Bison grazing in Yellowstone National Park

How Restoring Animal Populations Can Supercharge Carbon Absorption

By Jon Gorey, May 24, 2023


Forests are hardworking heroes in the fight to manage climate change, but they can’t remove enough carbon dioxide from the atmosphere to single-handedly help the world reach its Paris Agreement targets. However, what if we focus on protecting not just the trees, but also the larger animals that have historically lived among them, like gray wolves and elephants?

Well, that could get us a lot closer.

In a new study published in Nature Climate Change, an international team of researchers led by Yale ecology professor Oswald J. Schmitz found that protecting and restoring populations of animal species—including marine fish, gray wolves, wildebeests, sea otters, African forest elephants, and bison—can supercharge the carbon capture capabilities of their respective ecosystems, enhancing the total amount of CO2 naturally absorbed and stored by as much as 6.41 gigatons per year.

That’s more than 14 trillion pounds of CO2, and about 95 percent of the annual “negative emissions” needed to limit global warming to 1.5ºC in line with the Paris Climate Agreement.

The findings could have a big impact on land and marine conservation efforts, says Jim Levitt, director of the International Land Conservation Network (ILCN) at the Lincoln Institute. “This is not your everyday piece of natural climate solution research,” says Levitt, who was not involved in the study. “I think this is a major insight.”

Animating the Carbon Cycle

Climate change and a staggering worldwide loss of biodiversity are not just concurrent crises of the natural world; they’re two sides of the same coin, each impacting the other. This research suggests that the positive climate impacts of land and ocean conservation can be amplified even further when coupled with what’s called “trophic rewilding”—that is, protecting and restoring the functional roles of animals within their ecosystems.

That’s because many animals all over the world augment the carbon capture potential of their native habitats in different but impactful ways.

In the African Serengeti, for example, migrating wildebeests graze on grasses and, with the help of dung-burying insects, return that carbon to the soil. When disease decimated wildebeest populations in the early 20th century, the resulting overabundance of dry, uneaten grasses led to more frequent, intense wildfires that turned the savannah into a net emitter of CO2. Now the wildebeest population has recovered, and the Serengeti is once again a carbon sink.

Endangered forest elephants in central Africa, meanwhile, spread the seeds of trees and woody plants, and trample and devour vegetative undergrowth, helping carbon-dense overstory trees grow faster and bigger. Based on one of the authors’ earlier studies, the researchers estimate that restoring wild elephant populations just within the region’s 79 national parks and protected areas—about 537,000 square kilometers of tropical rainforest—could help capture roughly 13 megatons of additional CO2 per year, or 13 million metric tons.

Elephants at the Dzanga-Sanha reserve in the Central African Republic
African elephants at the Dzanga-Sangha Special Reserve in the Central African Republic. Elephant activity is essential to the health of the region’s carbon-dense rainforest. Credit: Andrey Gudkov via iStock/Getty Images Plus.

When large mammals like muskoxen trample arctic snowpack, that cold crust of compressed snow helps keep the soil below from thawing and releasing methane. Migrating marine fish eat algae near the surface and send it to the ocean floor as fecal pellets. Predators like sea otters help carbon-absorbent kelp forests thrive by keeping seaweed-munching sea urchins in check; gray wolves and sharks are responsible for similar “trophic cascades” in boreal forests and coral reefs, where they keep the populations of their smaller herbaceous prey in balance.

And in North America, where white settlers all but wiped out the more than 30 million bison that once roamed the prairies, just 2 percent of that animal’s one-time numbers remain, confined to about 1 percent of its historical range. Because grazing bison help grasslands retain carbon in the soil, restoring herds across even a small fraction of the landscape—less than 16 percent of a handful of prairies where human conflict would be minimal—could help those ecosystems store an additional 595 megatons of CO2 annually, the study found. That’s more than 10 percent of all the CO2 emitted by the United States in 2021.

“Using wild animal conservation explicitly to enhance carbon capture and storage is known as ‘animating the carbon cycle,’” the study’s authors write—and it demands a new way of thinking about conserved spaces as “dynamic landscapes.” It’s well understood that protecting nature as a climate solution can have the ancillary benefit of enhancing biodiversity, for example, but it turns out the relationship works both ways: Improving animal biodiversity can also enhance natural climate solutions. “It requires protecting and restoring the ability of animal species to reach ecologically meaningful densities so that as they move and interact with each other they can fulfill their functional roles across landscapes and seascapes.”

Failing to protect wildlife, meanwhile, can limit or even reverse an ecosystem’s carbon-storing potential. Overfishing of predatory fish in the coastal waters of the Northeastern United States, for example, led to an explosion of saltmarsh crabs, whose voracious appetite for seagrasses ravaged intertidal salt marshes, triggering their demise. Salt marshes are carbon supersinks that absorb and store up to 10 times as much carbon as a mature tropical rainforest. But when they die off, the resulting tidal erosion releases hundreds of years’ worth of stored sediment carbon, and a powerful carbon sponge disappears, along with all its future potential for CO2 capture.

Keeping Systems in Tune

For animal populations to recover their historical numbers and species diversity, they need large swaths of functionally intact ecosystems—which currently comprise just 2.8 percent of global land area. But “with the right enabling conditions, animal populations can rebound rapidly,” the authors write, with a measure of hope.

“If you give nature a chance to reestablish itself, it’s really, really efficient at doing so,” Levitt agrees, noting that many of the U.S. National Forests were once abandoned landscapes denuded of their timber. Now those swaths of forest are essential tools for absorbing atmospheric carbon. “Not only do the trees sequester carbon, but the soil, the animals, the insect life, and the mycorrhizal networks under the ground, they’re all sequestering carbon, and they all depend on a healthy chain of trophic networks,” Levitt says. “So there is utility, even related to the survival of our species, in having wild animals on open space. It’s not just beautiful, it keeps the carbon cycle in tune.”

As a resource hub connecting private and civic conservation groups across cultural and political boundaries, Levitt says ILCN has an important role to play in supporting the establishment of the types of linked, protected environments that promote greater biodiversity. “You really need large, interconnected, protected spaces to get to truly rich ecosystems,” he says. “And what networks can do is make land conservation contagious sociologically—meaning, if your next-door neighbor has conserved his property, you’re more likely to do the same thing.” ILCN also supports the global 30×30 effort, an agreement among more than 190 countries to work toward protecting 30 percent of the world’s land and oceans by 2030.

Expanding the range of intact ecosystems to restore and protect animal populations will require people and wildlife to share space in more dynamic “coexistence landscapes,” the authors add. “This involves seeking ways for wild animals and humans to coexist across landscapes and seascapes, rather than separating people from nature, as has been a common practice in proposals to apportion spaces for biodiversity and carbon storage.”

While the study’s authors acknowledge the challenge of such a cultural shift, they also note, with some urgency, that the opportunity is too great to squander. “We are losing populations of many animal species just as we are discovering how much they functionally impact carbon capture and storage.”


Sea otter in waters off Alaska
Sea otters, which are listed as threatened under the Endangered Species Act, help carbon-absorbing kelp forests thrive by keeping sea urchin populations in check. Credit: roclwyr via iStock/Getty Images Plus.



Jon Gorey is a staff writer for the Lincoln Institute of Land Policy.

Lead image: Bison grazing in Yellowstone National Park. Credit: panugans via iStock/Getty Images Plus.