Climate Change Is Rewiring the Network of Animal Viruses - The Atlantic
▻https://www.theatlantic.com/science/archive/2022/04/how-climate-change-impacts-pandemics/629699
For the world’s viruses, this is a time of unprecedented opportunity. An estimated 40,000 viruses lurk in the bodies of mammals, of which a quarter could conceivably infect humans. Most do not, because they have few chances to leap into our bodies. But those chances are growing. Earth’s changing climate is forcing animals to relocate to new habitats, in a bid to track their preferred environmental conditions. Species that have never coexisted will become neighbors, creating thousands of infectious meet-cutes in which viruses can spill over into unfamiliar hosts—and, eventually, into us. Many scientists have argued that climate change will make pandemics more likely, but a groundbreaking new analysis shows that this worrying future is already here, and will be difficult to address. The planetary network of viruses and wildlife “is rewiring itself right now,” Colin Carlson, a global-change biologist at Georgetown University, told me. And “while we thought we understood the rules of the game, again and again, reality sat us down and taught us: That’s not how biology works.”
In 2019, Carlson and his colleague Greg Albery began creating a massive simulation that maps the past, present, and future ranges of 3,100 mammal species, and predicts the likelihood of viral spillovers if those ranges overlap. The simulation strained a lot of computing power; “every time we turn it on, an angel dies,” Carlson told me. And the results, which have finally been published today, are disturbing. Even under the most optimistic climate scenarios, the coming decades will see roughly 300,000 first encounters between species that normally don’t interact, leading to about 15,000 spillovers wherein viruses enter naive hosts.
The Anthropocene, an era defined by humanity’s power over Earth, is also an era defined by viruses’ power over us—a Pandemicene. “The moment to stop climate change from increasing viral transmission was 15 years ago,” Carlson said. “We’re in a world that’s 1.2 degrees warmer [than preindustrial levels], and there is no backpedaling. We have to prepare for more pandemics because of it.”
Southeast Asia will also be especially spillover-prone because it’s home to a wide range of bats. Flight gives bats flexibility, allowing them to react to changing climates more quickly than other mammals, and to carry their viruses farther. And bats in Southeast Asia are highly diverse, and tend to have small ranges that don’t overlap. “You shake that like a snowglobe and you get a lot of first encounters,” Carlson said.
Such events will also be problematic elsewhere in the world. In Africa, bats are probably the natural reservoirs for Ebola. Thirteen species could potentially carry the virus, and as global warming forces them to disperse, they’ll encounter almost 3,700 new mammal species, leading to almost 100 spillovers. So far, the biggest Ebola outbreaks have occurred in West Africa, but Carlson said that within decades, the disease could easily become a bigger problem for the continent’s eastern side too. “And that’s emblematic of everything,” he told me: Every animal-borne disease will likely change in similarly dramatic ways.
And spillovers that initially occur between other mammals could someday affect us: The original SARS virus hopped from bats to humans via civets, and HIV reached us from monkeys via chimpanzees and gorillas. For an animal virus to jump into humans, geography, biological compatibility, and other factors must line up in just the right way. Each event is unlikely: Imagine playing Russian roulette using a gun with a million chambers. But as the climate changes, we’re loading more of those chambers with bullets, and pulling the trigger more frequently.
The revelations are “so large and heavy to behold that even as we were writing them, we didn’t want to,” Carlson said. But despite every attempt that he and Albery made to naysay their own work, the simulation kept spitting out the same results. They confirm that three of our greatest existential threats—climate change, pandemics, and the sixth mass extinction of wildlife—are really intertwined parts of the same mega-problem. To tackle it, “we need atmospheric scientists talking to ecologists talking to microbiologists talking to demographers,” Rachel Baker, whose research at Princeton focuses on climate and disease, told me.
But pandemics are inherently unpredictable, and no amount of prevention will fully negate their risk. The world must be ready to meet the viruses that slip through the net. That means fortifying public health and health-care systems, strengthening social safety nets, and addressing all the weaknesses of the pre-COVID normal that made the world so vulnerable to the current pandemic and will leave it susceptible to the next. The world, in its desire to move past COVID, is already forgetting the lessons of the recent past, and perhaps assuming that a generation-defining crisis will occur only once a generation. “But no, all of this could happen again tomorrow,” Carlson said. And “if this many viruses are undergoing host jumps this much,” multiple pandemics could strike together.