What has more influence over future heat wave exposure: Climate change or population growth?

A new study authored by researchers from the National Center for Atmospheric Research and the CUNY Institute for Demographic Research has found that more people will be exposed to heat-related extremes, not only due to global warming but also due to population growth. But which effect is more important in determining future increase of people’s exposure?

This question was studied globally for climate model projections for the period 2061-2080 based on a moderate and high-end scenario of climate change, and for a moderate and high-end scenario of population growth. These results were compared with the period 1981-2005, representing present-day climate.

The definition of a heat wave is an important factor. In this study, a heat wave day is defined as a day that meets two thresholds: Daily mean temperature is greater than the two per cent warmest days in the present-day climate (the period 1981-2005), and maximum daily temperature exceeds 35 Celsius.

The impact of climate change dominates over population growth

The results show that the impact of climate change is a stronger determinant of exposure than demographic change in these scenarios. Exposure is quantified as the number of heat wave days times the number of people exposed to this heat, so called person-days of heat wave exposure. The moderate scenario of climate change, when compared with the high-end scenario, leads to a global reduction in exposure of over 50 per cent. The slower population growth scenario leads to roughly 30 per cent less exposure. Naturally, exposure reduction varies from one region to another. However, in almost all world regions, the impact of the climate change scenario dominates over the impact of the scenario of population growth.

Sub-Saharan Africa and South-east Asia are most vulnerable

The patterns of the spatial distribution of change in exposure are similar across all scenarios. Increases are largest in the equatorial/mid-latitude regions corresponding to the largest increase in heat wave days and high population growth areas such as India and large portions of Sub-Saharan Africa. Exposure increases in Eastern China in all scenarios, despite widespread areas of projected population loss. Across North America and Europe, increased exposure is most evident in urban areas (relative to rural).

Of all world regions, Sub-Saharan Africa and South-east Asia would benefit most from mitigating climate change to the moderate scenario compared with the high-end scenario. The absolute reduction in heat wave exposure resulting from this mitigation is largest in Sub-Saharan Africa. In relative terms, however, South-east Asia stands to gain the most, experiencing roughly five times less exposure. The smallest reductions in exposure resulting from this mitigation occur in the cooler, slower-growth regions of Europe and North America, as well as Oceania.

The article first appeared on Climate Change Post and is a digest of a scientific paper by Jones et al., 2018. Climatic Change 146: 423-437.

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