Deadly “Killer” Heat Threatens 30% of World’s Population –“Will Reach 74% by 2100”

 

6_29_13_hot_sun

“Lethal heatwaves are very common. I don’t know why we as a society are not more concerned about the dangers,” says Camilo Mora of the University of Hawaii at Manoa, lead author of an important new study. “The 2003 European heatwave killed approximately 70,000 people—that’s more than 20 times the number of people who died in the September 11 attacks.”

Without major reductions in emissions of greenhouse gases such as CO2, up to three in four people will face the threat of dying from heat by 2100. However, even with reductions, one in two people at the end of the century will likely face at least 20 days when extreme heat can kill, according to an analysis published in Nature Climate Change.

Dangerous heatwaves are far more common than anyone realized, killing people in more than 60 different parts of the world every year. Recent deadly heatwaves include the 2010 Moscow event that killed at least 10,000 people and the 1995 Chicago heatwave, where 700 people died of heat-related causes.

A new study by the University of Hawaii has found that 30 percent of the world’s population is currently exposed to potentially deadly heat for 20 days per year or more—and like a growing forest fire, climate change is spreading this extreme heat.

Seventy-four percent of the world's population will be exposed to deadly heatwaves by 2100 if carbon gas emissions continue to rise at current rates, according to a study published in Nature Climate Change. Even if emissions are aggressively reduced, the percent of the world's human population affected is expected to reach 48 percent.

"We are running out of choices for the future," said Camilo Mora, associate professor of Geography in the College of Social Sciences at the University of Hawaii at Manoa and lead author of the study. "For heatwaves, our options are now between bad or terrible. Many people around the world are already paying the ultimate price of heatwaves, and while models suggest that this is likely to continue, it could be much worse if emissions are not considerably reduced. The human body can only function within a narrow range of core body temperatures around 37oC. Heatwaves pose a considerable risk to human life because hot weather, aggravated with high humidity, can raise body temperature, leading to life threatening conditions."

A team of researchers lead by Mora conducted an extensive review and found over 1,900 cases of locations worldwide where high ambient temperatures have killed people since 1980. By analyzing the climatic conditions of 783 lethal heat episodes for which dates were obtained, researchers identified a threshold beyond which temperatures and humidities become deadly. The area of the planet where such a threshold is crossed for 20 or more days per year has been increasing and is projected to grow even with dramatic cuts in greenhouse gas emissions. Currently, about 30% of the world's human population is exposed to such deadly conditions each year.

 

Manoa-geography-heatwave

Numerous examples, such as the 2003 European heatwave that killed approximately 70,000 people, the 2010 Moscow heatwave that killed 10,000 people and the 1995 Chicago heatwave that killed 700 people are staggering examples of the risk to life posed by heatwaves. But beyond these highly cited examples, little was known about how common such killer heatwaves are.

The international group of researchers and students coordinated by the University of Hawaii at Manoa set out to answer that question. From over 30,000 relevant publications, the researchers identified 911 papers with data on 1,949 case studies of cities or regions, where human deaths were associated with high temperatures. From those cases, dates were obtained for 783 lethal heatwaves in 164 cities across 36 countries, with most cases recorded in developed countries at mid-latitudes. Some of the cities that have experienced lethal heatwaves included New York, Washington, Los Angeles, Chicago, Toronto, London, Beijing, Tokyo, Sydney and Sao Paulo.

When analyzing the climatic conditions for those cities, the researchers discovered a common threshold beyond which temperatures and humidities became lethal. In agreement with human thermal physiology, the threshold was such that as relative humidity increases, lower temperatures become lethal.

"Finding a threshold beyond which climatic conditions turn deadly is scientifically important yet frightening," said Farrah Powell, a UH Manoa graduate student and one of the co-authors in the study. "This threshold now allows us to identify conditions that are harmful to people. And because it is based on documented cases of real people across the globe, it makes it that more credible and relevant. The scary thing is how common those deadly conditions are already."

Thousands of people have died in India from the heatwaves in recent years. Another new study published in Science Advances found that the number of heatwaves in India killing more than 100 people increased 2.5 times between 1960 and 2009—an uptick likely due to climate change, says study co-author and University of California, Irvine professor Steven Davis. Yet India’s mean temperature has only increased 0.9 degrees Fahrenheit (0.5 degrees Celsius) in the past 50 years, a mild increase in comparison to other parts of the world.

Small increases in mean temperatures can have a major impact in tropical countries, especially amongst the poor who are extremely vulnerable, Davis notes. “In Chicago people can escape the heat, but that’s not the case for many poor people in India,” he says.

Temperature measurements reveal that summers in 92 percent of U.S. cities have become hotter since 1970. Cities in Texas and the Intermountain West are the most affected, according to data compiled by ClimateCentral. It shows summers in Milwaukee are now 2.4 degrees Fahrenheit (1.34 degrees Celsius) hotter on average, 3.3 degrees Fahrenheit (1.6 degrees Celsius) hotter in Dallas, and 3.8 degrees Fahrenheit (2.1 degrees Celsius) in Salt Lake City.

“This is what climate change means on the ground,” says Davis. Nor is it surprising there are 60 killer heatwaves a year, he added. Hotter temperatures are driving people to leave their homes and migrate. (Meet America's first official climate refugees.)

“Our attitude towards the environment has been so reckless that we are running out of good choices for the future,” says Mora of the University of Hawaii. “For heatwaves, our options are now between bad or terrible,” he adds. “Many people around the world are already paying the ultimate price of heatwaves.”

A web-application accompanying the paper allows counting, for any place on Earth, the number of days in a year when temperature and humidity exceed such a deadly threshold. For example, by 2100 New York is projected to have around 50 days with temperatures and humidities exceeding the threshold in which people have previously died. That same year, the number of deadly days for Sydney will be 20, 30 for Los Angeles, and the entire summer for Orlando and Houston.

The study also found that the greatest risk to human life from deadly heat was projected for tropical areas. This is because the tropics are hot and humid year round, whereas for higher latitudes the risk of deadly heat is restricted to summer.

"Warming at the poles has been one of the iconic climatic changes associated with the ongoing emissions of greenhouse gases," said co-author Iain Caldwell, a UH Manoa post-doctoral researcher. "Our study shows, however, that it is warming in the tropics that will pose the greatest risk to people from deadly heat events. With high temperatures and humidities, it takes very little warming for conditions to turn deadly in the tropics."

"Climate change has put humanity on a path that will become increasingly dangerous and difficult to reverse if greenhouse gas emissions are not taken much more seriously," says Mora. "Actions like the withdrawal from the Paris agreement is a step in the wrong direction that will inevitably delay fixing a problem for which there is simply no time to waste."

The Daily Galaxy via University of Hawaii at Manoa and National Geographic 

"The Galaxy" in Your Inbox, Free, Daily