気候変動：気候目標を達成できても熱波の頻度は上昇するという予測

The tropics could be exposed to dangerously high heat levels most days, and the mid-latitudes are projected to experience deadly heatwaves every year by 2100, according to an article published online in Communications Earth & Environment. The findings suggest that CO2 emissions from human activity could drive global increases in exposure to extreme temperatures in the coming decades, even if global warming is limited to 2˚C, in accordance with the Paris Agreement.

A series of deadly heatwaves have impacted major cities in the past decade. The effects of climate change on heatwaves threaten the habitability of large areas of Earth’s land surface if greenhouse gas emissions are not curtailed. Very high temperatures pose a threat to public health, with extreme heat contributing to heat cramps, heat exhaustion, and chronic illnesses.

To predict global mean changes in temperature, CO2 concentrations, and relative humidity, Lucas Vargas Zeppetello and colleagues analysed predictions from global climate models, human population projections, and the relationship between economic growth and carbon emissions. They estimated that there is only a 0.1% chance of limiting global average warming to 1.5°C by 2100, in line with the updated Paris Climate Agreement goal. Instead, they predicted that the change in global mean temperatures will likely approach 2˚C by 2050. They projected that by 2100, many people living in tropical regions — such as India and sub-Saharan Africa — will be exposed to dangerously high heat levels during most days of each typical year. Additionally, deadly heatwaves, which are currently rare in the mid-latitudes, could happen every year in this region — located between the two tropics and the polar circles. For example, the authors predicted a 16-fold increase in the occurrence of dangerous heatwaves in Chicago, USA.

The authors suggest that without adaptation measures there may be large increases in the incidence of heat-related illnesses — particularly in the elderly, outdoor workers, and those with lower incomes — and that more ambitious targets to reduce emissions are needed.