Combined haze and heat to pummel Southeast Asia more often

A new report shows how often people in Southeast Asia will simultaneously face air pollution and heat hazards.

Scientists know that extreme heat has a negative impact on the human body—causing distress in the respiratory and cardiovascular system and they know that extreme air pollution can also have serious effects.

But as climate change impacts continue globally, how often will people face both extremes at once? The regional research study in the journal AGU Advances answers that question for South Asia.

“South Asia is a hotspot for future climate change impacts,” says Yangyang Xu, an assistant professor in the department of atmospheric sciences in the College of Geosciences at Texas A&M University. Extreme heat occurrences worldwide have increased in recent decades, and at the same time, many cities are facing severe air pollution problems, featuring episodes of high particulate matter (PM) pollution, he says. The new study provides an integrated assessment of human exposure to rare days of both extreme heat and high PM levels.

“Our assessment projects that occurrences of heat extremes will increase in frequency by 75% by 2050, that is an increase from 45 days a year to 78 days in a year. More concerning is the rare joint events of both extreme heat and extreme PM will increase in frequency by 175% by 2050,” Xu says.

Climate change is not just a global average number—it is something you can feel in your neighborhood, he says, and that’s why regional-scale climate studies are important.

The study’s regional focus was South Asia: Afghanistan, Bangladesh, Bhutan, India, Myanmar, Nepal, and Pakistan. The scientists used a high-resolution, decadal-long model simulation, using a state-of-the-science regional chemistry-climate model.

Xu led the first-of-its-kind research project, and scientists from the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, led the development of the fully coupled chemistry-climate model and performed model simulations for the present-day and future conditions.

“These models allow chemistry and climate to affect each other at every time step,” says Rajesh Kumar, a project scientist at NCAR and coauthor of the study.

As climate change impacts continue to become reality, it is important for scientists to consider human impacts of multiple extreme conditions happening simultaneously, says Xu.

Projected increases in humidity and temperature are expected to cause extreme heat stress for the people of South Asia, where the population is projected to increase from 1.5 billion people to 2 billion by 2050.

“It is important to extend this analysis on the co-variability of heat and haze extremes in other regions of the world, such as the industrial regions of the US, Europe, and East Asia,” says coauthor Mary Barth, a senior scientist at NCAR and coauthor of the study.

The analysis also shows that the fraction of land exposed to prolonged dual-extreme days increases by more than tenfold in 2050.

“I think this study raises a lot of important concerns, and much more research is needed over other parts of the world on these compounded extremes, the risks they pose, and their potential human health effects,” says Xu.

NCAR has funding from the National Science Foundation and is managed by the University Corporation for Atmospheric Research.

Source: Texas A&M University

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