How Climate Change May Have Driven COVID’s Emergence

A boost to forests in otherwise clement conditions was expected, but their contribution to the spread of aviating mammals and zoonotic diseases was not quite as obvious

Ruth Schuster
Ruth Schuster
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A fruit bat
A fruit batCredit: Haim Ziv / Weizmann Institute
Ruth Schuster
Ruth Schuster

Here’s one we didn’t see coming. Climate change may have driven the emergence of the virus behind COVID-19 through encouraging forest growth in rain-rich areas, contends a study published last week in the journal Science of the Total Environment.

By “emergence,” that means the virus likely existed before but newly came to our attention, because it made the leap from some animal to human beings, and spread.

How did climate change lead to 106 million known global cases and 2.3 million deaths from COVID (as of Sunday morning, according to the Worldometer)?

Over the last century, carbon dioxide and other greenhouse gas emissions began to drive climate change, expressed among other things in global warming. Carbon dioxide and warmth are beneficial for trees, everything else being the same.

The result was that the vegetation in southern China (and next-door Myanmar and Laos too) significantly changed, from predominantly shrubland to savannah, and trees in Yunnan, southern China, too while about it.

A fruit bat living up to its name.Credit: Merlin D. Tuttle / Bat Conservation International

Bats were delighted. The changes were exactly to their taste, given their predilection for forest living, explains the University of Cambridge.

No, it has not been categorically proven that SARS-Cov-2 – the viral agent behind the disease we call COVID-19 (for the year of its discovery, not the number of coronavirus species out there) – is from bats. It may be. It may not be. It may have leaped from bats, or another species, to humans in so-called wet meat markets in Wuhan, or through another animal intermediary such as the pangolin, civet or other.

Coronavirus is a whole family of viruses. The common cold is caused by coronaviruses. Bats are suspected – not proven – to have been the origin of more than one type of coronavirus that have reached humankind, including the first SARS, MERS (Middle East respiratory syndrome), and now COVID.

Also: the more bat species a given area has, the more types of coronavirus are there, write authors Robert Beyer of the University of Cambridge with Andrea Manica of the Potsdam Institute for Climate Impact Research, and Camilo Mora of the University of Hawaii. “The number of CoVs present in an area is strongly correlated with local bat species richness, which in turn is affected by climatic conditions that drive the geographical distributions of species,” they write. And there you have it.

How significant is this? Well, global temperatures have risen by over a degree on average, carbon dioxide has reached levels last seen millions of years ago and a cool 40 more bat species have moved into the Yunnan province in the past century, harboring roughly 100 more types of bat-borne coronavirus, the authors say.

Civets caged for exploitationCredit: Liu Dawei / AP

It is this area of Asia, where the vegetation and bats are thriving, that SARS-Cov-2 almost certainly arose.

Bats are incredible little creatures, or incredible big ones if we factor in the Australian flying fox, which can have a wingspan of over 1.5 meters (4 foot 11 inches). Bats are the only aviating mammal, they have excellent spatial memories, the fruit bats among them at least have the power of speech and carry on whole conversations – which researchers suspect is largely devoted to bitching at one another.

The list of their wondrous characteristics could go on for a long time. But it is also believed that, among all the mammals, bats carry more zoonotic viruses, which can infect us.

The Washington Post ran a story in 2017 on why bats can carry so many diseases that can infect us, including possibly Ebola, without getting sick themselves. The answer appears to lie in their beefed-up immune system response to viral infection and ability to tame inflammation.

A pangolin.Credit: Mint Images / AP

None of this is proof that the disease ravaging the world originated in bats, but this is an intriguing correlation and is the first paper directly linking climate change to the coronavirus, albeit through a chain: climate change, global warming, emissions, boosts to forests, bats like forests, people cut down trees and otherwise encroach on animal habitats, and like eating bats, whether roasted or in soup.

The bottom line is that the more we encroach on natural habitats, the more viral and other diseases we are likely to encounter in the animals living there, and the likelier we are to catch these diseases and then spread them.

We are much less likely to develop immune responses like the bat, and the solution cannot lie in killing every animal that might inconvenience us. So what can we do? Behave.

“To reduce the risk of future zoonotic spill-overs, it is crucial to introduce measures to protect natural habitats, impose strong regulations on wildlife hunting and trade, establish appropriate animal welfare standards on farms, markets and transport vehicles, and discourage high-zoonotic-risk dietary and medicinal customs,” the authors say.

In other words: the answer must lie in curbing our appetites and adhering to basic hygienic principles.

The Australian flying fox, which can have a wingspan of over 1.5 meters.Credit: Rob Griffith / AP
The fruit bat: not just a pretty face.Credit: Ezra Hadad