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The reasons for this new era of pandemics are complex, but as Fauci and Morens point out, one of the main drivers is the climate crisis, which is shaking up the natural world and rewriting disease algorithms on the planet. Thawing permafrost in the Arctic is releasing pathogens that haven t seen daylight for tens of thousands of years. The Vibrio bacteria that causes cholera, a diarrheal disease that haunted big cities like London and New York in the 19th century and still kills tens of thousands each year, thrives in warmer water. An even more deadly strain of the same bacteria, Vibrio vulnificus, while rare, has been detected more and more frequently in bays and estuaries on the East Coast, particularly around Chesapeake Bay. Vibrio vulnificus, if you happen to eat shellfish, might give you a bad stomachache (in rare cases, it can be fatal). If the bacteria gets in a cut or wound, however, it becomes a flesh-eating horror and kills one in five people who come in contact with it.
But the biggest impact may be on the emergence of new pathogens from animals. Through intensive agriculture, habitat destruction, and rising temperatures, we are forcing creatures to live by the cardinal rule of the climate crisis: adapt or die. For many animals, that means migrating to more hospitable environments. In one recent study that tracked the movement of 4,000 species over the past few decades, as many as 70 percent had moved, almost all of them seeking cooler lands and waters. Some animals have made big leaps. Atlantic cod have moved more than 120 miles per decade. In the Andes Mountains in South America, frogs and fungi species have climbed a quarter mile higher over the past 70 years. In Alaska, hunters are discovering parasites from more than 950 miles southeast in Canada, alive under the skin of wild birds (tiny parasites adapt better to rapidly changing temperatures than large animals). Great white sharks are turning up as far north as Maine. A wild exodus has begun, writes Sonia Shah in The Next Great Migration. It is happening on every continent and in every ocean.
During this wild exodus, these animals are likely to bump into new animals and humans they have never crossed paths with before. Carlson, the Georgetown biologist, calls these events meet cutes random encounters where viruses jump species and new diseases are often born. The vast majority of the new infectious diseases that have emerged in recent decades have come from these zoonotic pathogens, as they are called, with bats, mosquitoes, and ticks being among the most competent carriers of new viruses. When they jump to humans, we get pandemics like Covid-19. What s next? It s really a roll of the dice, says Raina Plowright, an epidemiologist at Montana State University who studies the emergence of new diseases. By one count, an estimated 1.7 million currently undiscovered viruses are thought to exist in mammal and avian hosts. Of these, more than 800,000 could have the ability to infect humans.
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