06 May 2010

An Earth Too Hot For Humans?

In worst-case but possible warming scenarios, much of Earth could become too hot for human habitation. That's the gist of recent research by Steven C. Sherwood of the Climate Change Research Centre, University of New South Wales and Matthew Huber of the Purdue Climate Change Research Center published in PNAS (Abstract here, article behind pay wall).

This graphic shows areas that could be too hot for humans in one scenario (12 degrees C over pre-industrial levels, I think). The too-hot areas include much of Africa, the American Southeast, Australia, Brazil India, Oceana and eastern China.

From their 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 wet-bulb temperature TW, is surprisingly similar across diverse climates today. TW 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.
Translation (mostly from Purdue press release):
The researchers calculated the highest tolerable "wet-bulb" temperature and found that this temperature could be exceeded for the first time in human history in future climate scenarios if greenhouse gas emissions continue unabated.

"Although areas of the world regularly see temperatures above 100 degrees, really high wet-bulb temperatures are rare," co-author Huber said. "This is because the hottest areas normally have low humidity, like the 'dry heat' referred to in Arizona. When it is dry, we are able to cool our bodies through perspiration and can remain fairly comfortable. The highest wet-bulb temperatures ever recorded were in places like Saudi Arabia near the coast where winds occasionally bring extremely hot, humid ocean air over hot land leading to unbearably stifling conditions, which fortunately are short-lived today."

The challenges presented by the future climate scenarios are daunting in their scale and severity, he said.

"Whole countries would intermittently be subject to severe heat stress requiring large-scale adaptation efforts," Huber said. "One can imagine that such efforts, for example the wider adoption of air conditioning, would cause the power requirements to soar, and the affordability of such approaches is in question for much of the Third World that would bear the brunt of these impacts. In addition, the livestock on which we rely would still be exposed, and it would make any form of outside work hazardous."

"We found that a warming of 12 degrees Fahrenheit would cause some areas of the world to surpass the wet-bulb temperature limit, and a 21-degree warming would put half of the world's population in an uninhabitable environment," Huber said. "When it comes to evaluating the risk of carbon emissions, such worst-case scenarios need to be taken into account."

"The wet-bulb limit is basically the point at which one would overheat even if they were naked in the shade, soaking wet and standing in front of a large fan," lead author Sherwood said. "Although we are very unlikely to reach such temperatures this century, they could happen in the next."
On the other hand, the 22nd century is a long time from now. Who knows what technology will be available to keep people and livestock comfortable even in lethal environments. But it could be a very different Earth.

[Update 2013-02-25 1800GMT:
Recent research by NOAA scientists suggests warming is already reducing capacity of people to work in many regions, and could have severe effects by 2050. "This planet will start experiencing heat stress that's unlike anything experienced today," says one of the authors of the study in Nature Climate Change. (Abstract here; article behind Nature paywall.) Here is a Reuters item about the research.]

1 comment:

  1. Your finding of severe stress in work really makes it urgent to demand 100 percent reduction in greenhouse emissions immediately in the key culprits for global warming and environmental problems: Australia and Southern Africa. Those people or communities affected in their working capacity have every right to sue Australia’s polluting coal and mineral corporations - and its pro-freeway politicians - and demand that they pay to give Australia a rigidly mandated goal of one hundred percent renewable energy and a constitutionally demanded one hundred percent of private and government transport investment in railways. Coal mining would need to be stopped and private cars absolutely banned from Australia.

    Owing to their extremely infertile soils and long growing seasons, these regions have extremely low primary productivity but do not lose carbon to respiration as the much younger and more fertile soils of the northern and western hemispheres do.

    In addition, Australia and Southern Africa, without tectonic uplift to produce land too steep to farm, have a large comparative advantage in food production over much more sustainable lands in cooler climates. They also have not lost to glaciation or mountain building reserves of essential industrial minerals such as iron ore, bauxite, manganese and titanium that are inexhaustible on their weathered soils. They are also very rich in coal.

    The result is that these countries are under negligible economic or political pressure to produce a more sustainable energy system, and their greenhouse emissions are among the highest in the world especially relative to income.

    In ecological terms, the allowable per capita greenhouse emissions of Australia and Southern Africa are orders of magnitude lower than in the northern and western hemispheres. This is because of the extremely low energy consumption of native animals in Australia and Southern Africa due to scanty food supply - especially of animal foods - and the effect of global warming on the exceptional biological diversity of these regions.

    In order to do this, Europe, North America and East Asia need to realise they have a common interest in fighting polluting Australia and South Africa with the tropical nations. They will need to redirect money spent on improving their own energy efficiency to demanding zero emissions in Australia and Southern Africa - and being willing to punish them with at the very least loss of essential fertiliser minerals if they cannot meet these severe targets faultlessly.


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