October 11, 2023
New research has unveiled a dire forecast, indicating that over 2 billion people across India, Pakistan, and some of the world’s largest cities will face intolerable levels of heat within this century. The consequences will be particularly severe for megacities like Delhi, Shanghai, Lagos, and Chicago, where extreme heat will be most pronounced. This research highlights the potential for billions to struggle to survive during prolonged heatwaves as global temperatures continue to rise.
Impacts on Megacities
The study, conducted by the Penn State College of Health and Human Development, Purdue University College of Sciences, and Purdue Institute for a Sustainable Future, emphasizes that the most severe impacts will be felt by heavily populated regions, such as the US Midwest. These areas may experience prolonged periods of heatwaves that challenge the survival of their inhabitants.
Regions already grappling with heatwaves driven by the climate crisis, such as South Asia, will be at the forefront of the heatwave crisis. If global temperatures rise by 2 degrees Celsius or more compared to preindustrial levels, certain areas may be unable to naturally cool themselves.
The research found that if temperatures rise by 2 degrees Celsius above preindustrial levels, around 750 million people could face one week per year of potentially lethal humid heat. With a 3-degree increase, this threat would escalate to affect more than 1.5 billion people.
Global Warming Trajectory
Current policies are steering the world toward a 2.8-degree Celsius increase by the year 2100, as indicated in the 2022 UN Emissions Gap report. This trajectory overshoots the goal set by the Paris Agreement, signed by nearly 200 countries, which aims to limit global warming to 1.5 degrees Celsius.
Global Reach of the Heat Crisis
While India, Pakistan, and the Gulf region have already witnessed dangerous levels of humid heat, the study suggests that other major cities around the world will face similar challenges if global warming persists. The study’s lead author, Dr. Daniel Vecellio, points to emerging risks in South America and Australia.
The Wet-Bulb Temperature Measurement
Scientists rely on a measurement called “wet-bulb temperature” to track moist heat. This measurement is taken by covering a thermometer with a water-soaked cloth, replicating the process of sweat evaporation as the body’s cooling mechanism. The study builds on previous research, using wet-bulb temperature to determine the point at which heat and humidity become intolerable for the human body without shade or cooling technologies.
Limitations and Concerns
The study concluded that a wet-bulb temperature of 30-31 degrees Celsius is the critical limit beyond which people are likely to succumb to heat stress. This lower limit raises concerns about the growing threat of dangerous wet-bulb temperatures.
Another recent study, published last month in Science Advances, supported this threshold and highlighted the rapid expansion of regions prone to dangerous humid heat even with moderate global warming.