Photomicrograph of anthrax.
The microscopic rod-shaped Bacillus anthracis bacterium that causes anthrax is one pathogen worsened by drought, heat waves, and heavy rainfall, according to studies reviewed by the latest research. Credit: PD-USGov-HHS-CDC, Public Domain

The consequences of climate change aren’t reserved for the oceans and atmosphere: Diseases have secured a larger presence in recent years thanks to global warming.

“That was quite shocking to all of us.”

In a sweeping analysis of more than 800 published studies, scientists from the University of Hawai‘i at Mānoa (UHM) discovered climate change had exacerbated 58% of infectious diseases in certain documented instances. Although less common, climate warming also lessened 16% of infectious diseases.

“We never imagined the magnitude of diseases impacted by climate change. I think that was quite shocking to all of us,” said coastal hydrologist Tristan McKenzie at the University of Gothenburg, Sweden. McKenzie completed the work with others during his doctorate at UHM.

The illnesses aggravated by climate change include some of the deadliest, such as measles, malaria, and diarrheal diseases. Scientific literature has long supported the fact that climate change enhances certain diseases, such as a study earlier this year finding that bacteria-caused diarrhea could become more dominant as wetter and warmer conditions spread.

However, “this is the first paper to really comprehensively try and put together the full picture,” said McKenzie.

Warming temperatures, changes in precipitation, and floods worsened the highest numbers of diseases. These factors were followed by other hazards associated with climate change, including fires, storms, sea level rise, ocean climate change, heat waves, drought, and changes to land cover.

Climate’s Contagion

In Scandinavia in 2014, an outbreak of cholera, a warm-water disease, shocked observers.

Sifting through more than 77,000 titles in the scholarly literature, researchers found that warming stood out as a key escalator for infectious diseases.

In Scandinavia in 2014, an outbreak of cholera, a warm-water disease, shocked observers. An aggravating factor was an unusual heat wave that crept to within 160 kilometers of the Arctic Circle that summer, warming the ocean’s surface waters. That same warm water provided a breeding ground for Vibrio bacteria. When unknowing people encountered the infected seawater or ingested it, it gave them infectious and sometimes fatal diarrheal diseases, like cholera.

A team of ocean and public health researchers recounted the Scandinavian outbreak in the journal of Emerging Infectious Diseases in July 2016, and that is just one of the published works that fed the latest research.

In total, the study found that warming aggravated 160 diseases.

On the flip side, warming diminished some diseases. Warming winters in Ontario, Canada, for instance, led to fewer pneumonia cases among people over 65, according to a 2007 Social Science and Medicine study conducted by a group of Canadian geographers and health experts.

The UHM team created an interactive visualization of climate’s effects on diseases and published their findings in the journal Nature Climate Change this month.

A Conservative Crystal Ball

Although the literature review excluded future projections, McKenzie views the latest results as a conservative estimate.

“In a lot of cases, disease outbreaks will be poorly documented, particularly for rare diseases,” McKenzie said. “I can only imagine that this will worsen in the future.”

A modeling study out earlier this year in Nature suggests that the number of viruses crossing between species will increase in the coming years as climate change alters the geographic ranges of thousands of mammals worldwide.

Epidemiologist and spatial demographer Josh Colston at the University of Virginia School of Medicine said that the latest study sorted through a “tremendous amount of information.”

“Looking at basically all the climate effects and all the infectious pathogens in one paper is extremely ambitious,” said Colston.

“We need to aggressively reduce greenhouse gas emissions.”

Although McKenzie called the study’s findings “terrifying,” he said they also crystalized the most important solutions.

“A lot of people want to try to take the Band-Aid approach to this,” McKenzie said. But he doesn’t see the point in that. “We need to aggressively reduce greenhouse gas emissions.”

Ramping up wind and solar as well as cutting food waste are two of many cost-effective options for cutting greenhouse gases that enjoy widespread public support, according to the Intergovernmental Panel on Climate Change.

—Jenessa Duncombe (@jrdscience), Staff Writer

Citation: Duncombe, J. (2022), Climate change has already aggravated 58% of infectious diseases, Eos, 103, Published on 23 August 2022.
Text © 2022. The authors. CC BY-NC-ND 3.0
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