The researchers say that heat stress will probably increase the health risks of millions of people by the end of the 21st century and show an additional reason to achieve important climate and emissions objectives. An article in the Earth’s future published on April 26 draws on many variables of heat stress, where other studies tend to focus only on one aspect, such as duration or temperature. The scientist found that the potential impact of heat-stress events lasting between one day and one week will double between 2060-1999 in the United States, with a significant increase in the population on both the eastern and west coasts.
“The heat stress events in the past are probably more common in the future,” said Clemson University co-author Ashok Mishra, a professor of Civil Engineering. “Overall, in the future, we shall probably see more extremes.”
Heat stress is a significant cause of worldwide death, with communities with low incomes bearing a considerable burden. National Wetter Service defines the “feel like” measurement that combines temperature and humidity as excessive heat exposure. Excessive heat exposure or heat stress is equal to a heat index of more than 105 degrees Fahrenheit for the agency.
According to the Environmental Protection Agency, a “stressful” heat index can not only induce heat exhaustion and heat strokes but may also exacerbate heart disease and may lead to heart attacks and strokes. Individuals 65 and older also are more sensitive to heat stress hazards. After record-breaking heat waves in the Southeast USA in the summers of 2019 and 2020, Mishra and lead author Sourav Mukherjee, a Ph.D. student in water resources engineering in Clemson, began examining heat stress. The pair and colleagues collect the first data on the climate, the temperature and humidity from 1980 to 2019, and heat stress is calculated from this period to determine the potential impact of thermal stress.
Then, using projected climate and population information, they projected these values for the near and far future and developed a framework to examine the current and projected potential effects of heat stress. Notably, the humidity calculations promote heat stress. “If we only take the temperature into account, it’s all right, but if you include the moisture that’s being done in this study, that will have a significant health impact as it’s not that the body’s humidity cools out,” Mishra told.
The increasing population on the eastern and western coasts of the United States is projected to cause heat stress as urban populations grow and rural populations deteriorate. Heat stress will be even more dangerous because, according to Mishra, since the 1960s, temperatures have not gone up linearly. More variability is increasing, making them more challenging to adapt to. These fluctuating, fast changes in the heat stress are also accounted for, which previous studies have not accomplished.
‘Suppose I’m at a temperature of 70 degrees Fahrenheit, and suddenly there’s a hundred degree Fahrenheit heatwave for the next couple of days,’ said Mukherjee. “It is also a hot shock to the body, and to this shock, the body must be acknowledged.” A recent study in Tobacco hornworm larvae has confirmed that heat stress has had some adverse effects because larvae that have been subjected to long waves of heat have not grown or have not had any heat waves.
The take-off is, according to Mukherjee, “how to understand the consequences of geographical region indication that may have an aggressive potential impact during aggressive scenarios of emission without mitigation.” According to Mishra, the efficient reduction of greenhouse gas emissions contributing to climate change could result from net-zero carbon initiatives aiming to reduce and ultimately eliminate it drastically.
The U.S. and Canadian governments jointly announced a new initiative to make public infrastructure and activities free from emissions by 2050. “To prevent the 1,5 Celsius warmth limit from crossing,” said co-author Michael Man, distinguished professor of the atmospherics of Pennsylvania State University, “We need to reduce carbon emissions globally by a factor of two over the next decade. “Biden has committed the U.S. to live up to this commitment, but now has to work together with Congress to advance a specific policy agenda that includes measures such as carbon pricing and renewable energy subsidies that can fulfil this commitment.”
According to Mann, the threshold of 1,5 degrees Celsius is vital since it is the time of exceeding heat stress and other harmful climate effects to increase “significantly.” The more aspiring objective of the international Paris Agreement is to limit the global temperature increase by that amount.
Mishra and Mukherjee are keen to expand their research on heat stress to examine what factors can contribute to heat stress aside from temperature and humidity. This could include soil moisture because soil with low moisture absorbs less heat than soil with high humidity. According to Mishra, it contributes to a higher temperature of the lower atmosphere.
The duo also believes that the study opens new ways to look at where heat stress occurs and who it most hurts. For example, in low-income communities, access to air conditioning is less common. Mishra and Mukherjee intend to study the differences between heat stress and populations in future and possibly work with social scientists.

Journal Reference:

Mukherjee, S., Mishra, A. K., Mann, M. E., & Raymond, C. (2021). Anthropogenic warming and population growth may double US heat stress by the late 21st century. Earth’s Future, 9, e2020EF001886.

Main image credit: CIMMYT