How high will global temperatures rise because of climate change? How hot is too hot for human health?

“Heat stress is the additive health impact of heat and humidity, which can cause an array of societal problems from reduced labor productivity to premature deaths,” said Yi Zhang, a Ph.D. candidate in atmospheric and oceanic sciences at Princeton and lead author of a paper that develops a method to accurately project extreme heat in the tropics.

This method relies on evaluating what is called “wet-bulb” temperature, which is a measure of heat and humidity that is set by the troposphere – the lower atmosphere where weather happens.

The researchers found that wet-bulb temperatures in the tropics are likely to increase by 1 degree Celsius with every degree of mean warming. Heat and humidity will stay within habitable levels if the increase in global average temperature due to climate change is limited to 1.5 or 2 degrees Celsius compared to the past 40 years.

But climate change can cause a disequilibrium in this system, by raising the bar on the wet-bulb temperature. This can cause heat and humidity in the lower layer to rise across the tropics.