Of the 375 known pathogenic diseases that afflict humanity worldwide, 58 percent can be aggravated by climate change, according to a new study in the journal Nature Climate Change. In total, 218 illnesses caused by viral, bacterial, and fungal infections were found to be potentiated by increasing temperatures and other serious climate hazards.
The study authors reviewed over 70,000 scientific papers in search of empirical examples of diseases being influenced by 10 specific climatic hazards. These included warming, heatwaves, droughts, wildfires, extreme precipitation, floods, sea level rise, land cover change, and ocean biogeochemical change.
This extensive review yielded 3,213 case examples in which climatic hazards were implicated in pathogenic disease. Breaking down the data further, the researchers identified 1,006 unique pathways by which infectious pathogens may become impacted by the changing climate.
Many of these mechanisms involved pathogens being brought into closer proximity to humans. For example, wildfires that caused bats and primates to flee their habitats were linked to Ebola outbreaks in Africa, while thawing permafrost may have led to the release of an ancient anthrax strain that caused numerous infections in the Arctic circle.
Conversely, climate hazards that cause the displacement of human populations were found to bring people into closer contact with pathogens. These include storms, floods, and sea level rise, all of which were implicated in cases of Lassa fever, pneumonia, typhoid, hepatitis, cholera, Legionnaires’ diseases, and respiratory disease.
In addition to facilitating contact between people and pathogens, climate change is also enhancing many disease-causing organisms by extending their habitable range and allowing for longer breeding periods. Warming and heavy rainfall, for instance, lead to more food and resources for plague-carrying rodents, allowing populations to grow and increasing the risk to humans. Storms and floods also create stagnant water pools that act as breeding grounds for mosquitoes, leading to outbreaks of yellow fever, malaria, leishmaniasis, West Nile fever, and dengue.
Finally, climate change is impeding humans’ capacity to cope with pathogens by increasing the physical challenges we face while disrupting sanitation and medical infrastructure. Drought, for instance, reduces access to clean drinking water, while heavy rains damage sewage systems and lead to further contamination of the water supply. Such hazards have been implicated in outbreaks of cholera, scabies, Salmonella, E. coli, dysentery, and hepatitis.
Overall, 160 diseases were found to be aggravated by warming, while 122 were affected by precipitation changes and 121 were impacted by floods. Drought aggravated 81 different pathogens, storms affected 71, land cover changes enhanced the threat posed by 61 diseases and ocean climate change was associated with 43 harmful illnesses. Fires, heatwaves, and rising sea levels were found to influence 21, 20, and 10 diseases respectively.
"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 study author Camilo Mora in a statement. To illustrate their point, the researchers have created a website that allows users to examine the ways in which specific diseases are affected by different climate hazards.
"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," said Mora.