Why helping whales to flourish can help fight climate change

The ocean is one of the planet’s major carbon sinks, absorbing almost a third of the atmosphere’s greenhouse gas emissions.

In its depths swim the great cetaceans, a population whose sheer physical mass allows them to exert an outsized impact on the ecosystem around them. While researchers have long suspected that whales play a key role in the ocean’s carbon cycle, it has proven difficult to quantify exactly how these animals are transforming the oceans – and what we lost by depleting them a century ago.

Now a group of scientists has taken up this challenge. A team of ecologists, biologists and oceanographers recently published one of the most comprehensive efforts to understand how much carbon the great cetaceans are absorbing from the ocean and what value this has in the fight against climate change.

Whales are “big animals, they live long lives, many of them migrate long distances,” said study leader Heidi Pearson, a marine biologist at the University of Alaska Southeast. “And so they have the potential to have these huge ecosystem impacts, including the carbon cycle.”

At their most direct impact, whale bodies contain an enormous amount of carbon that would otherwise be in the ocean or atmosphere.

Twelve large whale species — minke whales, Antarctic minke whales, sei whales, Bryde’s whales, blue whales, fin whales, bowhead whales, gray whales, humpback whales and three species of right whales — hold an estimated 2 million tons of carbon in their bodies, the authors found. That’s roughly equivalent to the amount of carbon released by burning 225 million gallons of gasoline.

And that’s just the living members of the whale family. Another 62,000 tons of carbon — the equivalent of 7 million gallons of gas — are trapped each year in the form of whale falls, the bodies of dead whales that sink to the sea floor and support a scavenger ecosystem.

“Whale falls are a very good way, in terms of efficiency, to take carbon from the upper ocean and take it to the deep sea for sequestration,” said Craig Smith, an oceanographer at the University of Hawaii at Manoa who worked on the study.

When a whale dies in open water and sinks to the depths, a lifetime of accumulated carbon is associated with it. It can take up to 1,000 years for water and seafloor elements to return to the surface, meaning carbon is effectively sequestered for the better part of a millennium.

Additionally, whales indirectly affect the ocean carbon cycle through a less majestic but vitally important by-product: their droppings.

Walker feces are rich in fertilizing elements such as nitrogen, phosphorus and iron, which are critical for phytoplankton growth. These nutrients are found in relatively small amounts in the surface waters of the oceans.

But when whales defecate near the ocean’s surface, their waste fertilizes the growth of organisms at the base of the marine food chain and enhances the growth of carbon-consuming life throughout the ecosystem. In the Southern Ocean alone, this process fixes an estimated 22 million tons of carbon in a web of living animals, the study’s authors calculated.

The research results were published in December in the journal Trends in Ecology and Evolution.

Great whales circulate nutrients and carbon through their ecosystem in both direct and indirect ways.

(Trends in Ecology & Evolution / Pearson)

The paper is “an excellent summary of the progress that has been made over the past decade” to quantify whales’ role in the carbon cycle, said Michael J. Moore, a senior scientist and veterinarian at the Woods Hole Oceanographic Institution who was not involved was with work.

It’s “a wonderful thought experiment with oceans of the unknown,” he said, many of which credit the authors in the paper.

For one, the researchers couldn’t quantify how much carbon whales breathe back into the atmosphere through respiration, Pearson said.

Whales are also quite literally a slippery population, and the impact of whale droppings in particular is difficult to determine. However, their research together shows that the more whales there are, the healthier the ocean.

“The recovery of whales,” the study authors conclude, “could be an effective ‘low-regret’ CDR [carbon dioxide removal] Strategy with less risk, longer durability and higher efficiency than geoengineering solutions.”

Whale populations have still not recovered from the devastating effects of industrial whaling. Commercial hunting in the 19th and 20th centuries reduced the total mass of whales on the planet by 81%, and ultimately released 17 million tons of carbon into the atmosphere that was previously stored in the bodies of baleen whales, according to the authors.

Rebuilding whale populations alone is not enough to heal the oceans. Global fossil fuel consumption released 37.5 billion tons of carbon dioxide in 2022, the highest level ever recorded in a single year. That’s more than 18,000 times the amount of carbon contained in all large cetaceans alive today.

Whales alone “won’t solve climate change, but thinking about whales playing a role in the carbon cycle can help motivate conservation,” said Andrew Pershing, study co-author and director of climate science at the nonprofit Climate Central. “There’s a lot of win-win situations there, and I think that applies to a lot of natural climate solutions.”