When it comes to nature-based climate solutions, plants get all the love. It’s easy to envisage the carbon locked up in a mighty redwood or a forest of sea kelp. But now many scientists are also getting excited by the role that animals can play in sequestering carbon, through their diet and behavior, the way they cycle nutrients, and even how they die. This evolving science is called animating the carbon cycle. In 2019, the International Monetary Fund estimated that each great whale is worth well over $2 million in terms of the carbon it will sequester during its life. The science of such calculations is far from settled however, and even if it were, should we be valuing our planet’s other inhabitants according to how well they can clean up humanity’s carbon mess?
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The Power of The Herd
1 … In rivers. Humans are not the only ecosystem engineers. Water meadows behind the dams that beavers build collect wood and sediment containing carbon that can remain there for up to 600 years. In mature beaver habitats, the reservoirs they maintain can hold a quarter of the landscape’s soil carbon. Rewilding Colorado’s Rocky Mountain National Park with beavers could ultimately store an additional two million tons of carbon, say local geoscientists.
2 … On grasslands. At a larger scale, heavy grazers such as elephants and wildebeest can strip shrubs and small trees from the African savannah—and that’s not a bad thing. In 2009, researchers at the Imperial College in the UK calculated that grazers not only reduce combustible biomass, reducing the risk of wildfires, but also produce dung that returns nutrients and carbon to the soil.
3 … Deep at sea. But animating the carbon cycle really comes into its own on the open seas. If organic carbon can find its way to the deepest parts of the oceans, it becomes sediment and eventually rock—effectively permanent storage for humanity needs. Recent research by scientists from Rutgers University and elsewhere calculated that deep sea fish excreta and respiration stores 1.5 billion tons of carbon annually, worldwide. The bigger the animal, the more carbon saved. A fully restored global population of whales, sending their feces and (eventually) carbon-rich bodies to the ocean deep, might sequester over 1.5 billion tons of carbon every year, according to this excellent overview at Rewilding. Halting deep sea fishery altogether could potentially save hundreds of millions of tons more, say scientists at the University of Montpellier.
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Hold Your Horses
1. You can’t just add wildebeest to save more carbon. The same animal can be a carbon hero or a carbon villain in different situations. For example, a 2016 paper out of the University of California Santa Cruz found that wolves in North American forests might help carbon storage to the tune of nearly 100 million tons annually, by controlling tree-munching moose. On the other hand, the study noted that the same animals living on American grasslands prey on elk, which, like the wildebeest in Africa, have a net positive climate effect. Here, the wolves’ predation reduces carbon storage by 30 million tons a year. That makes it hard to design a wildlife program to reliably capture carbon over decades.
2. Ecosystems are moving targets. “We should be cautious in extrapolating carbon effects to whole ecosystems or landscapes when we look at only a subset of species,” says Monica Turner, an ecologist at the University of Wisconsin, Madison. writing in a comprehensive survey of wildlife carbon in PNAS. For example, grizzly bears and cougars also prey on elk, and there are many other grazing herbivores, too. Where, when, and how grazing and predation take place also affects how much carbon is stored—or emitted.
3. Wildlife is much more than carbon on the hoof. A recent paper calculated that all the world’s wild birds and mammals store carbon equivalent to perhaps eight minutes’ of fossil fuel use. But such a reductionist view is absurd. Protecting natural ecosystems and threatened species has benefits that extend far beyond carbon: biodiversity, agricultural resilience, extreme weather mitigation, and recreation. “When we think about a healthy ecosystem that’s got a vibrant mix of species and robust food chains, it doesn’t necessarily mean it’s always going to be the one that has the most carbon in it,” says Christopher Field, director of the Stanford Woods Institute for the Environment, in PNAS.
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What to Keep An Eye On
1. The return of predators. In some parts of the world, predator numbers have been bouncing back. In Europe, grey wolf numbers have increased by 1,800% since a low in the 1960s. Brown bears have increased 44%. The World Economic Forum thinks such rewilding can boost carbon uptake by between 1.5 and 12.5%. How those animals, and other species, co-exist with an expanding human population could determine the wider adoption of wildlife carbon strategies.
2. Innovative rewilding projects. Climate initiatives are increasingly linking conservation, wildlife, and carbon. Last month, for example, Jeff Bezos’s Earth Fund and the National Fish and Wildlife Foundation announced $30 million for two large scale projects spanning tens of millions of acres in the US, which explicitly connect wildlife conservation, ecosystem protection, and carbon sequestration. In Siberia, researchers have already re-introduced grazing horses to the tundra, to slow melting of the permafrost.
3. The money trees. With all the uncertainty over complex predator/prey processes, and given the urgency to pull down gigatons of carbon, most nations are focusing their resources on the certainties of vegetation. The 2021 IPCC Sixth Assessment recommended a range of nature-based climate solutions—focused on reforestation, plantations, agriculture management, and restoration of degraded coasts and peatlands, rather than wildlife strategies. As the science of animating the carbon cycle matures, that may change.
Top image: ©Anthropocene Magazine