Over the next 50 years, climate change could lead to more than 15,000 new cases of mammals transmitting viruses to other mammals, according to a study published in Natureone. He is one of the first to predict how global warming will change wildlife habitats and increase encounters between species capable of exchanging pathogens, and to quantify how many times viruses are expected to jump between species.
Many researchers say the COVID-19 pandemic likely began when a previously unknown coronavirus jumped from a wild animal to a human — a process called zoonotic transmission. A projected rise in species-hopping viruses could trigger further outbreaks, posing a serious threat to human and animal health alike, the study warns, providing yet another reason for governments and health organizations to invest in pathogen surveillance and improve health care infrastructure. .
The study is “a critical first step in understanding the future risk of climate and land-use change in the next pandemic,” says Kate Jones, who models interactions between ecosystems and human health at University College London.
The research predicts that much of the transmission of the new virus will occur when the species first encounter each other as they move to cooler locations due to rising temperatures. And he projects that this will occur more frequently in species-rich ecosystems at high elevations, particularly in areas of Africa and Asia, and in areas densely populated by humans, including the African Sahel region, India and Indonesia. Assuming the planet warms by no more than 2°C above pre-industrial temperatures this century, a future predicted by some climate analyses, the number of first-time encounters between species will double by 2070, creating transmission hotspots for viruses, the study says.
“This work gives us more incontrovertible evidence that the coming decades will not only be hotter, but sicker,” says Gregory Albery, a disease ecologist at Georgetown University in Washington DC and a co-author of the study.
The challenges of modeling
To make their predictions, Albery and his colleagues developed and tested models and ran simulations over a five-year period. They combined models of virus transmission and species distribution under various climate change scenarios, focusing on mammals due to their relevance to human health.
The team built the species distribution model to predict where mammals would move to find more habitable habitats as the planet warms. The virus transmission model predicts the probability that a virus will jump between species for the first time, taking into account where species might be found as their habitats change and how closely related they are evolutionarily (viruses are more likely to be transmitted between related species).
The model appears “technically flawless,” says Ignacio Morales-Castilla, a global change ecologist at the University of Alcalá, Spain, although he points out that forecasting exercises like this sometimes need to include unrealistic assumptions. But he adds that the breadth and scope of the research and its ability to identify which parts of the world might be most at risk “stand out clearly.”
One assumption the researchers had to make was about how far and wide species would spread as the climate changes. But factors like whether mammals can adapt to local conditions or cross physical barriers in landscapes are hard to predict.
Bats are projected to be involved in viral transmission regardless of these factors, the study found. Bats are believed to be part of the origins of COVID-19 and are known reservoirs of the virus, constituting around 20% of mammals. The team says that, in part because bats can fly, they are less likely to experience barriers to changing their habitats.
Overflows to humans?
Although Jones applauds the study, he urges caution in discussing its implications for human health. “Predicting the risk of viral jumps from mammals to humans is more complicated, as these secondary effects take place in a complex ecological and human socioeconomic setting,” she says.
Many factors could reduce the risk to human health, including increased investment in health care or a virus not being able to infect humans for some reason, it adds.
But the researchers insist that there is no time to waste. The Earth has already warmed more than 1°C above pre-industrial temperatures, and this is driving species migration and disease sharing. “It’s happening and it can’t be prevented, even under the best of climate change scenarios,” says Albery.
Albery and one of his co-authors, Colin Carlson, a global change biologist also at Georgetown University, say that while some increase in disease transmission is inevitable, that’s no excuse for inaction. The researchers call on governments and the international community to improve monitoring and surveillance of wildlife and zoonotic diseases, particularly in future hotspots such as Southeast Asia. Improving health infrastructure is also essential, they say.
As people begin to prepare for and adapt to global warming, most efforts are focused on activities like stopping deforestation or reinforcing levees. But Carlson says that pandemic preparedness and disease surveillance are also an adaptation to climate change.