Heat Stress Changes over East Asia under 1.5°C and 2°C Global Warming Target

Abstract

This study provides a first quantification of possible benefits of global warming mitigation through heat stress reduction over East Asia by comparing projection results between low-emission and high-emission scenarios as well as 1.5-degree and 2-degree target temperatures. Future changes in summer heat stress over East Asia were examined based on the wet-bulb globe temperature (WBGT) using CMIP5 multi-model simulations. Changes in the intensity, frequency, and duration of heat stress were analyzed in terms of area fraction across RCP 2.6, 4.5, and 8.5 scenarios and also between two selected model groups representing 1.5-degree and 2-degree warmer worlds, respectively. Severe heat stress, exceeding the 50-year return value of the present-day period, is expected to become very frequent occurring every second year over the large part of East Asia by the 2040s, irrespective of RCP scenarios. Frequency of extreme daily heat stress events was predicted to increase in a similar speed of expansion with signals emerging from the low-latitudes. The WGBT signal emergence is found to be much faster than that of corresponding temperature alone, due to the smaller variability in WBGT, supporting previous findings. The 1.5-degree warmer world would have about 20% reduction in areas experiencing severe heat stress over East Asia compared to the 2-degree warmer world, with significant changes identified over the low-latitudes. Further, compared to the transient world, the equilibrium world exhibited larger increases in heat stress over East Asia, likely due to the warmer ocean surface in the northwestern North Pacific. This suggests an important role of ocean warming patterns in the regional assessment of global warming mitigation.