Findings of a new report warn that by the end of the century, as many as 150,000 U.S. deaths could be attributed to extreme heat caused by climate change if steps are not taken to limit current carbon pollution levels.

The report, released by the Natural Resources Defense Council, assessed excessive heat in 40 cities and projected that by 2099 there will be an increase in the number of days where the heat index – how hot it feels when both the actual temperature and the relative humidity is factored – reaches between 105 and 110 degrees. These extended days of high temperature will lead to a rise in the number of heat-related deaths, according to the study.

The group’s projections indicate the number of Excessive Heat Events, or EHE, to increase five-fold by 2050, from 233 to 1,342, and eight-fold by 2099, estimating as many as 1,918 such days to occur.

Of the 40 cities studied, 37 are expected to see a rise in the number of heat-related deaths by 2099, with the largest increases being seen in Louisville with 18,000, Detroit with 17,900, and Cleveland with 16,600 fatalities. Projections for Chicago saw more than 6,300 additional deaths due to heat by 2099, despite averaging 93 fatalities a year from 1975 to 2004, totaling more than 2,600 in all.

As University of Miami Professor Dr. Larry Kalkstein explained, the socioeconomic aspects of an urban area – for example, the number of its poor and vulnerable residents - played as much of a role as a city’s geography. Kalkstein helped produce the report.  

“Much of this is cultural rather than physical in terms of the differences from city to city,” he said.

Indeed, while figures from the Centers for Disease Control and Prevention has the number of heat-related deaths in the U.S. from 1995 to 2004 at approximately 569 a year, totaling nearly 4,000 for that entire period, according to Kalkstein those numbers do not consider those who died as a result of conditions that were exacerbated by the rise in temperatures.

“It’s a well-established fact that when temperatures rise we’re going to have a more negative impact on human health,” Kalkstein said. “However, the impact of heat on human health has been historically understated.” 

On average, extreme heat has killed more people each year than flooding, lightning, tornadoes and hurricanes combined, making it the number one weather-related cause of death in the U.S., according to the National Oceanic and Atmospheric Administration.

This year, NOAA has projected above normal temperatures for much of the country throughout June, July and August, with many areas already experiencing the first signs of what is expected to come after going through one of the warmest winters on record this year. Chicago experienced record-breaking highs for two consecutive days this Memorial Day weekend and the National Weather Service predicts this will be the warmest spring in the city's recorded history.

According to NRDC Climate Program Director Dr. Daniel Lashof, the study is intended to show the potential health dangers at stake if efforts were blocked to limit the effects of the release of carbon emissions, regarded as one of the major causes for a steady rise in global temperatures over the past century, according to the U.S. Environmental Protection Agency.

Earlier this month, the EPA withdrew taking final action on the Cross-State Air Pollution Rule, which would have required power plants in 27 states to comply with new guidelines intended to reduce CO2 emissions.

The proposed regulation has been contested by a coalition composed of power companies, industry advocates, and several coal-producing states who have filed a joint lawsuit seeking to permanently do away with the new guidelines.

So far their efforts have been met with some degree of success. Last December, the U.S. Court of Appeals for the D.C. Circuit granted a stay of the rule, a move a number of legal observers at the time said could be viewed as a positive indication as to how the court may ultimately rule on the merits of the challenge.

“The health threat posed by climate change is why the EPA is responsible for setting standards to limit carbon pollution under the Clean Air Act,” Lashof said. “The EPA is charged with protecting the public health from air pollution, and they’re moving forward with doing that having proposed the first national limits on carbon pollution from power plants.”

At the local level, Kalkstein said there were several actions cities could take to prepare for excessive heat events, including establishing cooling centers for those without air-conditioning, as well as broadcast warnings when a heat event is imminent. He also recommended cities create a toll-free telephone number people can call when they experience any of the symptoms – such as dizziness or exhaustion – associated with heat-related illness. Other suggestions included making hospital emergency rooms were well staffed during excessive heat days to handle any potential influx of patients and encouraging residents to check on elderly neighbors.

Kalkstein said some cities, in particular Philadelphia and Chicago, saw modest increases in the number of heat-related mortalities compared to other places due to the level of its emergency preparedness. Chicago’s current emergency plan for extreme heat came as a result of the infamous heat wave during the summer of 1995 that killed more than 700 people. 

Writer Eric Klinenberg, author of “Heat Wave: A Social Autopsy of Disaster in Chicago”, said city officials at the time were criticized for a lack of coordination in assisting the most vulnerable residents and for an overall failure to effectively warn the public of the danger.