Climate Claim: By 2070 Average Temperatures be “Unsuitable for Human Life to Flourish”

Guest essay by Eric Worrall

According to a new study, people don’t thrive in places where the average annual temperature is higher than 15C / 59F.

Unsuitable for ‘human life to flourish’: Up to 3B will live in extreme heat by 2070, study warns

Doyle Rice USA TODAY
May 4, 2020

By 2070, up to 3 billion people are likely to live in climate conditions ‘deemed unsuitable for human life to flourish.’

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If global warming continues unchecked, the heat that’s coming later this century in some parts of the world will bring “nearly unlivable” conditions for up to 3 billion people, a study released Monday said. 

The authors predict that by 2070,  much of the world’s population is likely to live in climate conditions that are “warmer than conditions deemed suitable for human life to flourish.”

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That “niche” is equivalent to average yearly temperatures of roughly 52 to 59 Fahrenheit. The researchers found that people, despite all forms of innovations and migrations, have mostly lived in these climate conditions for several thousand years. 

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“Large areas of the planet would heat to barely survivable levels and they wouldn’t cool down again,” said study co-author Marten Scheffer of Wageningen University in the Netherlands. “Not only would this have devastating direct effects, it leaves societies less able to cope with future crises like new pandemics. The only thing that can stop this happening is a rapid cut in carbon emissions.”

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Read more: https://www.usatoday.com/story/news/world/2020/05/04/world-heat-conditions-unlivable-global-warming-unabated/3063849001/

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
PNAS first published May 4, 2020 https://doi.org/10.1073/pnas.1910114117

Contributed by Marten Scheffer, October 27, 2019 (sent for review June 12, 2019; reviewed by Victor Galaz and Luke Kemp)

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/early/2020/04/28/1910114117

The explanation the study authors give for why they don’t think humans thrive above 59F;

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.

Read more: Same link as above

My view, this kind of study is what happens when a bunch of scientists based in temperate climates didn’t enjoy their last Caribbean holiday.

There is substantial evidence the “optimum” described in the study is a historical accident. There are plenty of cultures like Thailand and India, which built large populous nations with big cities, even conquered empires, without the “benefits” of a temperate climate, not to mention wealthy modern day tropical nations like Singapore, Malaysia and increasingly Indonesia.