Are Climate-Driven Shifts in Bat Diversity to Blame for COVID-19?

Other experts say these findings should be interpreted with caution because the predictions are difficult to verify. “Overall I’m not convinced the analysis is robust enough to draw the conclusions asserted,” Matthew Struebig, a conservation scientist at the University of Kent who was not involved in the research, tells The Scientist in an email.

We know that these shifts in species’ ranges can play a critical role in the transmission and evolution of harmful viruses.

—Robert Beyer, Potsdam Institute for Climate Impact Research

Compared with other mammals, bats carry more than their fair share of potentially zoonotic viruses, pathogens that could infect humans. Each species of furry flier hosts an average of 2.7 coronavirus strains, according to one estimate. It follows that as bat diversity increases in a region, so too does the diversity of these spike-studded viruses. If climate change has altered the distribution of bats—and the pathogens they carry—this could influence the likelihood of a disease jumping to humans, Beyer and his colleagues hypothesized.

“It’s a numbers game,” says Sarah Olson, a wildlife epidemiologist at the Wildlife Conservation Society in New York who wasn’t involved with the research. “The more [viral] diversity you have, the more likely it is for viruses to emerge that have the potential to infect humans.”

To estimate how global bat diversity changed between 1901 and 1930 and between 1990 and 2019, Beyer and his colleagues used estimates of temperature, precipitation, sunshine, and carbon dioxide levels to predict global distributions of different vegetation types. By comparing vegetation maps with the habitat requirements and geographic limits of all known bat species, the team predicted total bat species richness at each time period.

Based on this analysis, the team identified several regions where bat diversity may have increased the most: Central Africa, scattered patches in Central and South America, and a large area in southeast Asia, which includes parts of Myanmar, Laos, and China’s Yunnan province. In that Asian region, the researchers estimated that climate change has converted large swathes of tropical shrublands to tropical savannas and deciduous woodland, thereby making the region more suitable for an additional 40 bat species—and around 100 extra coronavirus strains. Because this estimated bat hotspot matches the regions where both SARS-CoV-1 and SARS-CoV-2 are believed to have emerged, the researchers speculate that climate change may have contributed to the emergence of these viral outbreaks.

Olson says that the study is “pushing us to think about drivers of emerging infectious diseases in some new ways.” But, she adds, the findings are speculative and “difficult, if not impossible, to validate.” The study’s conclusions rely on estimates of vegetation for the 1901–1930 time period that cannot be corroborated by satellite or on-the-ground data, says Olson. And because the study relied on climate data to estimate habitat types, it did not consider land-use changes, which could alter the suitability of areas for bats.

Struebig says that he is skeptical of the study’s link between climate change and bat diversity. “There are too many assumptions for me to conclude that climate change could have increased the likelihood of the pandemic occurring in this way.”

Struebig says that the analysis relies on bat distribution data from the International Union for Conservation of Nature (IUCN). “As a member of the IUCN Bat Specialist Group I can tell you that the information we have available to map distributions is grossly insufficient. Many species are not fully assessed, and . . . very little is known about optimum or preferred vegetation types. . . . The study estimates the bat fauna of southern China and neighbouring countries increased by a whopping 40+ species in around 120 years. To put that into perspective that would mean the number of bat species in Myanmar doubled in little over a century! Simply looking back at old species accounts and ecological studies from the region shows this simply did not happen.”

Olson says that although the findings don’t provide conclusive evidence that bat distribution influenced the pandemic, the study helps draw attention to the issue. “We’re altering environments in ways we don’t really understand or appreciate until we have an event like [the COVID-19 pandemic] that makes us reassess our relationship with nature,” she says. “I think [the study] kind of opens the door and says, ‘Hey, here are some other ways that we’re impacting the environment that might be altering the distribution and richness of species.’ And we need to pay attention to that when it comes to [understanding] emerging infectious disease risk moving forward.”

R.M. Beyer et al., “Shifts in global bat diversity suggest a possible role of climate change in the emergence of SARS-CoV-1 and SARS-CoV-2,” Sci Total Environ, doi:10.1016/j.scitotenv.2021.145413, 2021.