Earth’s surface temperature is on track to rise 2.7 degrees Celsius above preindustrial levels by 2100, which will push more than two billion people – 22 percent of projected global population – well outside the climate comfort zone that has allowed our species to thrive for millennia, scientists recently reported in Nature Sustainability.
The countries with the highest number of people facing deadly heat in this scenario are India (600 million), Nigeria (300 million), Indonesia (100 million), as well as the Philippines and Pakistan (80 million each).
“That’s a profound reshaping of the habitability of the surface of the planet, and could lead potentially to the large-scale reorganization of where people live,” said lead author Tim Lenton, director of Global Systems Institute at the University of Exeter.
According to the findings, successfully capping global warming to the 2015 Paris climate treaty target of 1.5C would sharply reduce the number of those at risk to less than half a billion, some five percent of the 9.5 billion people likely to inhabit the planet six or seven decades from now.
“The costs of global warming are often expressed in financial terms, but our study highlights the phenomenal human cost of failing to tackle the climate emergency,” said Lenton.
The threshold for “dangerous heat” used in the new findings is a mean annual temperature (MAT) of 29C.
Across history, human communities have been densest around two distinct MATs – 13C (in temperate zones) and to a lesser extent 27C (in more tropical climes). Global warming is pushing up the thermostat everywhere, but the risk of tipping into lethal heat is clearly higher in regions already close to the 29C red line.
Sustained temperatures at or beyond that level are strongly linked to greater mortality, reduced labor productivity and crop yields, along with more conflict and infectious disease.
Carbon cutting pledges by governments and companies have not yet translated in to action would stop the rise in global temperatures at, or even below, 2C, allowing hundreds of millions to avoid catastrophic heat. On the flip side scenarios even worse than the 2.7C world cannot be excluded either, the authors warn.
Among the countries singled out to be the most vulnerable to dangerous heat, the Philippines cannot continue to depend on the bigger and richer countries to bail it out, even if they do contribute more to climate change than we do. Our government and private sector need to act urgently as well, but before that, they will have make commitments and pledges in humanity’s long and arduous fight to keep the planet habitable for humans in the coming generations.*
