Climate change may make pandemics like COVID-19 much more common

The likelihood of an extreme epidemic, or one similar to COVID-19, will increase threefold in the coming decades, according to a recent study published in the Proceedings of the National Academy of Sciences.

The researchers used data from epidemics from the past 400 years, specifically death rates, length of previous epidemics and the rate of new infectious diseases. Their calculation is a sophisticated prediction based on known risks and can be a useful guide for policy makers and public health officials.

They also found that the probability of a person experiencing a pandemic like COVID-19 in one’s lifetime is around 38%. The researchers said this could double in years to come.

The probability of another pandemic is "going to probably increase because of all of the environmental changes that are occurring," Willian Pan, an associate professor of Global Environmental Health at Duke University and one of the study's authors, told ABC News.

Scientists are looking closely at the relationship between climate changes and zoonotic diseases, like COVID-19.

Climate change and zoonotic diseases

Zoonotic diseases are caused by germs that spread between animals and people. Animals can carry viruses and bacteria that humans can encounter directly, through contact, or indirectly, through things like soil or water supply, according to the Centers for Disease Control and Prevention.

"As you make that interface between humans and the natural world smaller, we just come in more contact with those things and climate enhances the ability for viruses to infect us more easily," said Pan. He said our risk for any zoonotic or emerging viral infections is going to rise over time.

An example of this is the recent outbreak of Ebola in West Africa.

"There's evidence that there is loss of forests in West Africa for palm oil. There's a whole story around the palm oil industry, destroying forest tropics to plant palm oil trees," said Dr. Aaron Bernstein, director of the Climate MD program at the Center for Climate, Health, and the Global Environment at Harvard University’s Chan School of Public Health.

"In this case, there are bats that live in those forests but they can't live in palm oil plantations. And so those bats moved to a part of West Africa where they infected people with Ebola," said Bernstein.

Zoonotic diseases now account for 60% of all diseases and 75% of emerging diseases, according to the CDC.

"More animals come into contact with more people but they also, in many cases, have resulted in animals bumping into other animals," said Bernstein. "What we've observed is that animals and even plants are racing to the poles to get out of the heat. And as they do that, they may run into creatures that they've never run into before. And that creates an opportunity for spillover to happen."

Looking ahead

Currently, scientists are playing catch up with viral outbreaks by racing to create vaccines, sometimes after an outbreak is already out of control.

"We can't deal with pandemics with Band-Aids. Meaning after waiting until diseases show up, and then trying to figure out how to solve them," said Bernstein.

Added Pan: "Globally, if we want to prevent another major pandemic from completely disrupting our society, we need to start investing heavily and sharing information across countries on surveillance of different viral infections. There's some places in the world where we don't even have the basic capacity to evaluate or test strains, viral fevers coming into hospitals. And so a lot of those things go unchecked until it's too late."

Preventing these diseases not only requires global collaboration, but attention to the source of the problem.

"We need to address spillover. And that means we need to protect habitats. We need to tackle climate change. We need to address the risk of large-scale livestock production because a lot of the pathogens move from wild animals into livestock and then into people," said Bernstein.

Global spending on COVID vaccines is projected to reach $157 billion, according to Reuters. Annual spending on forest conservation is much less.

"We're about to throw a whole lot of money at solutions that only address a fraction of the problem. We get very little back relative to what we could get back for $1 spent on post spillover intervention versus root cause prevention," said Bernstein.

Emma Egan is an MPH candidate at Brown University and a member of the ABC News Medical Unit.