Climate change-related weather hazards linked to nearly 60% of human diseases

Everyone knows rats, bats, mold and mosquitoes can make people sick, but a new study out this week concludes such pathogens and hundreds more are made worse by the warming world. 

A group of University of Hawaii researchers put together a list of 376 human diseases and allergens, then looked at how they're affected by climate-related weather hazards, such as heat waves, flood, drought, fire and rain. 

They found nearly 60% of the known pathogens that make people sick have been aggravated by warming-related weather hazards, according to the study published this week in Nature Climate Change. The list included not only mosquito-borne viruses like malaria and dengue fever but also asthma, monkeypox, shellfish poisoning and even fungal infections like valley fever. 

A new study out this week concludes weather disasters made worse by the warming climate are aggravating a host of pathogens that make people sick.  Here, an area of homes are submerged by a flood along the North Fork of the Kentucky River in Jackson, Kentucky on July 28.

The researchers reviewed more than 70,000 academic studies and papers to search for links between the pathogens and 10 climate-related weather hazards.

“The results were truly sobering,” said Erik Franklin, assistant professor at the university's Hawai'i Institute of Marine Biology and a study co-author.

Climate hazards are bringing pathogens and people closer together, strengthening the pathogens and impairing people, Franklin said. “This is a massive vulnerability for human health care systems.”

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Pathways to disease

Even after sounding warnings about the consequences of climate change on human health for more than 25 years, Jonathan Patz, a professor at the University of Wisconsin-Madison’s Nelson Institute, was still surprised at the many ways researchers found climate hazards affect disease.

“They found over 1,000 unique pathways," said Patz, also a co-author of the study. "That to me was striking.”

The pathways included things like flood-transmitted disease and mosquitoes that thrive in heavy rainfall, spreading malaria and other diseases. Warming, rainfall and flooding were the three most frequent pathways pathogens could be transmitted to people.

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What do the findings mean?

“It just amplifies the key message that the climate crisis is a human health crisis,” Patz said. “When we’re talking about 58% of all infections and other human pathogenic diseases being affected by climate, it demands that we shift our attention away from thinking about every single disease and vaccine."

The study reveals “worrisome glimpses” into the possible consequences of health crises in the future and points to an “urgent need” to reduce fossil fuel emissions that cause the planet to warm, Franklin and others said.

“There are just too many diseases and pathways of transmission for us to think that we can truly adapt to climate change," said co-author Camilo Mora, geography professor in the University of Hawaii's College of Social Sciences. "It highlights the urgent need to reduce greenhouse gas emissions globally.”

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Were any of the diseases diminished by climate hazards?

The study found 63 pathogens had been diminished at some point by climactic hazards, such as cases in which warming reduced the spread of viral diseases. All but nine of those had also been aggravated at some point by climate, however. 

The authors cautioned that their work could reflect a bias, based on what the authors published in Google Scholar chose to study. For example, researchers may be doing more studies about diseases aggravated by the changing climate or fewer studies about diseases less concerning because of climate change. 

Have other recent studies looked at the effect of warming on pathogens? 

Yes. More than a half-dozen studies this year, including two this week, have pointed out the rising risk of disease transmission in a warming world.

Another study out this week, led by Mia Maltz, a microbial ecologist at the University of California, Riverside, found higher concentrations of dust carrying toxins from around the world are landing at lower elevations in the Sierra Nevada mountains. The study also concluded increasing droughts could spread more pathogens in dust.

“Pathogenic dust is becoming more of a threat as the Earth gets drier and more parched," Maltz said. 

Weather hazards such as dust storms can transport disease pathogens to new locations and could be made worse by the warming climate, experts say.  This dust storm swept over Sioux Falls, South Dakota, earlier this year.

A study in April co-written by Colin Carlson, a global change biologist and assistant research professor at Georgetown University, and a group of collaborators found that changes in climate and land use could bring previously isolated wildlife species – and their pathogens – into new areas. 

Carlson and others also have documented rapid range shifts in African anopheles mosquitoes over the past century. The researchers question the role climate change might have played and suggested it's an important topic for future research. 

A co-author on another study, Dr. Aaron Bernstein, interim director of the Center for Climate, Health, and the Global Environment at Harvard School of Public Health, told The Associated Press the Hawaii study is a good warning as warming and habitat loss push animals and their diseases closer to people.

“This study underscores how climate change may load the dice to favor unwelcome infectious surprises,” Bernstein told the AP in an email. “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.”

What happens next? 

The University of Hawaii researchers put together an elaborate interactive website others can use to see the links between climate-related hazards and pathogens. 

"We're hoping it's a much more useful tool," Franklin said. "We're hoping it will be a resource for health care practitioners to use in their own work." 

See the connections to climate:Impacts of climate change on human disease

Contributing: The Associated Press

Dinah Voyles Pulver covers climate and environment issues for USA TODAY. She can be reached at or at @dinahvp on Twitter.