Extreme heat waves under 1.5 degrees C and 2 degrees C global warming

Severe, extreme, and exceptional heat waves, such as those that occurred over the Balkans (2007), France (2003), or Russia (2010), are associated with increased mortality, human discomfort and reduced labour productivity. Based on the results of a very high-resolution global model, we show that, even at 1.5 degrees C warming, a significant increase in heat wave magnitude is expected over Africa, South America, and Southeast Asia. Compared to a 1.5 degrees C world, under 2 degrees C warming the frequency of extreme heat waves would double over most of the globe. In a 1.5 degrees C world, 13.8% of the world population will be exposed to severe heat waves at least once every 5 years. This fraction becomes nearly three times larger (36.9%) under 2 degrees C warming, i.e. a difference of around 1.7 billion people. Limiting global warming to 1.5 degrees C will also result in around 420 million fewer people being frequently exposed to extreme heat waves, and similar to 65 million to exceptional heat waves. Nearly 700 million people (9.0% of world population) will be exposed to extreme heat waves at least once every 20 years in a 1.5 degrees C world, but more than 2 billion people (28.2%) in a 2 degrees C world. With current emission trends threatening even the 2 degrees C target, our study is helpful to identify regions where limiting the warming to 1.5 degrees C would have the strongest benefits in reducing population exposure to extreme heat.