More than six billion people encountering more exposure to extremes with 1.5 °C and 2.0 °C warming

The Paris Agreement established the aims for global warming in the 21st Century relative to preindustrial times, with 1.5 degrees C as ideal object and 2.0 degrees C as upper boundary. Compound population exposure to precipitation and temperature extremes under different warming levels, which is determined both by climate changes and changes in the amount and distribution of population, is not well known. Here, we investigate changes in population exposure to wet, dry, heat and cold extremes with 1.5 and 2.0 degrees C warming. Results show that population exposure to wet, dry and heat extremes over middle Africa, Arabian Peninsula and South Asia is generally found to increase at 1.5 and 2.0 degrees C warming levels, whereas that over eastern Asia largely decreases from 1.5 to 2.0 degrees C warming due to a population reduction by 107 million. Then we adopt a 4-bit binary number as a compound index to represent the size of the exposure increase to different extremes under different warming levels. Total population with exposure increases to wet, dry, heat and cold extremes is 2358, 1900 and 1569 million persons at 1.5 degrees C warming, 2.0 degrees C warming and from 1.5 to 2.0 degrees C warming, respectively. Furthermore, there are 7242, 6574 and 6299 million persons faced with increased exposure to all four extremes but the cold extreme during the above periods, which is more than two-thirds of total population. Thus, we should do more to face possible climate risks under global warming.