Why COVID-19 Demands Action on Climate Change

Dr. Kevin Njabo and Dr. Smith (right) doing research on birds in the rainforests of Cameroon.

As a scientist I study the ecology of disease. COVID-19 has shown the world the horrors of a pandemic. Climate change is an accelerator for pandemics. It’s time to wake up and take action -- our future depends on it.

Smith and colleague collect samples from poultry in a village in Uganda.

Before discussing pandemics and climate change let’s review some facts. For the past three months human life on the planet has been turned upside down by a tiny virus. The origin of the pandemic was most likely a spillover event from a wild bat to a human -- possibly aided by an intermediate animal host. For those of us who study disease, periodic pandemics are no surprise. They are simply a feature of human history and will reoccur in the future, even as we try to minimize their impact. Epidemiologists know that three out of every four infectious human diseases come from animals. The list of diseases that arose via spillovers tell a tragic story of human suffering: AIDs, Ebola, Yellow Fever, and now COVID-19. While the frequency of pandemics varies throughout history, the last major pandemic occurred a little more than 100 years ago, when the 1918 Spanish flu spilled over from birds to humans and killed upwards of 40 million people worldwide.

"Climate change is an accelerator for pandemics. It’s time to wake up and take action -- our future depends on it.”

In recent decades biologists have become increasingly concerned that the likelihood of spillover events may be increasing. This belief is based on the fact that as humans expand further and further into pristine habitats, they come closer into contact with wild animal species and their pathogens. For example, Tropical rainforests (where I work) cover only 7% of the land area of Earth, but harbor more than 50% of the species. With this incredible diversity of species comes a diversity of disease-causing organisms, most of which co-evolved with their hosts over millennia. Spillover events typically occur when you perturb a natural ecosystem where a host and its pathogens have co-evolved. Human activities such as building a road into a pristine rainforest or cutting down a patch of forest can expose humans to these pathogens. Another way is when wild animals are removed from their natural habitats and sold in wildlife markets for their flesh. Wildlife markets, common in many parts of Asia, Africa and South America, provide ideal mixing vessels for pathogens, allowing them to spillover into intermediate hosts such as domestic poultry or swine, or other captive wild animals, before infecting humans.

Rainforest, Dja Reserve Cameroon.

The dynamics of spillover events are often described as “viral chatter,” where the intensity and frequency of the chatter rises and falls depending on various circumstances and the proximity of wild animals, their pathogens and humans. Only on rare occasions, like the one we are currently in, are the conditions just right for a disease to take off and become a pandemic.

"Could climate warming increase viral chatter? Yes. As animal and human populations move in response to climate warming, new pathogens and animals will come into contact intensifying viral chatter.”

Could climate warming increase viral chatter? Yes. As animal and human populations move in response to climate warming, new pathogens and animals will come into contact intensifying viral chatter. It's estimated that some animals will need to move to higher latitudes, traveling hundreds, even thousands of miles to reach cooler climates, while other species will move up to higher elevation. Research tells us that many species unable to make these journeys are destined to contribute to a possible 6th mass extinction. For those species that survive, their new, future ecosystems will likely be radically different, providing many opportunities for hosts and their pathogens to reassort themselves in novel ways. With climate warming human populations will also move, coming into contact with new constellations of species and their pathogens. Numbers of human climate refugees will also dramatically rise, with refugee camps serving as ideal incubators for developing pandemics.

White-bellied pangolin taken in Central Africa Republic (photo by R. Rosomoff).

It’s reasonable to assume that rates of viral chatter and disease spillover events will increase under climate change and lead to new pandemics. Imagine if a spillover event of a pathogen such as Nipha virus, with a human fatality rate of 40 percent, coincided with mass migrations, a climate refugee crisis and civil unrest. This is a recipe for a disastrous, raging pandemic. What would our world be like if the frequency of pandemics shifted to every five-to-ten years instead of every hundred? Society as we know it might well cease to exist. There is only one way to prevent such a grim calamity: we must work quickly to lower greenhouse gas emissions to reduce climate warming and preserve biodiversity. Ultimately this will limit “viral chatter” for a safer, healthier world.

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