Global Warming Could Expose Two Billion People to Deadly Heat

James Cromwell recently shared a report that warns current policies to limit global warming could expose over a fifth of humanity to extreme and potentially life-threatening heat by the end of the century.

Earth's surface temperature is predicted to rise 2.7 degrees Celsius above preindustrial levels by 2100, pushing over two billion people out of their climate comfort zone. This would be 22% of the projected global population, which is a profound reshaping of the habitability of the planet's surface. The countries with the highest number of people facing deadly heat in this scenario are India, Nigeria, Indonesia, the Philippines, and Pakistan. "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 the Global Systems Institute at the University of Exeter. The study finds that capping global warming at the 2015 Paris climate treaty target of 1.5 degrees Celsius would sharply reduce the number of people at risk to less than half-a-billion, some 5% of the 9.5 billion people likely to inhabit the planet six or seven decades from now.

However, just under 1.2 degrees Celsius of warming to date has already caused devastating effects, such as intensifying heatwaves, droughts, and wildfires beyond what could have occurred absent the carbon pollution generated by burning fossil fuels and forests. "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. "For every 0.1 degree Celsius of warming above present levels, about 140 million more people will be exposed to dangerous heat." The threshold for "dangerous heat" used in the new findings is a mean annual temperature (MAT) of 29 degrees Celsius. Human communities have been densest around two distinct MATs throughout history: 13 degrees Celsius in temperate zones and, to a lesser extent, 27 degrees Celsius 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 29 degrees Celsius red line.

The study finds that the cost of global warming has a profound human cost. The poorest countries with the smallest per capita carbon footprints will be most impacted by extreme heat. Therefore, it is crucial global governments act now to prevent catastrophic heat and maintain a habitable environment for the planet.