Extremely hot days and extreme air pollution are increasing around the world. Last November, New Delhi experienced a week of the worst air pollution in human history. The entire city closed and the planes couldn't see well enough to land. Not long before that, Western Europe crashed with two record heat waves that killed nearly 1,500 people.
Extreme hot days and extreme pollution often don't overlap, but our two teams at Texas A&M wanted to see if the number of these double extreme days was increasing and explore what the health risks might be.
To test this, we used a computer model to observe the concurrence of extreme heat and extreme air pollution in South Asia. The model incorporated trends in greenhouse gas emissions and air pollution from industrial and residential sources, population growth, migration trends, and even how air pollution is affected by climate, terrain, and the nearby oceans.
We predict that the frequency of days with extreme heat and pollution, and the number of people who will be affected by those days, could greatly increase by 2050.
We focus on South Asia because it is already a point of climate change and its population is projected to increase from 1.5 billion today to 2 billion in 2050. Under the worst climate change scenario and with little reduction in CO2 and other pollutants, days with extreme heat and extreme pollution would increase in frequency by 175% in the region, resulting in approximately 78 days a year with those double-whammy conditions.
Furthermore, the amount of land that would experience this dual threat for 60 days or more per year would increase tenfold between 2000 and 2050, from 2% to more than 25% of all of South Asia. This will also lead to more than 52% of the population being exposed to more than 60 days of this double danger.
Because it is important
Both extreme heat and air pollution have serious negative effects on the human body. Extreme heat increases the likelihood of heat exhaustion and heat stroke, but it can also make chronic ailments like heart disease worse. As part of an effort to better understand how extreme heat affects death rates, we are currently studying the health effects of extreme heat here in Texas.
Air pollution is known to cause asthma, heart disease, pregnancy complications, and other serious health effects.
So what happens when a person experiences both at the same time? Scientists know that when a person experiences air pollution in addition to another concurrent stressor, they become more susceptible to both. This has been shown for combinations such as air pollution and smoking, as well as air pollution and COVID-19.
It is difficult to say exactly what effect prolonged exposure to the dual threats of heat and air pollution would have on human health, as there have only been a few case studies looking at the combined effects of both. The results, though scant, suggest that more people die when both conditions occur.
What is not yet known
The health effects of a combination of extreme heat and extreme pollution are largely unknown, especially in many developing countries where studies have not been conducted and the extremes are expected to become more severe. Billions of people are expected to experience these conditions in the coming decades, but researchers know little about what the risks are.
Which populations, both demographically and in terms of chronic diseases, are most at risk? How dangerous are these double extreme days for human health? Where are the populations most at risk?