In 1994, Jonathan Patz, MD, MPH, was the first to facilitate a session about climate change for the American Public Health Association.

Robeznieks A. Why physicians see climate change as a health emergency. American Medical Association. September 20, 2019.

Met with skepticism at the time, the concepts have yielded to emerging evidence nearly 30 years later confirming the relationship between climate change and disease emergence.

 

As the planet changes, the likelihood of cross-species viral transmission—the event that most likely led to the COVID-19 pandemic—increases.

Holmes EC. COVID-19—lessons for zoonotic disease. Science. 2022;375(6585):1114–1115.

 

 

Climate change and zoonotic viral spillover

There is convincing evidence that the COVID-19 pandemic was caused by a zoonotic viral spillover incident, in which a virus jumped from animals to humans. It won’t be the last of its kind, however, if climate change persists, according to a 2022 report published by Nature.

Carlson CJ, Albery GF, Merow C, et al. Climate change increases cross-species viral transmission risk. Nature. Published online April 28, 2022:1–1.

 

Wild mammals carry over 10,000 viral species that could potentially infect humans. Historically, humans haven’t come into contact with most of these mammals, mitigating the risk of disease emergence.

But the effects of climate and land-use change could converge to create viral-sharing hotspots between wild animals and humans. If the rate at which Earth is warming is maintained, then by 2070, there will be new aggregations of mammal-virus species in certain places, such as higher elevations, environments with higher biodiversity, and Asian and African territories with dense human populations.

The result of humans and animals living in close quarters in new combinations will lead to a higher frequency of cross-species viral spillover. Bats, in particular, due to their unique dispersal capacity, are prime suspects for novel virus-sharing with humans.

The authors of the Nature study note that this projected outcome isn’t as far off as it seems.

“Surprisingly, we find that this ecological transition may already be underway, and holding warming under 2 °C within the century will not reduce future viral sharing,” they wrote.

“Our findings highlight an urgent need to pair viral surveillance and discovery efforts with biodiversity surveys tracking species’ range shifts, especially in tropical regions that harbor the most zoonoses and are experiencing rapid warming.”

 

Natural disasters, ice melting, and disease emergence

A Cleveland Clinic article states that extreme weather such as droughts and hurricanes can displace wild animals, bringing them into closer contact with domestic animals and humans.

How climate change may affect future pandemics. Cleveland Clinic. April 21, 2021.

 

Polar ice melting is also a potential concern. Long-dormant viruses could surface as a result of thawing ice in polar regions, potentially infecting humans.

Global warming could also bring about a rise in mosquito-borne illnesses, in addition to the emergence of zoonotic disease.

 

Addressing the root cause can improve health outcomes

The American College of Physicians has developed a Climate Change Toolkit for physicians, with recommendations for actions you can take to address climate change.

Climate Change Toolkit. American College of Physicians. 2021.

 

• Be an advocate for policy change. Use your voice to ask for climate change adaptation and mitigation policies. The widespread use of clean and renewable energy sources will not only slow climate change, but also improve air and water quality.

• Promote clean energy use. Ditch fossil-fuel–generated electricity for clean energy sources. The resulting reduction in air pollution will lead to lower rates of certain respiratory and cardiovascular illnesses among patients.

• Encourage use of active transportation methods. Physicians, as well as patients, can try cycling or walking, if possible, instead of using gas to drive a short distance. This can also improve cardiovascular health.

• Buy locally sourced foods. Reduce carbon pollution and enhance your cardiovascular health by limiting meat intake and sourcing fruits and veggies locally.