![]() Here, we use the 1980 population distribution (total 4.4 billion) under the 1960–1990 mean climate (Fig. Our previous work 14 considered the 2015 population distribution under the 1960–1990 mean climate as a baseline (Extended Data Fig. Climate-related sources of harm not captured by the niche include sea-level rise 30, 31.įirst, we re-examined how relative population density varies with MAT. High temperatures have been linked to increased mortality 12, 13, decreased labour productivity 19, decreased cognitive performance 20, impaired learning 21, adverse pregnancy outcomes 22, decreased crop yield potential 9, increased conflict 23, 24, 25, hate speech 26, migration 27 and infectious disease spread 9, 28, 29. Exposure outside the niche could result in increased morbidity, mortality, adaptation in place or displacement (migration elsewhere). Here, we reassess the human climate niche, review its mechanistic basis, link it to temperature extremes, and calculate exposure outside the niche up to present and into the future under different demographic scenarios and levels of global warming. ![]() Mortality also increases at both high and low temperatures 10, 11, 12, consistent with the existence of a niche. The density of domesticated crops and livestock follow similar distributions 14, as does gross domestic product, which shares the same independently identified 14, 18 primary temperature peak (~13 ☌). Humans have adapted physiologically and culturally to a wide range of local climates, but despite this our niche 14 shows a primary peak of population density at a mean annual temperature (MAT) of ~13 ☌ and a secondary peak at ~27 ☌ (associated with monsoon climates principally in South Asia). The climate niche of species integrates multiple causal factors including combined 15 effects of physiology 16 and ecology 17. Here, we take a complementary, ecological approach, considering exposure to less favourable climate conditions, defined as deviations of human population density with respect to climate from the historically highly conserved distribution-the ‘human climate niche’ 14. From an equity standpoint, this is unethical 8-when life or health are at stake, all people should be considered equal, whether rich or poor, alive or yet to be born.Ī growing body of work considers how climate variability and climate change affect morbidity 9 or mortality 10, 11, 12, 13. But what is the human cost of climate change and who bears it? Existing estimates tend to be expressed in monetary terms 7, tend to recognize impacts on the rich more than those on the poor (because the rich have more money to lose) and tend to value those living now over those living in the future (because future damages are subject to economic discounting). Calls for climate justice highlight the vital need to address the social injustices driven by climate change 6. Even fully implementing all 2030 nationally determined contributions, long-term pledges and net zero targets, nearly 2 ☌ global warming is expected later this century 1, 2, 5. Similar content being viewed by othersĭespite increased pledges and targets to tackle climate change, current policies still leave the world on course for around 2.7 ☌ end-of-century global warming 1, 2, 3, 4, 5 above pre-industrial levels-far from the ambitious aim of the Paris Agreement to limit global warming to 1.5 ☌. These results highlight the need for more decisive policy action to limit the human costs and inequities of climate change. That person comes from a place where emissions today are around half of the global average. The lifetime emissions of ~3.5 global average citizens today (or ~1.2 average US citizens) expose one future person to unprecedented heat by end-of-century. ![]() Reducing global warming from 2.7 to 1.5 ☌ results in a ~5-fold decrease in the population exposed to unprecedented heat (mean annual temperature ≥29 ☌). By end-of-century (2080–2100), current policies leading to around 2.7 ☌ global warming could leave one-third (22–39%) of people outside the niche. ![]() We show that climate change has already put ~9% of people (>600 million) outside this niche. Here we express them in terms of numbers of people left outside the ‘human climate niche’-defined as the historically highly conserved distribution of relative human population density with respect to mean annual temperature. The costs of climate change are often estimated in monetary terms, but this raises ethical issues.
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