'Dangerous heat' set to affect billions by 2100: Study

Researchers warned on Monday (May 22) that more than a fifth of the human population will face extreme and probably life-threatening heat by 2100 if current policies to limit global warming continue. The report was published in the journal Nature Sustainability, reported AFP.

According to the report, the countries with the most people at risk are India (600 million), Nigeria (300 million), Indonesia (100 million), 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 reorganisation of where people live," said lead author Tim Lenton, director of the Global Systems Institute at the University of Exeter.

The findings underlined the immediate need to take steps in order to cap global warming at 1.5C. It said that doing so would sharply reduce the number of those at risk. The number would fall to half a billion. This will be around five per cent of the projected 9.5 billion global population.

Just under 1.2C of warming, to date, has already amplified the intensity or duration of heatwaves, droughts and wildfires beyond what could have occurred minus the carbon pollution generated by burning fossil fuels and forests. The last eight years were the hottest on record.

"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 0.1C of warming above present levels, about 140 million more people will be exposed to dangerous heat."

The threshold for 'dangerous heat'

The new findings have found the threshold for 'dangerous heat'. The report says that it is at a mean annual temperature (MAT) of 29C.

Historically, human settlements have been densest around two MATs. 13C when it comes to temperate zones and 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.

Studies have reportedly shown that sustained high temperatures at or beyond this threshold have strong links to greater mortality, and reduced productivity of labour and crop yields. This also increases the likelihood of more conflict and infectious diseases.

As recently as 40 years ago, only 12 million people worldwide were exposed to such extremes. 

That number has today increased five-fold, and will climb ever more steeply in the coming decades, the study found.