200,000 Americans could die of temperature-related causes each year if global warming hits 3 C

Around 200,000 Americans may die every year if global warming raises average temperatures to 5.4 degrees Fahrenheit (3 degrees Celsius) above pre-industrial temperatures and cities don't prepare, a new study suggests. 

In 106 cities across the U.S., where 65% of the population lives, an average of 36,444 people died every year between 1987 and 2000 of temperature-related causes. Three-quarters of these deaths were in people who were age 75 or older. 

If warming reaches 5.4 F — which some climate experts warn may happen by the end of the century — and the country's proportion of elderly people increases as expected, this annual death toll could increase more than fivefold, the study predicted. This would amount to about one-third of the number of people who currently die from cancer each year in the country.  

Most of these additional deaths would occur in northern states, whose cities aren't well adapted to high temperatures.

However, cities that adapt to the heat, for instance by increasing access to air-conditioning (AC), could reduce these deaths by 28%, the authors of the study wrote in a paper published Aug. 15 in the journal GeoHealth. 

Related: This was the hottest summer ever recorded on Earth

"Climate change is going to pose a number of challenges to humanity; one of them will be temperature-related mortality," Andrew Dessler, study author and professor of atmospheric sciences at Texas A&M University, told Live Science in an email. "We expect a large increase in the number of temperature-related deaths over the coming century, due primarily to an aging population." 

If the average temperature rises less than 5.4 F, climate change will slightly decrease temperature-related deaths as fewer people will die from cold weather, the study found. 

"Climate change will affect people differently depending on where they live and how much warming we get," Dessler said. "In general, the northern U.S. will see increases in temperature-related mortality, while the southern U.S. will see fewer deaths." This is because the southern U.S. is already well adapted to hot temperatures, he said, so will be able to handle more extreme heat better than northern states.

The study has several limitations. Firstly, it doesn't address other causes of death impacted by climate change, like those tied to pest-spread diseases or major hurricanes, for instance. The authors also grouped "temperature-related deaths" together by modeling how the average number of daily deaths fluctuates in relation to changes in average daily temperatures, meaning they weren't able to specify precise causes of death, such as by heat stroke. By focusing on medium-to-large cities, it also doesn't address how warming might affect rural areas.

Nevertheless, Vivek Shandas, a professor of climate adaptation at Portland State University who was not involved in the research, told Live Science that this study reinforces the need to rapidly change infrastructure, landscapes and communities to account for hotter summers, especially in the North. This may include allowing for greater shade and movement of air in building plans, shoring up the energy grid and expanding green space and tree canopy, he told Live Science in an email. 

Although it is important to be better prepared for more extreme temperatures, it is also crucial to tackle the underlying issue of reducing emissions of carbon dioxide and other greenhouse gases to near zero to stabilize the climate, Dessler said.

"High temperatures this year have gone a long way in increasing the awareness of heat risks in the population and long-scale, cohesive policies would go a long way in helping minimize future health impacts," Stephen Fong, director for the Center for Integrative Life Sciences Education at Virginia Commonwealth University who was not involved in the research, told Live Science in an email. 

"While installing air conditioning may be an obvious short-term solution, it is more akin to a bandaid fix and we collectively need to address underlying issues including those leading to the increases in temperature," he said.