The US could end up as full of hot air as the politicians sceptical of climate change. By the end of the century, heatwaves caused by global warming could kill 150,000 people who would otherwise live.

A report by the US Natural Resources Defense Council (NRDC) estimates how many extreme heat events will hit the US this century, assuming greenhouse gas emissions continue on their current path.

Climate models suggest that by 2099 the 40 most populous cities will have approximately eight times as many days of extreme heat per year as today.

About 1330 Americans die each year from extreme heat events. That figure will rise to about 4600 by 2099, giving a total of more than 150,000 extra deaths by the end of the century, according to the report – Killer Summer Heat: Projected death toll from rising temperatures in America due to climate change.

The figure may actually be an underestimate, because the US population is ageing and older people are more vulnerable to heat. Louisville in Kentucky will be the worst affected city, with an extra 19,000 deaths by 2099.

The European heatwave of 2003 killed 35,000 people, so the report's estimate is "not unrealistic", says Andreas Sterl of the Royal Netherlands Meteorological Institute in De Bilt.

Cities can use forecasting systems to warn people of imminent heatwaves and protect at-risk residents, says the NRDC's climate and clean air campaign director Peter Altman. "But no preventive measures can keep up with the added risk due to rising temperatures, so the other solution is to reduce the pollution driving climate change."

This March was the warmest on record for the lower 48 states, and temperatures continue to be high, according to the National Oceanic and Atmospheric Administration's National Climatic Data Center.