As to 'sweat', quite literally: a study published last week in PNAS, which has only now begun to be picked up by the press found that in less than 100 years, parts of the planet could become so hot and humid that humans would die of heat stress 'even if they were naked in the shade, soaking wet and standing in front of a large fan," Steven Sherwood, (University of New South Wales, Sydney), lead author of the study, told USA Today.
On the whole humans can survive, even live, in temperatures of 45 °C or more, so long as humidity is low enough to allow them to keep their skin cool by sweating. In a very hot and humid environment, sweating slows down and skin temperature rises. If it exceeds 35 °C, most humans will probably die in a matter of hours.
In technical terms, this is called the wet-bulb temperature; i.e. the temperature recorded by a thermometer covered in a wet cloth and kept well ventilated. For now, according to the New Scientist, nowhere on Earth has a wet-bulb temperature of more than 30 °C. But a global temperature rise of 11 °C would mean that vast areas, including much of the eastern US, the entire Indian subcontinent, most of Australia and parts of China, would have wet-bulb temperatures of more than 35 °C for at least part of the year.
Projected regional wet-bulb temperatures for an average global temperature increase of 12 C. Humans cannot survive wet-bulb temperatures over 35 C (Image: Steven C. Sherwood/Matthew Huberb. Image source: New Scientist)
According to current predictions, global temperature is set to rise by 4 °C to 7 °C by 2100 (see The Copenhagen Diagnosis 2009).
It takes little more than common sense to see that the consequences on species diversity and migration are likely to be disastrous. If vast regions become virtually uninhabitable, entire populations will seek to relocate to the ever-shrinking inhabitable areas. Of course, environmental migrants, environmental refugees, or 'climigrants' are nothing new: extreme environmental events, such as earthquakes and storms, as well as environmental deterioration because of human mismanagement often cause the displacement of large numbers of people. In those cases, however, once the environment has had a chance to recuperate it is usually possible for people to return. On the contrary, with climate change and rises in temperature that may take decades to restore to acceptable levels, reverse migration will not be possible – unless the claustrophobic cities of sci fi scenarios become reality.
In fact, although graphic violence and images of suffering caused by war may have a greater appeal to the media, because of their power to attract viewers, environmental change is a much more powerful, though less sensational, displacer than war: in 2008, 20 million persons were displaced by extreme weather events, compared to 4.6 million internally displaced by conflict and violence, according to the International Organization for Migration's figures. Gradual environmental changes have an even greater impact on migration than extreme events: between roughly 1980 and 2008, twice as many people were affected by droughts as by storms (1.6 billion compared with approximately 718 million).
By 2050, anything from a conservative 25 million to a staggering 1 billion of environmental migrants are expected to move either within their countries or across borders, with 200 million being the most widely cited estimate.
It takes little more than common sense to see that the consequences on species diversity and migration are likely to be disastrous. If vast regions become virtually uninhabitable, entire populations will seek to relocate to the ever-shrinking inhabitable areas. Of course, environmental migrants, environmental refugees, or 'climigrants' are nothing new: extreme environmental events, such as earthquakes and storms, as well as environmental deterioration because of human mismanagement often cause the displacement of large numbers of people. In those cases, however, once the environment has had a chance to recuperate it is usually possible for people to return. On the contrary, with climate change and rises in temperature that may take decades to restore to acceptable levels, reverse migration will not be possible – unless the claustrophobic cities of sci fi scenarios become reality.
In fact, although graphic violence and images of suffering caused by war may have a greater appeal to the media, because of their power to attract viewers, environmental change is a much more powerful, though less sensational, displacer than war: in 2008, 20 million persons were displaced by extreme weather events, compared to 4.6 million internally displaced by conflict and violence, according to the International Organization for Migration's figures. Gradual environmental changes have an even greater impact on migration than extreme events: between roughly 1980 and 2008, twice as many people were affected by droughts as by storms (1.6 billion compared with approximately 718 million).
By 2050, anything from a conservative 25 million to a staggering 1 billion of environmental migrants are expected to move either within their countries or across borders, with 200 million being the most widely cited estimate.
As the International Organization for Migration report points out, 'the relationship between environmental and climate change and migration is often complicated by the multifaceted associations with other factors, such as population growth, poverty, governance human security and conflict.' The impact of mass migration, regardless of its causes, on both the countries the migrants flee and the countries they flock to is enormous, highly complex, and potentially devastating, for social, economic, political, as well as environmental stability. That's where the blood and tears come in.
Image from the German Advisory Council on Global Change (WBGU, 2007)
(Sources: the New Scientist, the Copenhagen Diagnosis, the International Organization for Migration, the German Advisory Council on Global Change)
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