Future of the human climate niche

18.05.2021

Несмотря на то, что сегодня люди живут в различных климатических условиях, на деле абсолютное большинство из них предпочитают жить на территориях со среднегодовой температурой около 13 градусов. Однако изменение температуры даже в 1 градус может вынудить мигрировать 1 млрд человек. Значительные территории Земли не подходят для жизни, и, похоже, что их площадь будет увеличиваться из-за глобального потепления. PNAS подготовили статью о возможных угрозах глобального потепления

Significance

We show that for thousands of years, humans have concentrated in a surprisingly narrow subset of Earth’s available climates, characterized by mean annual temperatures around ∼13 °C. This distribution likely reflects a human temperature niche related to fundamental constraints. We demonstrate that depending on scenarios of population growth and warming, over the coming 50 y, 1 to 3 billion people are projected to be left outside the climate conditions that have served humanity well over the past 6,000 y. Absent climate mitigation or migration, a substantial part of humanity will be exposed to mean annual temperatures warmer than nearly anywhere today.

Significance

We show that for thousands of years, humans have concentrated in a surprisingly narrow subset of Earth’s available climates, characterized by mean annual temperatures around ∼13 °C. This distribution likely reflects a human temperature niche related to fundamental constraints. We demonstrate that depending on scenarios of population growth and warming, over the coming 50 y, 1 to 3 billion people are projected to be left outside the climate conditions that have served humanity well over the past 6,000 y. Absent climate mitigation or migration, a substantial part of humanity will be exposed to mean annual temperatures warmer than nearly anywhere today.

Global warming will affect ecosystems as well as human health, livelihoods, food security, water supply, and economic growth in many ways (12). The impacts are projected to increase steeply with the degree of warming. For instance, warming to 2 °C, compared with 1.5 °C, is estimated to increase the number of people exposed to climate-related risks and poverty by up to several hundred million by 2050. It remains difficult, however, to foresee the human impacts of the complex interplay of mechanisms driven by warming (13). Much of the impact on human well-being will depend on societal responses. There are often options for local adaptations that could ameliorate effects, given enough resources (4). At the same time, while some regions may face declining conditions for human thriving, conditions in other places will improve. Therefore, despite the formidable psychological, social, and political barriers to migration, a change in the geographical distribution of human populations and agricultural production is another likely part of the spontaneous or managed adaptive response of humanity to a changing climate (5). Clearly there is a need to understand the climatic conditions needed for human thriving. Despite a long and turbulent history of studies on the role of climate, and environment at large, on society in geography and beyond (6), causal links have remained difficult to establish, and deterministic claims largely refuted, given the complexities of the relationships in question (7). Rather than reentering the murky waters of environmental determinism (89), here we take a fresh look at this complex and contentious issue. We mine the massive sets of demographic, land use, and climate information that have become available in recent years to ask what the climatic conditions for human life have been across the past millennia, and then examine where those conditions are projected to occur in the future.

Current and Past Human Association to Climate

Our results reveal that today, humans, as well as the production of crops and livestock (Fig. 1 AD, and E), are concentrated in a strikingly narrow part of the total available climate space (Fig. 1G). This is especially true with respect to the mean annual temperature (MAT), where the main mode occurs around ∼11 °C to 15 °C (SI Appendix, Fig. S1). By contrast, much of range of precipitation available around that temperature (Fig. 1G and SI Appendix, Fig. S1) is used, except for the driest end. Soil fertility does not seem to be a major driver of human distribution (Fig. 1H), nor can potential productivity be a dominant factor, as net primary productivity shows a quite different geographical distribution (Fig. 1I), peaking in tropical rainforests, which have not been the main foci of human settlement.

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