A digital billboard displays an unofficial temperature in downtown Phoenix, Arizona, United States Image Credit: AP

Extreme heat has blanketed much of the world this summer. The World Meteorological Organisation reports that July has been the hottest month ever recorded on Earth. The frequency of heatwaves has been steadily increasing in the United States, from an average of two per year in the 1960s to six today.

This pattern is more than just an existential environmental crisis; it is also one that threatens virtually every aspect of human health.

Extreme heat already kills more Americans than hurricanes, floods or any other weather-related emergency. Some of these deaths are the result of heatstroke, which occurs when the ambient temperature is so high that the body loses control over internal regulation. Organ failure can occur within minutes.

For example, in the Phoenix area, where temperatures this summer soared above 110 degrees for more than 30 days in a row, at least 25 people have died from the heat. Another 249 deaths are under investigation. But high ambient temperatures can also exacerbate underlying medical conditions by straining the heart, lungs and kidneys.

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Permanent neurological harm

A review published in Lancet Planetary Health found that heatwaves were associated with an almost 12 per cent increase in mortality from cardiovascular disease. Other researchers have noted correlations between duration of heat events and increased emergency care for kidney disease and chronic lung conditions.

It’s not only physical health that is affected. Spikes in temperature can impair sleep and disrupt brain neurotransmitter function, which impacts mental well-being. Recent studies in the Lancet and Nature Climate Change found that even an increase in temperature of 1 degree Celsius can worsen depression, anxiety and suicide rates. (Climate change itself is a source of mental distress, especially among young people.)

Another result of rising temperatures is that infectious diseases once confined to warmer regions are expanding their reach. An analysis by the Centers for Disease Control and Prevention concluded that the number of illnesses from mosquito, tick and flea bites doubled between 2004 and 2018.

This includes Lyme disease, a tick-borne illness that can inflict permanent neurological harm if untreated, and West Nile disease, an infection spread by mosquitoes that led to at least 127 deaths during an outbreak in the southwestern United States in 2021.

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FILE PHOTO: A woman pours water on a man near the Colosseum during a heatwave across Italy, in Rome, Italy. July 18, 2023. REUTERS/Remo Casilli/File Photo Image Credit: REUTERS

Susceptible to extreme heat

The latest is the alarming re-emergence of malaria in the United States. The parasitic disease, which causes more than a half-million deaths globally each year, is almost entirely confined to regions of Africa. Though there are routinely cases of malaria diagnosed in the United States, they have all been among travellers who acquired it abroad.

This has changed. Over the past few months, there have been seven cases of malaria in Florida and one case in Texas that were all locally acquired. That means individuals were bitten by mosquitoes carrying malaria in their areas.

The risk of contracting malaria within the United States remains very low, but the occurrence of local transmission should be a sobering reminder that diseases associated with other parts of the world can affect us here as weather patterns change. Indeed, at least 200 infectious diseases globally are exacerbated by climate hazards.

There are measures people can take to reduce the negative health impacts of rising temperatures. First, know whether you are among the groups most susceptible to extreme heat.

These include older adults and young children, who have more trouble with thermoregulation, and people with severe underlying medical conditions. Some medications, including certain psychiatric therapeutics, can increase the likelihood of overheating.

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People watch the wildfire on the island Ciovo, from Seget Gornji, Croatia, July 27, 2023. Image Credit: REUTERS/

Impact of changing weather

Second, have a plan for getting through extreme heat events. How much heat you can tolerate depends on your individual circumstances. When in doubt, exercise caution and stay in air-conditioned spaces.

Check on elderly neighbours. Find out where you can access community resources such as cooling centres and pack a “go-bag” just in case. And know where you would go to seek medical care, and make sure those around you are aware of your preference.

Third, change elements that are within your control. Be aware of the impact of changing weather on your sleep and the implications for your mental health. Monitor your use of substances, including alcohol, that can blunt your body’s thermoregulation.

Reduce your risk of vector-borne diseases by wearing long sleeves and pants in areas known to have ticks and by removing standing water and other mosquito breeding grounds.

On a systemic level, every sector — including the health-care industry — must examine how to reduce their contributions to global warming. There is no denying that climate change is now a public health crisis. The health impacts we are already experiencing will multiply for our children, grandchildren and generations to come. — Washington Post

Leana S. Wen is a professor at George Washington University’s Milken Institute School of Public Health