Without a significant action to prevent the growth of levels of greenhouse gas emissions, the world could potentially suffer from increasing temperatures and humidity, exposing hundreds of millions of people to lethal heat stress by 2060, a new study warns. Tropical regions of India, Southeast Asia, the Middle East, and Africa are at high risk of experiencing the impact of global warming.

The study, recently presented at the American Geophysical Union meeting, is the first to analyse the future impact of heat stress on a global basis, researchers said. The findings come from the analysis of climate models and population projections, showing how many people could suffer from dangerous heat in 2060.

For the study, researchers assumed greenhouse gas emissions would continue to increase sharply on a “business-as-usual” course. They used the forecasts of “wet bulb” temperatures, a technique that measures the temperature of a moist surface cooled by evaporation.

The human body has the normal temperature of 37°C and the skin typically reaches 35°C. As the temperature of the air measured by the wet bulb exceeds that level, it would be impossible for the body to tolerate the heat, which a fit individual could potentially die within six hours, the National Geographic reports.

To date, the wet bulb temperature does not increase above 31°C even in hottest spots on Earth. However, a study in October predicts that by 2100, Persian Gulf cities, such as Abu Dhabi or Dubai, could experience heat higher than the 35°C threshold of human survival.

The researchers of the current study said that by the 2060s, about 250 million people could experience 33°C at least once a year, and around 700 million people could be exposed to 32°C. These conditions could be dangerous for some people.

Oceans could also contribute to the dangerous increase in temperature. Rising temperatures add more moisture in the atmosphere, particularly around warming oceans, which could lead extreme heat and humidity to become more common and intense in many parts of the world.

Researchers said cities like New York and London could potentially experience temperatures that are near the limits of what people there can tolerate. “Local ocean temperatures can be a really big driver for the extent of these high heat and humidity events,” study co-author Radley Horton told the National Geographic.

The lethal heat stress events across the world could possibly prompt more people to use air conditioning, Horton said. However, with the convenience of using air conditioners comes the impact of using more electricity and fossil fuels to generate energy to the environment.

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