Extreme heat and pollution are bad in themselves. Together, they’re even deadlier: ScienceAlert

On the morning news, you see the weather forecast calling for high heat and there is an “excessive heat watch” for later in the week.

You hoped the weather would cool down, but another heat wave threatens human health and increases the risk of wildfires. Along with those hot days and nights, air quality data showed unhealthy levels of pollution.

Sound familiar? This scenario is increasingly the new normal in many parts of the world.

High heat and air pollution are each problematic for human health, especially for vulnerable populations such as the elderly. But what happens when they strike at the same time?

We looked at the more than 1.5 million deaths from 2014 to 2020 recorded in California — a state prone to summer heat waves and air pollution from wildfires — to find out.

Deaths increase when both risks are high

The number of deaths increased both on hot days and on days with high levels of fine particulate air pollution, known as PM2.5. But on days when an area was hit with a double whammy of both high heat and high air pollution, the effects were far greater than for either condition alone.

The risk of death on these very hot, polluted days was about three times greater than the effect of high heat or high air pollution alone.

The more extreme the temperatures and pollution, the higher the risk.

During the 10% of the hottest and most polluted days, the risk of death increased by 4% compared to days without extremes. During the top 1%, it increased by 21%; and in people over the age of 75, the risk of death increased by more than a third on those days.

Why the risks are higher when both strike at the same time

Combined exposure to extreme heat and particulate air pollution can harm human health in several ways.

Oxidative stress is the most common biological pathway linked to particulate air pollution and heat exposure.

Oxidative stress is an imbalance between the production of highly reactive molecules called reactive oxygen species, or ROS, and the body’s ability to eliminate them. It has been linked to lung diseases, among other illnesses.

Antioxidants help scavenge these molecules, but particulate air pollution and heat disrupt this balance through excessive metabolic production of ROS and reduced antioxidant activity.

Our research also showed that the effects of particulate air pollution and temperature extremes were greater when high nighttime temperature and pollution occurred together.

High nighttime temperatures can interfere with normal sleep and potentially contribute to chronic health conditions such as heart disease and obesity, and disrupt the way the body regulates temperature.

Older people may be more susceptible to the effects of exposure to extreme heat and air pollution, in part because this stress is added to chronic age-related health problems like heart disease. , high blood pressure, diabetes or chronic lung disease.

Impaired regulation of body temperature in response to heat can also occur with aging. And older people may be less mobile and therefore less able to get to cooling centers or medical care and be less able to afford air conditioning.

A future of high temperatures and air pollution

It’s not just a California problem. Climate change will increase exposure to high heat and air pollution in many parts of the country.

Average annual temperatures in the United States are already more than 1.8 degrees Fahrenheit (1 degree Celsius) higher than those of the early 1900s.

By the end of this century, global temperatures are on track to increase by almost 5 degrees Fahrenheit (2.7 degrees Celsius). Dangerous extreme heat waves, currently rare, will become more common.

Climate change is also affecting outdoor fine particulate pollution levels – for example, through weather changes such as stagnant air events, wind and dust storms, and drier and warmer conditions that contribute to increasingly frequent and intense forest fires.

What to do to stay safe

Further research is needed to better understand these effects, such as the total impact of exposure to wildfire smoke.

However, there is enough evidence that people should take steps to reduce their risk of harm during times of extreme heat or air pollution.

This means staying well hydrated and staying cool. Shopping malls and other air-conditioned public spaces can provide refuge from the heat. Home air conditioning, especially at night, can reduce mortality. A portable in-room air filter can significantly reduce particulate pollution levels.

People with symptoms of heat stress, such as headache, nausea, dizziness or confusion, especially the elderly, should seek medical attention.

Many county and state health departments already provide alerts about extreme heat and extreme air pollution. The development of a special category of alert during simultaneous extremes can be beneficial for public health.

Governments must also take action now to avoid future worst-case scenarios of climate change. Some best practices for cities include creating cooling shade coverage and green spaces that will also reduce particulate pollution.

Erika Garcia, assistant professor of population science and public health, University of Southern California; Md Mostafijur Rahman, Postdoctoral Fellow and Research Associate in Environmental Health, University of Southern California, and Rob Scot McConnell, Professor of Population and Public Health Sciences, University of Southern California

This article was originally published by The Conversation. Read the original article.