Scientists Warn Climate Change Will Increase Dangerous Heat Days

Jul 16, 2019

Rising temperatures from global warming will more than double the number of dangerously hot days across the United States by 2050 unless the country does more to fight the problem. That's according to the Union of Concerned Scientists, which says the Southeast could see the biggest effects of rising temperatures.

The Union of Concerned Scientists calculated the number of high "heat index" days per year -- when a combination of high temperatures and high humidity  increase health risks.  They found that without global action to fight climate change, the number of days that feel hotter than 100 degrees Fahrenheit would increase from 14 to 36 in the U.S.  In the Southeast, the number would rise from 15 days to 65 days. 

Lead author and climate scientist Kristina Dahl said officials should be doing more to reduce carbon emissions now and preparing for inevitable higher temperatures later. 

"If we fail to reduce our heat trapping emissions  across the U.S., we would see a staggering increase in dangerous levels of heat," Dahl said in an interview.  

The report pulled together predictions about global temperature increases from 18 scientific sources, Dahl said. Those temperatures were used to calculate several scenarios for "heat index" increase -- if we do nothing, if changes are adopted slowly and if changes are adopted rapidly. 

The report presents the potential number of  90-degree-plus, 100-degree plus and 105-degree-plus heat index days under those three scenarios, as well as one titled "off the charts." 

Heat-related illness is the biggest concern, especially among children, seniors and outdoor workers. Higher temperatures also could affect infrastructure and farm productivity.  

All the scenarios foresee an increase in the number of dangerous heat days, though the sharpest rise would come if there's no action to reduce fossil fuel emissions. 

People of color and those with low incomes also will be hit hard, because they lack access to transportation, air conditioning, and health care, among other things. 

The number would not rise as quickly if there's rapid action, or even slow action, according to findings reviewed by other scientists and published Tuesday in the journal Environmental Research Communications.

North Carolina currently has an average of eight days a year with a heat index over 100. That would go up to 45 days a year by mid-century and 76 by the end of the century without action.  But if steps are taken that limit global warming to 2 degrees Celsius above pre-industrial levels, as called for in the Paris Climate Accord, the average would be just 33 a year. 

With no action, parts of Florida and Texas would have the equivalent of five months a year of 100-plus heat-index days. 

The report, titled "Killer Heat in the United States," is available at UCUSA.org