Their findings, published on August 8 in Nature Climate Change, reviewed more than 77,000 scientific papers in relation to 10 different climatic events to learn more about how greenhouse gas levels impact currently known infections and diseases. “Given the extensive and pervasive consequences of the COVID-19 pandemic, it was truly scary to discover the massive health vulnerability resulting as a consequence of greenhouse gas emissions,” said lead author Camilo Mora, PhD, professor at the University of Hawaiʻi at Mānoa, in a release. “There are just too many diseases, and pathways of transmission, for us to think that we can truly adapt to climate change. It highlights the urgent need to reduce greenhouse gas emissions globally.”
Climate Change Is Making It Easier for Mosquitos and Ticks to Carry Diseases
To find out how climate change may be affecting diseases, researchers identified 10 climate hazards that are known to be sensitive to greenhouse gas emissions, including warming, drought, heatwaves, wildfires, and extreme rain and flooding. Then they merged two lists of all known infections and pathogens to create a comprehensive list of human diseases. (A pathogen is something that causes disease; germs, viruses, bacteria, and fungi are all pathogens.) Finally, investigators combed through more than 77,000 scientific papers for examples of the climate hazards in combination with each of the known diseases. Warming, precipitation, floods, drought, storm, land cover change, ocean climate change, fires, heatwaves, and sea level changes were all found to influence diseases. The analysis showed that the diseases were mostly transmitted by vectors (organisms that carry pathogens from person to person and place to place, such as mosquitos or ticks), but researchers also found other transmission pathways, including waterborne, airborne, direct contact, and foodborne. Key findings of the study:
More than 58 percent of human diseases caused by pathogens are made worse by climate-related hazards. Investigators found more than 1,000 unique pathways in which climate hazards were in some way connected to impacting pathogenic diseases.Climate hazards bring pathogens closer to people, but not in a good way. Warming and precipitation changes allowed vectors such as mosquitos, ticks, and fleas to cover more territory and infect more humans.Some climate hazards make it easier for some vectors to reproduce and stay alive longer. For example, warmer temperatures in some parts of the world gave the mosquito population a boost. They were able to survive longer, bite more, and more efficiently transmit the West Nile virus.The stress of some climate hazards made it harder for humans to cope with pathogens. For example, flooding or droughts can result in poor sanitation in some parts of the world, which contributes to a rise in illnesses including diarrheal diseases, salmonella, and typhoid fever.
Although most conditions were made worse by climate hazards, 16 percent were actually diminished by greenhouse gas emissions. For example, warming appears to have reduced the spread of viral diseases. The authors theorize that this may be because warmer temperatures create unsuitable conditions for viruses, or because people have a stronger immune response in warmer conditions. Interestingly, most diseases that were reduced by at least one hazard were at other times aggravated by another (and sometimes even the same) hazard, noted the authors.
Experts Call for a Reduction in Greenhouse Gas Emissions, Highlight the Need to Develop New and Better Treatments and Vaccines
“We knew that climate change can affect human pathogenic diseases,” said coauthor Kira Webster, a doctoral student in geography at the University of Hawaiʻi at Mānoa’s College of Social Sciences, in the release. “Yet, as our database grew, we became both fascinated and distressed by the overwhelming number of available case studies that already show how vulnerable we are becoming to our ongoing growing emissions of greenhouse gases.” “I think the findings are not surprising because it is clear that the context in which people live impacts the incidence and prevalence of infectious diseases, and certain climatic conditions can enhance or diminish the force of infection,” says Amesh A. Adalja MD, a senior scholar at the Johns Hopkins Center for Health Security in Baltimore, who was not involved in the research. “But it’s important to recognize that the relationship isn’t always direct. For example, the authors cite warm weather leading to more recreational water activity, which then leads to more waterborne infections,” he says. The findings aren’t necessarily cause for alarm. Rather, they highlight the need to use human technology to minimize the threat of disease by developing new and better diagnostics, treatments, and vaccines for these pathogens, to adapt to whatever degree of climactic change occurs, says Dr. Adalja. “Humans have always used technology to make the environment safer from an infectious disease perspective. Pasteurization, modern sanitation, antibiotics, insect repellents, vaccines, and malaria bed nets are all examples of this phenomenon,” he says.
