate deniers that holds that because much of the U.S. has historically been more vulnerable to cold, a warming climate isn’t concerning, says study co-author Jangho Lee, an atmospheric scientist at the University of Illinois at Chicago. “Their argument was that since there are more cold-related deaths, compared to heat-related deaths, global warming will actually benefit human health,” he says. “We did not think that was true.”

That said, focusing on the balance between cold- and heat-related deaths might not be helpful because the latter are very likely undercounted, compared with cold-related mortality, says the University of Washington’s Kristie Ebi, an epidemiologist who specializes in climate change and wasn’t involved in the new research. For one thing, she says, many hypothermia deaths “have to do with water, alcohol and boats,” not the temperature alone. In addition, Ebi says, when evaluating temperature-related deaths, scientists consider a three-week period for cold days versus just a three-day lag for hot ones. And in the U.S., extreme heat is already more deadly than hurricanes, floods and tornadoes combined.

Lee and his colleague Andrew Dessler, a climate scientist at Texas A&M University, decided to run the numbers. They considered a trio of key factors that contribute to temperature-related deaths. First, the scientists noted that the U.S. population is expected to continue growing—so it’s no surprise that total temperature-related deaths will also grow. Additionally, they considered changing demographics, particularly the fact that the country’s population is aging, and both people with illnesses associated with aging, such as heart disease, and the elderly are at higher risk of dying from either cold or heat. Finally, the researchers considered adaptation by comparing cities’ current ability to manage extreme temperatures with what could happen if, for example, one that was more accustomed to helping people manage cold winters developed responses to better help them handle extreme heat.

Lee and Dessler’s findings suggest that, up through three degrees C of warming, increasing heat deaths and decreasing cold deaths will about balance out, with increases in total mortality driven by a growing and aging population. But with more than three degrees C of warming, they find, climate change will start pushing the number of deaths even higher.

Adaptation could reduce the rise by about a quarter, however. “We were surprised by how much adaptation factors control the future temperature-related deaths, even more than climate itself,” Lee says. “So it is very important for us to adapt.” In cases of extreme heat, adaptation reduced annual deaths by nearly 10,000.

But the findings shouldn’t make people complacent about the prospect of less than three degrees C of warming, says Elisaveta Petkova, an environmental epidemiologist at Drew University, who wasn’t involved in the new research. “I don’t think we should feel completely reassured by the fact that most of those effects in the paper are projected to happen above three degrees Celsius change,” she says. “When you have rising temperatures, the weather becomes really, really unpredictable,” making it potentially more dangerous.

That means the study is yet another reminder of the importance of dramatically cutting carbon pollution before the planet reaches such exacerbated levels of warming.

Moreover, Petkova says that the analysis’s emphasis on adaptation should inspire the U.S. to put more resolute focus on preparing for our climate future. “Adaptation is absolutely critical, and it requires consistent efforts,” she says. “The political climate in the United States has been a little unstable, and there hasn’t been a continuous vision about how adaptation should be approached.”