Iain Caldwell: Our study found that the vast majority of past heat-related deaths were associated with periods of high temperatures and high humidity, and that such deadly conditions could become much more common in the future, particularly in the tropics and if current carbon emissions are not reduced considerably.
By 2100, for instance, NY is likely to experience around 50 days a year with combined temperature and humidity exceeding the threshold at which people have previously died, researchers said.
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, they said.
It's hard to say how many more deaths will occur as a result of the extreme heat; that depends on how human societies deal with the problem.
"Warming at the poles has been one of the iconic climatic changes".
Deadly heat waves like the one now broiling the American West are bigger killers than previously thought and they are going to grow more frequent, according to a new comprehensive study of fatal heat conditions.
"With high temperatures and humidities, it takes very little warming for conditions to turn deadly in the tropics", said Mora. 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.
Jitendra Murmu, another daily-wage worker, said efforts to move work to cooler parts of the day were becoming less effective. "The problem with humidity is that is makes lower temperatures lethal", Mora said. We were also able to identify a threshold in these two conditions, beyond which the combination and temperature has been lethal in the past.
Mora, the author of the University of Hawaii study, noted that the impacts of rising heat will extend far beyond simply a higher death toll, to things like "people having to take longer breaks to withstand the heat and compensate for it by working longer hours". Unless global warming is dealt with, those numbers will increase and heat wave deaths will become even more common.
Mora and his team, made up by a group of global researchers and students, looked at more than 30,000 relevant publications to find data on 1,949 case studies of cities or regions in which human deaths were linked to high temperatures.
Heat waves are already killing people around the globe today, in incidents including the 2010 Moscow event with its at least 10,000 casualties, as well as in the last few weeks in India and Pakistan where dozens died. Mora explained that not only high rise of temperatures but also moderate rise in temperatures of less than 86 degrees Fahrenheit (30 degrees Celsius) when combined with high humidity can lead to deaths.
For the analysis published in the journal Nature Climate Change, Mora's team pored over more than 30,000 publications to find data on nearly 2,000 case studies of places with heat and human death links.
"Our attitude towards the environment has been so reckless that we are running out of good choices for the future". "For heatwaves, our options are now between bad or awful".