The temperature is on track to rise 2.7 degrees Celsius above preindustrial levels by 2100, pushing more than two billion people (22 percent) well outside the climate comfort zone, said scientists in Nature Sustainability.
The scientists mention that India (600 million), Nigeria (300 million), Indonesia (100 million), Philippines and Pakistan (80 million each) wold face highest number of people facing deadly heat.
“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.
CAPPING GLOBAL TEMPERATURE
The scientists believe that capping global warming at the 2015 Paris climate treaty target of 1.5 °C would sharply reduce the number of those at risk to less than half-a-billion. Just under 1.2 °C of warming to date has already amplified the intensity or duration of heat waves, droughts, and wildfires beyond what could have occurred absent the carbon pollution generated by burning fossil fuels and forests.
Lenton said that though the costs of global warming are often expressed in financial terms, their study highlighted the phenomenal human cost of failing to tackle the climate emergency. “For every 0.1 °C 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 °C.
Across history, human communities have been densest around two distinct MATs – 13 °C (in temperate zones) and to a lesser extent 27 °C (in more tropical climes), said the scientists.
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 °C red line.
They said that only 12 million people worldwide were exposed to such extremes 40 years ago. The numbers have increased five-fold, and will climb ever more steeply in coming decades.
The risk is accentuated in regions straddling the equator, where human populations are expanding most rapidly: tropical climes can become deadly even at lower temperatures when high humidity prevents the body from cooling itself through sweating.
The study showed that most exposed to extreme heat live mostly in poorer countries with the smallest per capita carbon footprints. According to the World Bank, India emits on average about two tonnes of CO2 per person every year. Nigerians emit about half-a-tonne annually, compared to less than seven tonnes per person in the European Union and 15 in the United States.
They maintained that carbon-cutting pledges by governments and companies not yet translated into action would stop the rise in global temperatures at – or even below – 2 °C, allowing hundreds of millions to avoid catastrophic heat.
If past and continuing emissions trigger the release of natural carbon stores, such as in permafrost, or warm the atmosphere more than anticipated, temperatures could climb nearly four degrees above mid-19th century levels, they said.
WHAT ARE THE EFFECTS OF EXTREME HEAT ON HUMAN HEALTH?
Heat-related illnesses: These include heat cramps, , heatstroke, heat exhaustion and hyperthermia. They occur when the body’s ability to regulate temperature is overwhelmed by excessive heat. They can cause symptoms such as muscle spasms, nausea, headache, confusion, dizziness, fainting, seizures, coma, and death.
Cardiovascular and respiratory disorders: Exposure to high temperatures can increase the risk of heart attacks, strokes, and respiratory diseases. This is because heat can cause dehydration, blood vessel dilation, increased heart rate and blood pressure, reduced blood flow to vital organs, inflammation, and oxidative stress.
Mental health problems: Extreme heat can affect mental health by disrupting sleep quality, impairing cognitive performance, and increasing the risk of suicide or hospital admission for mental illness. Heat can also trigger or worsen existing mental health conditions such as depression, anxiety, bipolar disorder, and schizophrenia.
Indirect effects: Extreme heat can also have indirect effects on human health by affecting food security, water quality, air quality, infectious diseases, social conflicts, and economic productivity.