A recent study is the latest to suggest that the impacts of climate change extend beyond extreme weather events and natural disasters by worsening hundreds of infectious diseases. The researchers identified over 1,000 unique ways that climate hazards caused by greenhouse gas emissions influence almost 300 diseases—representing nearly 60 percent of all infectious diseases. 

Hundreds of diseases are impacted by climate change

Greenhouse gas emissions have already impacted every organism on earth. Like humans, any organisms that carry disease, also known as disease vectors, are vulnerable to the effects of climate change, albeit in different ways. For example, warming water, changes in precipitation, and flooding disrupt aquatic ecosystems and affect the behavior of microbes that cause waterborne diseases. Meanwhile, higher air temperatures are increasing the size and range of disease-carrying insect populations.

The study, published this summer, found that rising air and water temperatures; precipitation changes that produce flooding and drought; storms; and loss of natural areas have the most influence on infectious disease. Climate change has the most impact on diseases that spread through water and food (like cholera and E. coli), air (like COVID-19), and direct contact (like polio and monkeypox). 

Climate change forces us into closer proximity to disease vectors

Perhaps the most damaging aspect of extreme climate events is that they force humans into unprecedentedly close contact with disease vectors—and vice versa. “Habitat disruptions caused by warming, drought, heat waves, wildfires, storms, floods and land cover change were … associated with bringing pathogens closer to people,” the researchers write. A study published earlier this year found that climate change increases the risk of “spillover,” the transmission of diseases between organisms of different species. Natural disasters that displace humans also disrupt the habitats of other disease-carrying and disease-causing organisms, forcing these organisms to expand their habitats to survive. When these expansions overlap with human communities, diseases are bound to spill over. 

In a 2013 fact sheet, the U.S. Agency for International Development noted that “nearly 75 percent of all new, emerging, or re-emerging diseases affecting humans at the beginning of the 21st century are zoonotic (i.e. originated in animals).” The list includes HIV, a virus that originated in nonhuman primates as SIV before mutating into a strain that only affects humans; H1N1, or swine flu; and SARS and MERS, the coronaviruses that caused two major outbreaks prior to 2019. In the near decade since the fact sheet was published, the world has seen dozens of zoonotic disease outbreaks, most recently the COVID-19 pandemic and monkeypox outbreaks outside of countries where the virus typically circulates.

Extreme climate boosts pathogens—while harming humans

One of the study’s most troubling findings is that climate change tends to strengthen the pathogens that cause human diseases. Of the 286 pathogens analyzed, only around 3 percent were weakened by climate change. All others either were solely exacerbated by climate change or were exacerbated by some climate hazards but weakened by others. As it boosts disease vectors, climate change impairs humans’ ability to combat the diseases they spread. Displacement, damage to infrastructure, and increased exposure to the diseases caused and worsened by climate hazards put humans at a disadvantage.  

It’s not too late to fight climate change’s effects on disease

Although we’re already experiencing climate change’s impact on disease, there are actions that can help mitigate the effects. The researchers say that the scale of climate change’s disruption underscores “the urgent need for aggressive actions to mitigate [greenhouse gas] emissions.” But reducing emissions will not be enough to slow or reverse our changing climate’s aggravation of infectious disease. Governments will need to invest in disease surveillance and improved infrastructure to reduce disease spread, in conservation and development of natural resources, and in improved monitoring of drinking and wastewater and air quality to protect against the new disease landscapes created by climate change.