More than 200 crore people worldwide, including over 60 crore in India, would be exposed to dangerously hot temperatures even if all countries meet their promised emission cuts, a new research says.
The study has also found that the lifetime emissions of 3.5 average global citizens today -- or just 1.2 US citizens -- expose one future person to dangerous heat, highlighting the inequity of the climate crisis as these future heat-exposed people will live in places where emissions today are around a half of the global average.
In "worst-case scenarios" of 4.4-degrees Celsius global warming, 50 per cent of the world's population could be exposed to unprecedented hot temperatures, posing what the researchers call an "existential risk".
According to climate scientists, current climate policies will result in 2.7-degrees Celsius warming by the end of the century (2080-2100), a rise that is likely to increase the frequency of extreme weather events, such as deadly heatwaves, cyclones and floods, and sea-level rise globally.
The researchers at the Global Systems Institute, University of Exeter, associated with the Earth Commission, and Nanjing University assessed what 2.7-degrees Celsius warming would mean for those living outside the "climate niche", defined as the historically highly conserved distribution of relative human population density with respect to the mean annual temperature.
"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 Professor Tim Lenton, director of the Global Systems Institute at the University of Exeter.
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The researchers said 22 per cent to 39 per cent of the projected end-of-century population (950 crore) would be exposed to dangerous heat (average temperature of 29 degrees Celsius or higher).
Reducing global warming from 2.7 degrees Celsius to 1.5 degrees Celsius would result in a five-fold decrease (from 22 per cent to 5 per cent) in the population exposed (from 210 crore to 40 crore) to unprecedented heat, they said.
More than 60 crore people (about 9 per cent of the global population) are already exposed to dangerous heat, the study says.
At 2.7-degrees Celsius global warming, India would have the greatest population exposed -- more than 60 crore. At 1.5 degrees Celsius, this figure would be far lower, at about nine crore.
Nigeria would have the second-largest heat-exposed population at 2.7-degrees Celsius global warming -- more than 30 crore. At 1.5-degrees Celsius warming, this would be less than four crore.
At 2.7-degrees Celsius, almost 100 per cent of certain countries, including Burkina Faso and Mali, will be dangerously hot for humans. Australia and India would also experience massive increases in the area exposed (around 40 per cent).
Under the Paris Agreement, more than 190 countries had pledged to limit the increase in global temperatures to well below 2 degrees Celsius (compared to pre-industrial levels) and preferably, to 1.5 degrees Celsius.
Scientists consider 1.5 degrees Celsius of warming as a tipping point, beyond which the chances of extreme heatwaves, flooding, drought and wildfires could increase dramatically.
The earth's global surface temperature has risen by around 1.15 degrees Celsius as compared to the pre-industrial (1850-1900) average and the greenhouse gases spewed into the atmosphere since the start of the industrial revolution is closely tied to it.
The World Meteorological Organisation (WMO) has said the planet is now likely to breach the 1.5-degrees threshold, though temporarily, for the first time within the next five years. It is a clear signal how quickly human-caused climate change is accelerating as countries put record levels of GHG emissions into the atmosphere.
The WMO also said at least one of the next five years is almost certain to become the warmest on record.
Top climate scientists say the world as a whole must reach net zero carbon emissions by 2050 to limit the global temperature rise to 1.5 degrees Celsius.
Ashish Ghadiali of Exeter's Global Systems Institute said: "These new findings from the leading edge of earth systems science underline the profoundly racialised nature of projected climate impacts and should inspire a policy sea-change in thinking around the urgency of decarbonisation efforts as well as in the value of massively up-shifting global investment into the frontlines of climate vulnerability." Wendy Broadgate, executive director of the Earth Commission at Future Earth, said: "We are already seeing effects of dangerous heat levels on people in different parts of the world today. This will only accelerate unless we take immediate and decisive action to reduce greenhouse gas emissions."