Climate change is frequently described as a threat multiplier, something that exacerbates existing problems and creates new ones. No aspect of life on this planet has been untouched by climate change — viruses included.
The world is rife with viruses; at least 320,000 kinds are known to infect mammals alone. And these pathogens rarely stick within one species.
Most of the pandemics of the past 100 years — indeed, most of the diseases that humans can have — were caused by “zoonoses,” or germs that come from other animals. HIV emerged from nonhuman primates. Ebola is borne by bats. The measles virus evolved from a disease that hurts cows sometime around the third century A.D.
Viruses hijack the cellular machinery of their hosts to make copies of themselves, and many don’t have any proofreading mechanism to edit mistakes out of their genetic material. This means they mutate far faster than cellular life and can adapt to change rapidly.
By altering the environment at a faster rate than any other moment in geologic history, scientists say, humans have created a wealth of chances for viruses to evolve.
Habitat fragmentation is a major problem, said Dave O’Connor, a virologist at the University of Wisconsin at Madison. Human incursions into animal habitats — chopping down forests to build farms, venturing into parks to poach — bring us into increasing contact with animals and make us more likely to pick up their diseases. The shortage of places where animals can live also brings them into increasing contact with one another.
“You have these complex networks of interactions that you wouldn’t be seeing under less disturbed circumstances,” O’Connor said. “And that provides a lot of opportunities for these diseases to explore alternate hosts and acquire some of the features that would be necessary to make them” jump species.
Climate change compounds these problems, researchers say. It shrinks some animal populations, depriving them of the genetic diversity needed to control disease. It forces others to migrate, producing new kinds of animal-to-animal and animal-to-human interactions. Studies have linked outbreaks of several zoonotic diseases to extreme weather events such as droughts and floods that are expected to become more common as the planet warms.
To make matters worse, a warmer planet is expected to be a less stable one. More people will be displaced by natural disasters. Droughts and the resulting food shortages could trigger political conflict. Societies ravaged by wars and humanitarian crises are less able to maintain the infrastructure needed to preserve public health. The loss of clean water, access to health care and disease surveillance from government agencies can make it easier for pathogens to spread.
A Harvard University study of those sickened in the covid-19 pandemic also showed that people living in polluted environments are far less able to fight off the disease — an issue that will become even more prominent as the planet warms. The nation’s leading climate scientists have said that higher temperatures will lead to increasing concentrations of allergens, ozone and small particles that irritate the lungs.
Thomas Friedrich, a colleague of O’Connor’s who spent much of his time studying the Zika virus (which is borne by mosquitoes) before SARS-CoV-2 overwhelmed the world, said people often ask him why humans can’t simply eliminate the sources of our zoonoses.
That’s a dangerous way of thinking, he said. Aside from the impossibility of killing off entire species, these creatures play a vital role in their ecosystems. Bats, for example, participate in pollination and eat mosquitoes and agricultural pests. Even if killing them could avert the next coronavirus (which it can’t), it would hurt humanity — and the world — in myriad other ways.
“The answer isn’t to just find the smoking gun that we can point and shoot,” Friedrich said. “The health of the animal-human interface is what’s important.”
This is perhaps the strongest link between the coronavirus and climate change, said Elena Bennett, an ecosystem ecologist at McGill University in Montreal and a co-founder of the group Seeds of Good Anthropocenes, which collects and studies climate solutions. Both crises underscore that humans cannot be healthy unless the planet is, too. Both demand that people do what had been previously unimaginable, whether it’s shutting down society or transforming it.
“I’m an optimist by nature,” Bennett said — someone who looks for bright spots when other people see only dark.
In this time of uncertainty and loss, she is heartened by the speed with which humans have responded to the coronavirus. And she thinks the tools people have developed to deal with the pandemic may be helpful in confronting climate change.
The mutual aid efforts that have sprung up to get groceries or create masks for vulnerable people show the potential for community action, Bennett said. The call for people to stay home — and the measurable impact of social distancing efforts when people comply — reveals the importance of official actions and the need for every person to participate.
“The power of one person to do good or bad is kind of amazing, and that power happens because of all the interactions in the system,” Bennett said.
In the months and years to come, when a covid-19 vaccine is developed and the pandemic is contained, she hopes people won’t forget these bright spots. “How do we take these good things and hold onto them,” she asked, “and steer them toward the larger climate conversation?”