Climate change is basically messing up everything in our lives. It’s tempting to find a way to pin the coronavirus pandemic on it, and a new study released today does just that, claiming that climate change “may have driven the emergence” of coronavirus. But it may be more complicated than it seems at first blush.
Scientists have known for a while that changes in habitat, including those precipitated by climate change, can cause humans to come into closer contact with wild animals that may be carrying dangerous viruses. The new study, released on Friday in Science of the Total Environment, takes a much more specific look at how climate change may have shifted the makeup of bat habitats. Changing ecosystems along the China-Laos border, the study says, increased the number of bat species living there, and upped the chances of a disease being passed on to humans.
“Understanding how the global distribution of bat species has shifted as a result of climate change may be an important step in reconstructing the origin of the covid-19 outbreak,” lead author Robert Beyer, a researcher in the University of Cambridge’s zoology department, said in a press release.
Some wild animals are common transmitters of diseases that can be harmful to humans, like coronaviruses, ebola, and rabies. Bats in particular seem to be a warning sign for humans when it comes to viruses: The world’s bats carry around 3,000 different kinds of coronavirus, and research has shown that there’s a positive correlation between the number of types bat species that live in a particular area and bat-to-human disease transmission. This likely isn’t a special evil superpower unique to bats: Researchers have established that the more species an animal group has, the more different viruses they can host. Bats just happen to have a lot of different species.
Climate change has shifted ecosystems around the world as rising temperatures and changing rainfall patterns create different assemblages of plants and animals. What was a lush tropical forest in the 1800s now may be filled with very different types of flora and fauna. That’s the case, the study says, in forests in southern China and along the border with Myanmar and Laos.
The researchers created a map of what the world’s vegetation may have looked like 100 years ago using temperature, precipitation, and cloud cover records, and filled in this map with the habitat needs of different bat species. They then compared this information to current vegetation and data on bat populations to conclude that the changes in habitat may have prompted around 40 different species to migrate to the area along the China-Laos border.
Each bat carries, on average, 2.7 different different types of coronavirus, the study says. The study goes on to posit that when those 40 species migrated beyond their original habitat over the past 100 years, they toted along with them around 100 different versions of coronaviruses, upping the chance of cross-species infection.
In concept, this theory is an alluring one. It’s clear the climate crisis is having a massive impact on the natural and built worlds. And it feels like a pretty straightforward explanation of how our warming planet may have shifted a deadly virus closer to human contact. But just because it feels straightforward may not make it correct.
“It is undeniable that global change including climatic change, land use change, and demographic change will affect emerging pathogen risk,” Rachel Baker, a research scholar at Princeton University’s Environmental Institute who wasn’t involved with the study, said in an email. “However, finding a causal relationship between these changes and the emergence of a specific pathogen, such as SARS-CoV-2, is tricky thing to do.”
She noted that while climate change can make weather events like hurricanes or wildfires more common or extreme, it’s not the only thing causing them. So it is with the virus. Attributing it to climate change “is much harder to do with viral emergence, as you have to account more many more factors.”
Baker pointed out that the study is also not clear on how exactly how more bat species in an area actually impacts bat-to-human disease transmission. The methodology did not use any specific on-the-ground observations on bat populations, just habitat and species range data. That means it lacks a key piece of the scientific puzzle that is needed to support its strong assertions.
“While climate change is one piece of the puzzle, there have been many changes to human society over the past 100 years that have likely elevated the risk from emerging pathogens,” Baker said.