Aug. 9, 2022 – Climate hazards – such as flooding, heat waves, and drought – have deepened the effects of more than half of the known infectious diseases in humans, including anthrax, cholera, and malaria, according to a new study published in Nature Climate Change.
Infectious diseases have long been linked to weather events and climate change, but scientists are now beginning to understand the broad influence of extreme weather on human health.
“If climate is changing, the risk of these diseases are changing,” Jonathan Patz, MD, one of the study authors and director of the Global Health Institute at the University of Wisconsin-Madison, told The Associated Press
Patz and colleagues searched for real examples of the effects of 10 climate hazards that are sensitive to greenhouse gas emissions on known human diseases caused by germs.
The research team found that 218 of 375 infectious diseases found worldwide, or 58%, have been worsened by climate hazards at some point. Real cases revealed 1,006 unique pathways where climate hazards led to these diseases.
In some cases, people became infected through disease-carrying mosquitoes, rats, and deer after extreme rain and floods. In other cases, warmer oceans and heat waves led to tainted seafood. Droughts caused changes in bat habits, which led to viral infections among humans.
The ways that these diseases are spread are “too numerous for comprehensive societal adaptions, highlighting the urgent need to work at the source of the problem,” which means reducing greenhouse gas emissions, the study authors concluded.
The research team also expanded its search to look at all types of human illnesses – including non-infectious diseases such as asthma, allergies, and animal bites – to find out how many health issues could be linked to climate hazards in some way.
They found 286 unique illnesses, including 223 that seemed to be worsened by climate issues. Another 54 illnesses had cases that were both worsened and lessened by climate hazards, and nine were diminished by climate changes.
The study couldn’t analyze the specific disease changes due to climate change, such as higher risks or magnitudes, the AP reported, but the cases showed that extreme weather was a likely factor.
“There is no speculation here whatsoever,” Camilo Mora, PhD, the lead study author and a climate data analyst at the University of Hawaii, told the AP. He noted an important highlight: The study wasn’t about predicting future issues.
“These are things that have already happened,” he said.
Mora himself got chikungunya, a virus spread by mosquitoes, after his home in rural Colombia was flooded 5 years ago. Although he recovered, he continues to feel joint pain, he said.
Mora also pointed to a 2016 case in Siberia, where an old reindeer carcass was unearthed as the permafrost thawed due to warming. A child touched the carcass, which had anthrax, and the child contracted anthrax, starting an outbreak in the region for the first time in 75 years.
Mora at first wanted to study medical cases to understand how COVID-19 related to climate hazards, the AP reported. He found cases where extreme weather both aggravated and lessened the chance of getting the coronavirus. In some situations, extreme heat in poor areas forced people to congregate to cool off, which led to exposure. In other cases, heavy rains reduced the chance of spread because people stayed home and indoors.
Although more studies are needed to show direct links between climate change and many infectious diseases, public health experts told the AP that the study provides a warning about climate effects and human health.
“This study underscores how climate change may load the dice to favor unwelcome infectious surprises,” Aaron Bernstein, MD, interim director of the Center for Climate, Health and the Global Environment at the Harvard T.H. Chan School of Public Health, told the AP.
“But of course, it only reports on what we already know, and what’s yet unknown about pathogens may be yet more compelling about how preventing further climate change may prevent future disasters like COVID-19,” he said.