Some of the most awe-inspiring animals on Earth, whales have loomed large in culture and as a symbol of natural conservation.

Still, these giant creatures face a number of threats, from ship collisions and noise pollution, to commercial whaling. Japan is one of the few countries to still hunt the animals commercially, with minke whaling for the year commencing last week.

But beyond concerns over the impact of reduced whale populations on marine ecosystems, there’s now increased attention being paid to the role they have in helping the fight against climate change.

That all comes down to how they can help keep carbon dioxide out of the atmosphere in both direct and indirect ways.

Carbon is found in all living things, but because of their size and long life spans the amount is much more significant in the case of whales. At the top end of longevity, bowheads — weighing up to 91 tons and measuring as long as 19 meters — can live for over 200 years, scientists estimate.

When they die, whales typically take the carbon in their body to the deep ocean through “whale falls,” which see their bodies come to rest on the seafloor thousands of meters down. There, the carbon will be kept — “sequestered” in the technical terminology — for potentially thousands of years.

According to calculations in a December paper in Trends in Ecology and Evolution, whale falls currently lead to the sequestration of 62,000 tons of carbon per year — equivalent to around 2.8 million trees. For the pre-whaling population, it was much higher, at 360,000 tons. Still, even that would not make a significant dent in reducing carbon in the atmosphere.

“The kicker with the direct pathways — those that we understand the best as of right now — is that in the grand scheme of things, it's not a whole lot of carbon,” says Heidi Pearson, associate professor of marine biology at the University of Alaska Southeast and the lead author of the Trends in Ecology and Evolution paper.

Children watch a Baird's Beaked whale being dragged to be butchered at Wada port in Minamiboso, Chiba Prefecture, in July 2019. Whales face a number of threats, from ship collisions and noise pollution to commercial whaling. | REUTERS
Children watch a Baird's Beaked whale being dragged to be butchered at Wada port in Minamiboso, Chiba Prefecture, in July 2019. Whales face a number of threats, from ship collisions and noise pollution to commercial whaling. | REUTERS

A more promising way that whales keep carbon out of the atmosphere comes through the indirect way they contribute to carbon sequestration, which stems from their role in stimulating the growth of phytoplankton — microscopic marine algae that, among other things, turn inorganic carbon in the atmosphere into organic compounds, with some of this carbon exported to the deep sea.

Whales do this in two ways. Firstly, by moving nutrients upward through the water column to near the surface via feces and other byproducts, which stimulate the growth of phytoplankton. And secondly, through the “great whale conveyor belt,” which sees whales move from nutrient-rich feeding grounds to nutrient-poor breeding areas, thereby stimulating phytoplankton production.

That role in carbon sequestration and phytoplankton growth, combined with whales’ value in terms of their contribution to the marine food chain and tourism, has drawn the attention of the International Monetary Fund, with a paper led by Assistant Director Ralph Chami putting the average value of a whale at $2 million (about ¥265 million). That in turn has raised the prospect of financial incentives to maintain and rebuild whale populations, with resulting credits potentially used to offset emissions.

But the Trends in Ecology and Evolution paper pushed back against the ideas presented by Chami and others, arguing that there currently isn’t the scientific certainty to attribute such a high level of carbon sequestration to whales. In particular, they pointed to such issues as regional variation in the amount of carbon exported to the deep ocean by phytoplankton and zooplankton, as well as a lack of data for the theorized increase in phytoplankton’s production of organic material.

“There is still much we need to learn about every single step in that pathway, and that's where the uncertainty comes from,” says Pearson. “We do feel that there is much more potential for whales to sequester carbon through those indirect pathways, but because it's so intricate, we just aren't there yet with feeling comfortable putting a number on them.”

The concern is that, if whales’ role in carbon sequestration is overstated, companies could purchase carbon credits based on the animal’s preservation that wouldn’t actually offset their emissions.

“At the end of the day, we could end up with more harm to the climate than good,” Pearson says.

A humpback whale entangled in a fishing net is rescued by a Sea Shepherd crew inside a vaquita refuge in San Felipe, Baja California Norte, Mexico, in February 2020. There is a concern that, if whales’ role in carbon sequestration is overstated, companies could purchase carbon credits based on the animal’s preservation that wouldn’t actually offset their emissions. | SEA SHEPHERD / via REUTERS
A humpback whale entangled in a fishing net is rescued by a Sea Shepherd crew inside a vaquita refuge in San Felipe, Baja California Norte, Mexico, in February 2020. There is a concern that, if whales’ role in carbon sequestration is overstated, companies could purchase carbon credits based on the animal’s preservation that wouldn’t actually offset their emissions. | SEA SHEPHERD / via REUTERS

Given the uncertainty, Pearson and others are conducting or planning various experiments and research to fill in the scientific gaps. These range from taking seawater with phytoplankton in it and spiking it with whale feces to see the resulting effect on growth, to deploying sediment traps to measure the sinking particulate matter that emanates from whale feeding groups. Ultimately, scientists hope to feed this and other data into an “Earth system model” to get a sense of how the whole oceanic carbon cycle might be influenced by whales.

“We are starting to break down those steps of the indirect carbon pathways, and I think we have a pretty good handle of what we need to do to get at least our first order approximation of those indirect pathways,” Pearson says. “We just need some resources to get there.”

With the urgent need to protect and restore ecosystems and to maximize action on reducing the amount of carbon dioxide in the atmosphere, a key question naturally arises: Why not just do everything possible to conserve and increase whale populations?

“Promoting whale conservation is a low-risk, low-regret strategy,” Pearson says. “We're in the dual crises of biodiversity or extinction — however you want to call it — and climate, and whale conservation can help certainly with the biodiversity crisis and quite possibly with the climate crisis as well.”