Too Humid to Handle
Chris Manktelow discusses how areas of extreme heat and humidity are already reaching the limits of human tolerance
New research has found that extreme climate conditions are already reaching the limits of human tolerance in parts of South Asia and the Middle East. The results suggest that millions of people could be exposed to potentially deadly levels of extreme humidity and heat if the Earth’s climate continues to warm.
When we get hot, the body produces sweat which cools us down as it evaporates. But humans have their limits. In very hot and humid conditions where the air is already full of water vapour, evaporation slows down and eventually stops. This happens when the wet-bulb temperature, which is a measure of both heat and humidity, reaches 35°C. A perfectly healthy person sitting in the shade will not survive for more than a few hours in these circumstances. Even lower wet-bulb temperature readings can be deadly, especially for the elderly or for people with underlying health conditions. The 2003 heatwave in Europe provides an example of this, with thousands of people killed, despite the wet bulb temperature never reaching above 28°C.
A perfectly healthy person sitting in the shade will not survive for more than a few hours in [a wet-bulb reading of 35°C]
Previous research has projected that wet-bulb temperatures might reach the limits of human tolerance in parts of South Asia and the Middle East by the end of the 21st century. However, these simulations only looked at large areas over several hours. This can mask local, short-term variations in wet bulb temperature. A new study from Columbia University has zoomed in closer to the issue by analysing data recorded at over 7000 weather stations between 1979 and 2017.
This new study found that extreme humid heat events occur twice as often as they did almost 40 years ago, and that the severity of these heat events is increasing. The scientists also used the new data to simulate what might happen in the future if we do nothing to reduce our greenhouse gas emissions. They found that instances of extreme humid heat might regularly exceed the limits of human tolerance in parts of South Asia and the Middle East with less than 2.5°C of warming since pre-industrial times. This level could be reached within the next four to five decades.
This new study found that extreme humid heat events occur twice as often as they did almost 40 years ago
The results suggest that the challenge posed by such extreme conditions is worse than previously reported. It underscores the need for us to reduce our greenhouse gas emissions to avoid exposing millions of people to deadly levels of extreme humid heat.