Guest essay by Eric Worrall

Despite humans being tropical apes, we apparently find it very difficult to survive outside of temperate zones where average annual temperature ranges from 52F – 59F (11C-15C).

Climate change could bring near-unliveable conditions for 3bn people, say scientists

Each degree of warming above present levels corresponds to roughly 1bn people falling outside of ‘climate niche’

Steven Bernard, Dan Clark and Sam Joiner

Up to 3bn out of the projected world population of about 9bn could be exposed to temperatures on a par with the hottest parts of the Sahara by 2070, according to research by scientists from China, US and Europe.

However, rapid reductions in greenhouse gas emissions could halve the number of people exposed to such hot conditions. “The good news is that these impacts can be greatly reduced if humanity succeeds in curbing global warming,” said study co-author Tim Lenton, climate specialist and director of the Global Systems Institute at Exeter university.

The report highlights how the majority of humans live in a very narrow mean annual temperature band of 11C-15C (52F-59F). Researchers noted that despite all innovations and migrations, people had mostly lived in these climate conditions for several thousand years.

“This strikingly constant climate niche likely represents fundamental constraints on what humans need to survive and thrive,” said Professor Marten Scheffer of Wageningen University, who co-ordinated the research with his Chinese colleague Chi Xu, of Nanjing University.

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Read more: https://www.ft.com/content/072b5c87-7330-459b-a947-be6767a1099d

The abstract of the study;

Future of the human climate niche

 Chi Xu, Timothy A. Kohler, Timothy M. Lenton, Jens-Christian Svenning, and Marten Scheffer

All species have an environmental niche, and despite technological advances, humans are unlikely to be an exception. Here, we demonstrate that for millennia, human populations have resided in the same narrow part of the climatic envelope available on the globe, characterized by a major mode around ∼11 °C to 15 °C mean annual temperature (MAT). Supporting the fundamental nature of this temperature niche, current production of crops and livestock is largely limited to the same conditions, and the same optimum has been found for agricultural and nonagricultural economic output of countries through analyses of year-to-year variation. We show that in a business-as-usual climate change scenario, the geographical position of this temperature niche is projected to shift more over the coming 50 y than it has moved since 6000 BP. Populations will not simply track the shifting climate, as adaptation in situ may address some of the challenges, and many other factors affect decisions to migrate. Nevertheless, in the absence of migration, one third of the global population is projected to experience a MAT >29 °C currently found in only 0.8% of the Earth’s land surface, mostly concentrated in the Sahara. As the potentially most affected regions are among the poorest in the world, where adaptive capacity is low, enhancing human development in those areas should be a priority alongside climate mitigation.

Read more: https://www.pnas.org/content/117/21/11350

My home in Queensland, Australia, experiences an average annual temperature of around 77F (25C), 18F above the alleged human climate niche.

Last time I checked our state enjoyed a prosperous agriculture and mining economy, with vibrant cities full of happy people who mostly don’t own heavy overcoats.

The far North of Australia which includes some of our most prosperous agricultural and mining regions, are even hotter.

Then you have nations like Singapore, Indonesia, Kenya, and Colombia, all established or up and coming economic success stories which sit right on the equator. Venezuela used to be successful, but their problems have nothing to do with global warming.

These glaring exceptions to the “human environmental niche” should be considered strong evidence that prosperity is possible outside the 52F – 59F zone where the bulk of people live. But the authors dismiss this, arguing there is a ongoing causal element to human distribution.

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The Question of Causality.

Why have humans remained concentrated so consistently in the same small part of the potential climate space? The full complex of mechanisms responsible for the patterns is obviously hard to unravel. The constancy of the core distribution of humans over millennia in the face of accumulating innovations is suggestive of a fundamental link to temperature. However, one could argue that the realized niche may merely reflect the ancient needs of agrarian production. Perhaps, people stayed and populations kept expanding in those places, even if the corresponding climate conditions had become irrelevant? Three lines of evidence suggest that this is unlikely, and that instead human thriving remains largely constrained to the observed realized temperature niche for causal reasons.

First, an estimated 50% of the global population depends on smallholder farming (19), and much of the energy input in such systems comes from physical work carried out by farmers, which can be strongly affected by extreme temperatures (20). Second, high temperatures have strong impacts (21⇓–23), affecting not only physical labor capacity but also mood, behavior, and mental health through heat exhaustion and effects on cognitive and psychological performance (20, 24, 25). The third, and perhaps most striking, indication for causality behind the temperature optimum we find is that it coincides with the optimum for economic productivity found in a study of climate-related dynamics in 166 countries (12). To eliminate confounding effects of historical, cultural, and political differences, that study focused on the relation within countries between year-to-year differences in economic productivity and temperature anomalies. The ∼13 °C optimum in MAT they find holds globally across agricultural and nonagricultural activity in rich and poor countries. Thus, based on an entirely different set of data, that economic study independently points to the same temperature optimum we infer.

Altogether, it seems plausible that the historically stable association between human distribution and temperature reflects a causal link rather than a legacy, contingent on ancient patterns reflecting agrarian needs or still-more-ancient hunter-gatherer preferences. This supports the view that the historically stable and tight relationship of human distribution to MAT represents a human temperature niche reflecting fundamental constraints on human populations.

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Read more: https://www.pnas.org/content/117/21/11350

I mean I guess its possible all this mild weather is bad for my health. Perhaps all the comfortable year round temperatures and our harsh diet of BBQ meat, fresh salad, beer, beach parties and outdoor living all year round will eventually finish us. But in my opinion the authors need to present stronger evidence than a demographic map, and a failure to address exceptions to their environmental niche hypothesis.

Update (EW): Added the full study discussion on “Causality”.

via Watts Up With That?

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November 2, 2021