How climate change and wildlife influence the coronavirus

By the numbers: Zoonotic diseases — those spread from animals to humans — have “quadrupled in the last 50 years, mostly in tropical regions,” according to a letter more than 100 wildlife and environmental groups sent to Congress this week.

• The groups asked lawmakers to direct 1% of stimulus funds — about $20 billion — to address the loss of animals' natural habitat and wildlife trade, which they consider "the root causes of the problem." It ultimately wasn’t included.

How it works: “We know that tropical diseases tend to have wildlife as reservoirs more than temperate diseases,” said Lee Hannah, a senior scientist in climate change biology at the nonprofit Conservation International.

• Bats and pangolins (scaly anteaters) have especially been linked to this coronavirus and prior ones.
• So when you take animals like that out of the wild and move them into cities, “you’re taking something that’s known to be a wildlife disease reservoir and putting it into a densely populated area,” Hannah said. “As we’re seeing, that’s just crazy.”

Where it stands: China announced late last month it was permanently banning wildlife trade and consumption, according to The New York Times, but conservation experts nonetheless say loopholes still exist and illegal trading could increase, per the Times.

The big picture: Scientists say these types of close encounters with disease-carrying animals are just one part of a complex relationship between humans and nature. Climate change has a massive, overarching impact on it all, though it’s a less direct connection than, say, wild animal markets.

To the degree climate change is connected to infectious diseases, it’s in these indirect ways:

• Air pollution, largely from fossil-fuel emitting sources that also drive climate change, is a key factor that worsens any given virus’ impact on human health, according to Aaron Bernstein, a pediatrician and director of Harvard University’s Center for Climate, Health, and the Global Environment.
• A study of the 2003 outbreak of the Severe Acute Respiratory Syndrome (SARS) in Asia found that “people exposed to the highest level of air pollution were twice as likely to die from the disease as those who were not,” Bernstein said.
• Increasing temperatures could change the habitat for disease-carrying mosquitoes, such as with Zika, into more northern locales, Bernstein says. That’s unlikely to spread so quickly like COVID-19, the illness stemming from the coronavirus, because Zika is primarily spread via mosquitoes.

• Deforestation, which is linked to increased carbon dioxide emissions, also destroys wildlife habitat, which increases the risk of close human-animal encounters, according to Bernstein.

The intrigue: Other strains of infectious viruses, like the seasonal flu, often peak in the winter, partly because people spend more time inside in closer quarters. Scientists are still studying whether this coronavirus will behave like that when it comes to warmer weather.

• Could climate change, which is increasing temperatures around the world, paradoxically help make viruses like COVID-19 less terrible? Don’t bet on it, experts say.

“They [coronaviruses] might become slightly less infectious under conditions where people are outdoors more in warmer climates. There may be an element of truth in that, but I don’t think we can rely on climate change to save us from COVID-19.”

The bottom line: The indirect impact of climate change on infectious diseases far outweighs any potential indirect positive.

Editor's note: This piece was clarified to better explain the impact of deforestation and how Zika works.