With new variants of the novel coronavirus popping up across the world, a recent study has shed light on the origins of SARS-CoV-2, pointing to climate change as a potential driver of its emergence.
The study, published in the journal Science of the Total Environment, offers the first lines of evidence for how climate change could have played a direct role in the appearance of the COVID-19 pandemic-causing virus. The research also highlights the potential mechanism involved in the phenomenon.
Researchers on the study discovered that over the last century, large-scale changes in the kind of vegetation present in the Yunnan province in Southern China, as well as neighboring regions in Myanmar and Laos, contributed to altered climactic conditions leading to changes in the bat populations in the region.
This area is the source of an estimated 100 bat-borne coronaviruses, of which some are ancestors of SARS-CoV-1 and SARS-CoV-2. The study found that climate change may have played a key role in the evolution or transmission of these two SARS coronaviruses in particular.
The study found that climate changes in the region included increases in temperature, sunlight and atmospheric carbon dioxide, all of which impact the growth of plants and trees. This has led to changes in natural habitats, with the conversion of tropical shrubland to tropical savannah and deciduous woodland. And in turn, these alterations gave rise to a suitable environment for many bat species that live in the forests.
The number of coronaviruses in a region is correlated to bat species richness — the number of different species of bats. The richness is likely to have led to the origin of SARS-CoV-1 and 2, and climate change may have been a key factor in the outbreaks of the two viruses.
According to the study, “Species richness is affected by climate change, which drives the geographic distributions of species by altering the suitability of ecological habitats, forcing species to disappear from some areas whilst allowing them to expand in others.”
These shifts not only affect the spatial distribution of species, but also their composition and the ecology of a given area. All of this can lead to changes in the distribution of zoonoses across host species, resulting in potentially novel host-pathogen interactions that could introduce selection pressures to foster the evolution of harmful variants and new transmission pathways.
Changes in the global distribution and composition of bat species as they relate to changes in climate is important to understand in the context of the emergence of novel coronaviruses that can cause disease outbreaks in humans through zoonotic transmission.
The study found that over the last hundred years, about 40 bat species moved into the Yunnan province. This has contributed to the 100 different types of bat-borne coronavirus that are currently present in the region. Genetic lineage tracing has revealed that SARS-CoV-2 likely arose in this “global hotspot.”
This hotspot of increased bat diversity is also home to pangolins, which have been seen as the probable intermediate hosts that gave rise to the evolution of the human-infecting SARS-CoV-2. The likely occurrence of a SARS coronavirus jumping from bats to pangolins was traced to an illegal wildlife market in Wuhan, Yunnan where the animals were sold and where the first human outbreak of the respiratory infection occurred.
The research revealed that changes in climate conditions led to shifts in bat diversity and distribution not only in China and surrounding regions, but at the global scale.
Comparative Analysis and Mapping
For the study, researchers generated a map of the world’s vegetation as it was 100 years ago using recorded data of temperature, precipitation and cloud cover back then. They then worked out the global distribution of the different bat species in the early 1900s using information about the vegetation in habitats where bats thrive. They compared their constructed map to current vegetation and bat distributions to evaluate “species richness” and how it has changed over time with climate change.
Dr. Robert Beyer, a researcher in the University of Cambridge’s Department of Zoology and first author on the study, commented, “Climate change over the last century has made the habitat in the southern Chinese Yunnan province suitable for more bat species,” He added that, “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.”
Over 60 percent of emerging infectious disease events worldwide have zoonotic origins, with the majority originating in wildlife.
Bats are a prime pathogen host as they carry the highest proportion of zoonotic viruses of all mammals, harboring over 3,000 different coronaviruses across all the different bat species worldwide. On average, each bat carries 2.7 different coronaviruses. Given the high viral load, viruses account for over a third of the bat virome, which has led to the current estimates of the number of coronaviruses that they carry.
Climate Change as a Driver of Disease Outbreaks
While the viruses don’t produce any symptoms in bats, with changes in climate leading to shifts in vegetation that impact the evolution and transmission of the pathogens, this could very well change with the emergence of novel strains. And importantly, changes in climate can drive the surfacing of new coronavirus strains and variants that can infect humans, as the current pandemic has shown us quite clearly.
The study also showed that over the last century, climate change has led to increases in bat populations around the world, including regions around Central Africa and some areas in Central and South America.
The study researchers warn about the role of climate change in viral disease outbreaks and put emphasis on the importance of addressing climate change as part of COVID-19 economic recovery programs.
“The COVID-19 pandemic has caused tremendous social and economic damage. Governments must seize the opportunity to reduce health risks from infectious diseases by taking decisive action to mitigate climate change,” said Professor Andrea Manica in the University of Cambridge’s Department of Zoology, who was involved in the study.
“The fact that climate change can accelerate the transmission of wildlife pathogens to humans should be an urgent wake-up call to reduce global emissions,” commented Professor Camilo Mora at the University of Hawai’i at Manoa, who initiated the project.
In light of this, the researchers stressed the importance of limiting the expansion of urban areas, farmland and hunting grounds into natural habitat to reduce contact between humans and disease-carrying animals.
The research highlights the close links between climate change and fluctuations in global biodiversity, underscoring the significance of realizing the interconnectivity between earth’s processes.