Global and regional changes in exposure to extreme heat and the relative contributions of climate and population change

Abstract

The frequency and intensity of extreme heat wave events have increased in the past several decades and are likely to continue to increase in the future under the influence of human-induced climate change. Exposure refers to people, property, systems, or other elements present in hazard zones that are thereby subject to potential losses. Exposure to extreme heat and changes therein are not just determined by climate changes but also population changes. Here we analyze output for three scenarios of greenhouse gas emissions and socio-economic growth to estimate future exposure change taking account of both climate and population factors. We find that for the higher emission scenario (RCP8.5-SSP3), the global exposure increases nearly 30-fold by 2100. The average exposure for Africa is over 118 times greater than it has been historically, while the exposure for Europe increases by only a factor of four. Importantly, in the absence of climate change, exposure is reduced by 75–95% globally and across all geographic regions, as compared with exposure under the high emission scenario. Under lower emission scenarios RCP4.5-SSP2 and RCP2.6-SSP1, the global exposure is reduced by 65% and 85% respectively, highlighting the efficacy of mitigation efforts in reducing exposure to extreme heat.

Projections of Human Exposure to Dangerous Heat in African Cities Under Multiple Socioeconomic and Climate Scenarios

“…We further investigated the individual effect of changes in socioeconomic and climatic conditions by disaggregating the exposure projections into the climate, population, and interaction effects. Existing studies on heat exposure under the SSPs—which focused on the global or regional levels—all found the population effect to be significant, although more often than not lower than the climate and interaction effects (Asefi‐Najafabady et al, ; Coffel et al, ; Jones et al, ; Liu et al, ). Here we corroborate the significance of the population effect and demonstrate that it is much higher than the climate effect alone—and of same magnitude as the interaction effect—in the context of African cities.…”

“…Although some recent studies have considered only maximum temperature to define the heat index ( HI ) without accounting for humidity, for example (Dong et al, ; Harrington & Otto, ; Liu et al, ), evidence suggests that humidity plays an important role in temperature discomfort and dangerous heat and thus must be integrated into the construction of the HI (Coffel et al, ; Davis et al, ; Matthews et al, ; Mora et al, ), particularly in South America, Africa, and South Asia (Russo et al, ). Various heat metrics that include both temperature and humidity have been developed over the past few years, all performing well and rather similarly (Anderson et al, ; Matthews et al, ).…”

“…Driven by both high population growth and significant changes in climatic conditions, future exposure to dangerous heat in Africa is projected to show the highest increase worldwide during the 21st century, with South Asia being close behind (Coffel et al, 2018;Dong et al, 2015;Jones et al, 2018;Liu et al, 2017;Matthews et al, 2017). Recent regional studies conducted in Eastern Africa (Harrington & Otto, 2018) and across the Great African Lakes region (Asefi-Najafabady et al, 2018) have provided a closer look at the effects of changes in socioeconomic and climatic conditions on future exposure to dangerous heat in some parts of Africa.…”

Analyzing Regional Climate Change in Africa in a 1.5, 2, and 3°C Global Warming World

“…The mean annual HN, the mean annual HWD, and HWs affect the human health and the human mortality and can thus be assigned to the health sector (Liu et al, 2017;Patz et al, 2005;Phalkey & Louis, 2016;Schmitt et al, 2016). For the 1.5 and 2°C global warming scenario the model ensemble projects a moderate to strong increase in mean annual HN and for the 3°C global warming scenario a very strong increase in mean annual HN for central Africa (15°S-15°N).…”

Projected Heat Stress Under 1.5 °C and 2 °C Global Warming Scenarios Creates Unprecedented Discomfort for Humans in West Africa

“…Such temperature increase is expected to continue in the future with a projected global temperature change of about 1.4°C to 4.8°C (Intergovernmental Panel on Climate Change, 2014) and a regional response over the Sahel of about 2°C to 6°C (Sylla, Nikiema, et al, 2016) when considering the Representative Concentration Pathway 4.5 and 8.5 concentration scenarios (Moss et al, 2012). As a result, hot extremes will become more common and deadly in many regions across the world (Gasparrini et al, 2017;Im et al, 2017;Lee & Kim, 2016;Mora et al, 2017) and in tropical Africa (Giorgi et al, 2014;Liu et al, 2017;Russo et al, 2014), with their frequency, duration, and magnitude depending on the underlying forcing scenario (Anderson et al, 2018;Dosio, 2017;Linares et al, 2014;Russo et al, 2016). Such hot extremes can have widespread impacts on human and natural systems, thereby challenging the adaptive capacity and resilience of local populations and activities (Ceccherini et al, 2017;Fontaine et al, 2013;Pal & Eltahir, 2016;Sultan & Gaetani, 2016;Zougmoré et al, 2016).…”