An adaptability limit to climate change due to heat stress

Abstract

Despite the uncertainty in future climate-change impacts, it is often assumed that humans would be able to adapt to any possible warming. Here we argue that heat stress imposes a robust upper limit to such adaptation. Peak heat stress, quantified by the wetbulb temperature T W , is surprisingly similar across diverse climates today. T W never exceeds 31°C. Any exceedence of 35°C for extended periods should induce hyperthermia in humans and other mammals, as dissipation of metabolic heat becomes impossible. While this never happens now, it would begin to occur with global-mean warming of about 7°C, calling the habitability of some regions into question. With 11-12°C warming, such regions would spread to encompass the majority of the human population as currently distributed. Eventual warmings of 12°C are possible from fossil fuel burning. One implication is that recent estimates of the costs of unmitigated climate change are too low unless the range of possible warming can somehow be narrowed. Heat stress also may help explain trends in the mammalian fossil record.climate impacts | global warming | mammalian physiology | paleoclimate

Long-term projections and acclimatization scenarios of temperature-related mortality in Europe

“…S5). In addition, we expect that coefficient R warm decreases in parallel with temperature rise, as human adaptability is subject to nonlinearities and limits imposed by heat stress 20 . Despite these considerations, the degree of adaptation of societies to warmer climate conditions is an issue subject to huge uncertainties 4 , and this general lack of knowledge is here solved by exploring the whole range of scenarios providing hypothetical acclimatization pace levels.…”

“…The T/M dependency in a region, area or country was estimated as follows. The range of observed temperatures was divided into equally spaced intervals 15,17,20 . Days belonging to each interval were grouped and daily temperature and mortality data within each interval averaged (circles in Supplementary Fig.…”

“…S4). Given the nonlinear dependency between temperature and mortality 4,31,32 , especially for the most extreme warm temperatures 20 , the T/M relationship was defined as a polynomial of order 3. For each tail of a given area, the optimal coefficients {a 0 , a 1 , a 2 , a 3 } from were found by means of a least squares fitting of interval mean temperature and mortality data.…”

“…Under a hypothetical extremely severe warming scenario of + 7 °C or more (for example, climate sensitivity has a 5% chance to exceed this value 19 ), heat stress would, however, start to impose a limit to human adaptability in some regions where metabolic heat dissipation would, for the first time, become impossible 20 . These constraints to human adaptability further stress the need for mitigation strategies contributing together with adaptation plans to tackle the problem of climate change 21 .…”

Fat-Tailed Uncertainty in the Economics of Catastrophic Climate Change

“…A recent article calculated that global average temperature increases of 11-12 C would cause conditions under which more than half of today's human population would be living in places where there would be periods (at least once a year) when death from heat stress would ensue after about six hours of exposure. 6 As noted, the "standard" BCA damages function reduces welfare-equivalent consumption by a quadratic-polynomial multiplier. This essentially describes a single-attribute utility function, or, equivalently, a multi-attribute utility function with strong substitutability between the two attributes of consumption and temperature change.…”