The consequences of climate change—including warming, drought, and sea-level rise—worsen most infectious diseases by facilitating transmission and increasing the severity of outbreaks, according to a study published today (August 8) in Nature Climate Change. The study finds that climate change has the potential to exacerbate outbreaks of 58 percent of the 375 pathogens that have infected humans in recorded history.
“Systems have been evolving for millions of years and now humans have come along and changed things,” study coauthor Camilo Mora at the University of Hawai‘i at Mānoa tells NBC News, adding that “we are punching nature, but nature is punching us back.”
To assess the impact of greenhouse gas emissions on disease, Mora and his colleagues analyzed more than 3,200 published scientific works, identifying outbreaks reported as having been intensified by at least one climate hazard, such as drought. Tallying the pathogens that cropped up in that evaluation, the study authors found that 217 were also listed in databases of known infectious diseases compiled by the Global Infectious Diseases and Epidemiology Network and the Centers for Disease Control and Prevention (CDC), they write in their paper. The researchers then went on to map pathogenic microbes to climate change outcomes that have the potential to worsen outbreaks, finding that warming temperatures, flooding, and severe precipitation were linked to worsening outbreaks of the most pathogens, while rising sea levels was associated with exacerbating outbreaks of the fewest types of pathogens, reports New Scientist.
“There is no speculation here whatsoever. These are things that have already happened,” Mora tells the Associated Press.
While some diseases can be diminished by climate change—such as how warmer temperatures are less conducive to the spread of influenza—the study authors argue that the majority of pathogens will thrive under climate change conditions through a variety of mechanisms: Warming temperatures, for example, could expand the geographic range of some microbes while also increasing the population sizes of disease-spreading mosquitos. In addition, the authors write that the consequences of climate change could hinder people’s ability to fight infection—for example, severe weather events might damage infrastructure and impede access to food, leading to malnutrition that could dampen immune system function.
“However, correlation is not causation,” Kristie Ebi, a climate and public health expert at the University of Washington who was not involved in the study, tells the AP. “The authors did not discuss the extent to which the climate hazards reviewed changed over the time period of the study and the extent to which any changes have been attributed to climate change.”
Other experts, including Aaron Bernstein of the Center for Climate, Health, and the Global Environment at Harvard School of Public Health, tell the AP that the study is a warning about the ongoing connection between climate and health, particularly as habitat loss increases the number of spillovers of pathogens into humans from other species. “This study underscores how climate change may load the dice to favor unwelcome infectious surprises,” Bernstein writes in an email to the AP.