Changes in population susceptibility to heat and cold over time: assessing adaptation to climate change

Abstract

BackgroundIn the context of a warming climate and increasing urbanisation (with the associated urban heat island effect), interest in understanding temperature related health effects is growing. Previous reviews have examined how the temperature-mortality relationship varies by geographical location. There have been no reviews examining the empirical evidence for changes in population susceptibility to the effects of heat and/or cold over time. The objective of this paper is to review studies which have specifically examined variations in temperature related mortality risks over the 20th and 21st centuries and determine whether population adaptation to heat and/or cold has occurred.MethodsWe searched five electronic databases combining search terms for three main concepts: temperature, health outcomes and changes in vulnerability or adaptation. Studies included were those which quantified the risk of heat related mortality with changing ambient temperature in a specific location over time, or those which compared mortality outcomes between two different extreme temperature events (heatwaves) in one location.ResultsThe electronic searches returned 9183 titles and abstracts, of which eleven studies examining the effects of ambient temperature over time were included and six studies comparing the effect of different heatwaves at discrete time points were included. Of the eleven papers that quantified the risk of, or absolute heat related mortality over time, ten found a decrease in susceptibility over time of which five found the decrease to be significant. The magnitude of the decrease varied by location. Only two studies attempted to quantitatively attribute changes in susceptibility to specific adaptive measures and found no significant association between the risk of heat related mortality and air conditioning prevalence within or between cities over time. Four of the six papers examining effects of heatwaves found a decrease in expected mortality in later years. Five studies examined the risk of cold. In contrast to the changes in heat related mortality observed, only one found a significant decrease in cold related mortality in later time periods.ConclusionsThere is evidence that across a number of different settings, population susceptibility to heat and heatwaves has been decreasing. These changes in heat related susceptibility have important implications for health impact assessments of future heat related risk. A similar decrease in cold related mortality was not shown. Adaptation to heat has implications for future planning, particularly in urban areas, with anticipated increases in temperature due to climate change.Electronic supplementary materialThe online version of this article (doi:10.1186/s12940-016-0102-7) contains supplementary material, which is available to authorized users.

Long Term Adaptation to Heat Stress: Shifts in the Minimum Mortality Temperature in the Netherlands

“…It has to be noted that the decreased susceptibility to heat over time may not only be related to climate change as suggested by Todd and Valleron (2015). Arbuthnott et al (2016) showed that decreased heat susceptibility is a process that is not only visible in the last decades, but already started a century ago, when climate change was still negligible. Ten out of eleven included papers in their study found some evidence of decreasing susceptibility for heat over time.…”

When do Indians feel hot? Internet searches indicate seasonality suppresses adaptation to heat

“…Human adaptation to heat (and cold) involves a complex set of physiological (body acclimatisation to local prevalent climate) [16][17][18], behavioural (personal, technological and cultural) [16][17][18] and psychological (habituation, expectation and preferences) [16][17][18] factors. While there is evidence for adaptation, based on spatial variations in health outcomes related to heat indicators and on few studies which analysed variation in temperature-related mortality over time in one location [19], such quantitative approaches are less applicable to low-and mid-income countries, where recent and good quality health data is usually not available.…”

Temporal trends in human vulnerability to excessive heat

“…In the past decade and a half, an increasing, but still relatively low, number of studies have examined temporal (interannual) trends and variability of human vulnerability to heat. We know of only one review article (Arbuthnott et al 2016) that has attempted to evaluate these results holistically, using relatively strict thresholds for inclusion, and a second that synthesizes several studies within the context of how trends may be used for future projections. While comprehensively assessing the collective heat impacts across studies is valuable for the reasons cited above, it is difficult, given that there is no standard for what a heat event is (Robinson 2001), and that the studies comprise different temporal periods that will feature different levels of adaptation.…”