When people warn that the destruction of nature is contributing to climate change, the image that often comes to mind is tropical rainforests felled by chainsaws and fires. Oswald Schmitz would like you to think about something else as well: wildebeests.
When people talk about both the causes and solutions for the climate crisis plants are often the centerpiece of conversations when it comes to natural systems. It makes sense that people would think of plants first, since they suck CO2 out of the air and turn it into wood and greenery.
For years, Schmitz, a Yale University ecologist, has worked to draw people’s attention to the under-appreciated ways in which animals are also part of the carbon equation. A decade ago he helped coin the term “animating the carbon cycle” to draw attention to this.
Now, writing in Nature Climate Change, he lays out the case that returning wild animals to their native habitats—known as “rewilding”—can also make a sizeable dent in our carbon surplus.
“Wildlife species, throughout their interaction with the environment, are the missing link between biodiversity and climate,” said Schmitz, who wrote the new paper with fellow scientists from the U.S., Canada, Europe and South Africa.
Take the wildebeest or gnu. With its boxy head, upturned horns and slender hindquarters, it resembles a bison on a diet. More than a million of the creatures traverse the African savannah today, turning grass into gnu poop as they go. But early in the 20th century, things were much more dire. Their numbers plunged to 300,000 due to a disease introduced by domestic cattle. As the migrating herds dwindled, grass grew unchecked, fueling bigger wildfires, which sent more carbon into the atmosphere along with the smoke.
As a consequence, the Serengeti, scientists estimate, switched from a carbon sink—absorbing more carbon than it emitted—to a carbon source. Today, with the disease eradicated and wildebeest herds back, these grasslands are once again a carbon sponge, storing up to 4.4 million tons more CO2 than when wildebeest numbers were at their lowest.
To make their case, Schmitz and his co-authors went beyond a single example. They set out to quantify just how much more carbon could be taken up by ecosystems if major animal populations were protected or revived. Their total number: An eye-popping 6.4 billion tons of CO2 every year. That’s roughly a sixth of global energy-related emissions in 2021.
The number comes from scientists’ estimates for the climate impacts of a variety of large, ecosystem-shaping organisms. There are sea otters, muskox, bison, wolves, and wildebeests, among others. These creatures can alter carbon dynamics in a variety of ways. In past stories, I’ve touched on a few. African forest elephants, for instance, are credited with boosting carbon stores as they feast on trees, making room for carbon-rich species and spreading seeds in their dung. Baleen whales have been touted as climate warriors because the iron concentrated in their feces triggers carbon-absorbing phytoplankton blooms.
But the effects of these giant whales—and the other species they examined—are dwarfed by schools of smaller ocean-going fish. Boosting whale numbers in the Southern Ocean could capture 620,000 tons of CO2, while fish around the world capture as much as 5.5 billion tons, according to one estimate.
These numbers are an incomplete picture. Due to a lack of data, the scientists didn’t include a number of species that could be players in an ecosystem’s carbon dynamics: African buffalo, white rhinos, pumas, apes and monkeys, fruit bats and others.
Still, for Schmitz, the message is clear. “Allowing key animal species to reach ecologically meaningful densities as part of dynamic landscapes and seascapes would probably shorten the time” it takes to hit milestones for reducing atmospheric carbon.
Which raises a question. With everyone from fossil fuel giants to global superpowers to local do-gooders pledging to plant trees to help capture carbon, is anybody going to start a similar campaign to, say, release more wolves in the name of protecting the climate?
Schmitz, et. al. “Trophic rewilding can expand natural climate solutions.” Nature Climate Change. March 27, 2023.
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