220 cr people in India, Pakistan at risk of intolerable heat waves: Study

Some 2.2 billion (220 crore) people living in the Indus River Valley region in northern India and eastern Pakistan may experience extended periods of heat that exceed human tolerance levels if global temperatures rise by 2 degrees Celsius above pre-industrial levels, new research says.

The research, published in the peer-reviewed journal Proceedings of the National Academy of Sciences (PNAS), shows that in such a scenario, northern India, eastern Pakistan, eastern China, and Sub-Saharan Africa would face high-humidity heatwaves.

Heatwaves with higher humidity levels can be more perilous because the air cannot efficiently absorb excess moisture. This restricts the human body's ability to evaporate sweat and affects the moisture content of certain infrastructure like evaporative coolers.

These regions are also home to lower- to middle-income countries, meaning that many affected individuals may lack access to air-conditioning or effective ways to mitigate the adverse health effects of extreme heat.

Human endurance

Humans can endure specific combinations of heat and humidity. However, when these thresholds are surpassed, individuals become susceptible to heat-related health issues, including heatstroke or heart attack.

With climate change driving global temperatures upward, billions could find themselves pushed beyond these limits, the research said.

The Earth's global surface temperature has already risen by 1.15 degrees Celsius. This is closely linked to the release of carbon dioxide (CO2), primarily by developed countries, into the atmosphere.

In 2015, 196 countries signed the Paris Agreement, aiming to limit the global temperature increase to 1.5 degrees Celsius above pre-industrial levels.

However, according to the Intergovernmental Panel on Climate Change (IPCC), an organisation composed of the world's leading climate scientists, the world is on course for a temperature increase of around 3 degrees Celsius by the end of this century under a business-as-usual scenario.

The IPCC emphasises that to avert extreme, destructive and likely irreversible effects of climate change, the world must cut emissions by half by 2030 compared to the 2019 levels. Only this will limit the rise in the global average temperature to 1.5 degrees Celsius relative to pre-industrial levels.

Searing hot

According to global agencies, the last four months (June, July, August and September) have been the hottest on record, with 2023 poised to become the warmest year ever.

The research team conducted modelling for global temperature increases ranging from 1.5 to 4 degrees Celsius, the latter considered a worst-case scenario where warming would accelerate.

This allowed them to identify areas where warming would lead to heat and humidity levels surpassing human tolerance.

In recorded human history, instances of temperatures and humidity exceeding human limits have been limited and occurred only briefly in the Middle East and Southeast Asia, according to the researchers.

If global warming continues to reach 3 degrees Celsius above pre-industrial levels, the researchers argue that areas such as the Eastern Seaboard and the middle of the US would begin to experience heat and humidity levels exceeding human tolerance.

Greenhouse emissions

South America and Australia would also face extreme heat at this level of warming.

To halt the rising temperatures, the researchers stress the need for significant reductions in greenhouse gas emissions, particularly carbon dioxide emissions from fossil fuel combustion.

Without these changes, middle-income and low-income countries are likely to be the hardest hit, the researchers warned.

(With agency inputs)