Most infectious diseases in humans start out in another animal. Three out of four new or emerging diseases in people come from animals, as well as six out of every 10 infectious diseases known to infect humans, according to the CDC.
The reason for this is simple: As we interact with our environment and all the living things in it, we’re bound to be exposed to zoonotic diseases—illnesses spread from animals to humans—whether we like it or not. Unfortunately, with climate change wreaking havoc on our planet, humanity’s chances of being exposed to new diseases are only likely to grow.
In a new study published Thursday in the journal Nature, researchers predict that climate change is going to shake up where animals live, abetting the exchange of more infectious viruses than ever before—and all in dangerous proximity to humans. Disconcertingly, this impending global health crisis may already be underway—and is likely to happen even if we manage to keep global warming down to 2 degrees Celsius, above which we would head into a world of unstable climate change.
ADVERTISEMENT
“This study takes an important first step at building a model to measure a hypothesis: That climate change will drive species to disperse as they track the climatic conditions that are most suitable,” Erin Mordecai, an infectious disease biologist at Stanford University, who was not involved in the study, told The Daily Beast in an email. “This dispersal will lead to novel contacts between species that have not before contacted each other in the wild, leading to the potential exchange of pathogens.”
For years, scientists studying climate change knew the storm surges, widespread flooding, and droughts brought on by a temperamental environment were the cause of waterborne illnesses and diarrheal diseases in vulnerable regions of the world, Dr. Aaron Bernstein, a pediatrician and public health researcher at Harvard T.H. Chan School of Public Health, who was not involved in the new study, told The Daily Beast.
“There’s some evidence that warming may be contributing to more malaria in places like the highlands of East Africa and the Andes in South America because mosquitoes are able to live higher on mountainsides,” Bernstein said. “But there has been, and continues to be, a lot of concern about how climate change might affect the movement of pathogens from one animal to another or from an animal to a person.”
We don’t have a clear picture of how thousands of mammal species seeking cooler climates will influence the global health landscape. There are about 10,000 viruses in nature that can infect humans that we know of. A majority of them are silently lurking in wild mammals and have a high probability of hopping over to humans, Thomas Gillespie, an ecologist and epidemiologist at Emory University, who was not involved in the study, told The Daily Beast.
To understand what the future holds, scientists at Georgetown University and other research institutions spent the last five years testing out different computer simulations, looking to see what would happen when land use and communities of a species changed alongside a changing climate. And what they found was startling: By the year 2070, there will be 4,000 times greater cross-species transmission of viruses. That means that wild mammals will share more viruses than ever before. On top of that, these hotspots of virus transmission are near human communities, particularly in tropical areas like Southeast Asia and East Africa.
“We [found] disproportionately these are settled areas that are full of people like lots of urban and underdeveloped areas will be experiencing these novel encounters that will have been driven by past climate change,” Gregory Albery, an infectious disease ecologist at Georgetown University and co-author of the new study, told reporters at a press conference Wednesday. “And it’s also happening in croplands more than expected compared to all these sorts of much wilder areas. These are obviously places that again, are in close proximity to humans and livestock.”
This forecast didn’t look at whether animal-to-human viral transmission skyrockets in tandem, but the researchers say it’s very likely we could see more outbreaks of familiar diseases like Ebola, influenza, and COVID-19, and outbreaks from new and unknown viruses.
“Climate change is creating innumerable hotspots of future zoonotic risk or present day zoonotic risk right in our backyard,” Colin Carlson, an environmental scientist at Georgetown University and co-author of the new study, told reporters at Wednesday’s press conference.
While the new study is a much needed wake up call, experts like Mordecai and Gillespie say more on-the-ground research needs to be done since the nature of infectious disease is complex and there are many factors—like human trade, mobility, and other animals like insects and birds—that tie in alongside climate change. But there’s hope this research will inspire humanity to get its act together in order to ward off the impending doom of climate change.
“[This paper] provides important motivation to reduce greenhouse gas emissions and mitigate climate change: It’s a pathway by which climate change may affect human and animal health,” said Mordecai. “Policymakers should also prioritize pathogen surveillance, particularly in settings where wildlife, humans, and livestock interact, as well as conservation of intact ecosystems that support healthy animal populations and ecosystem services.”
