No, whales aren’t huge carbon capture machines

While they’re crucial to ocean ecosystems, whales should not be counted on to provide any meaningful greenhouse gas reductions, according to new research.

The idea of carbon-sequestering whales has drawn public interest on the basis that whale poo promotes blooms of CO₂-absorbing phytoplankton, which sink to the bottom of the ocean when they die. This means they’re storing carbon that’s been removed from the atmosphere.

But a team of Australian and South African researchers has found that whales don’t make a significant difference to the global carbon cycle.

They’ve published their findings in Frontiers in Marine Science.

“It’s a feel-good story, that whales are also good for capturing carbon. And there is some truth in it. But they’re not going to save us from climate change,” lead author Dr Olaf Meynecke, a marine scientist at Griffith University, tells Cosmos.

The ocean absorbs about a quarter of anthropogenic CO₂ emissions, and generates around half the world’s oxygen.

Much of that absorption and oxygen comes from photosynthesising phytoplankton, so anything that promotes phytoplankton growth (like whales) has an effect on the carbon cycle – but Meynecke stresses that this is “not a direct link”.

“We sourced all the available information to see: what does the science actually tell us? What do we currently know about the global carbon cycle, and how do the whales fit in?,” he says.

“When we look at the numbers, they just don’t really tell a story that whales are going to have a significant impact on the global carbon cycle. They will have an impact on smaller scales, maybe at a regional scale, but unfortunately, not at a global scale.”

It’s previously been suggested that carbon credits could be sold to fund whale conservation. Meynecke thinks this idea is ill-advised.

“As a researcher running a whales and climate program, I would like to have whales be the solution for our carbon problems, and it would be wonderful if we could promote this and maybe even fund our research from it,” he says.

“But I think it’s a very dangerous path to go down, to basically claim something that hasn’t got the validation. Then people put their hopes and money into it, but we’re not really changing the problem.

“We know mangroves, salt marshes, and sea grasses are really good at capturing carbon, because they put it into their roots and into the soil. That’s a scientifically proven method.

“So it’s important that we keep in mind there are solutions in the ocean. It’s really important to keep the ocean healthy, because that’s probably the best way of continuing the carbon capture that the ocean does.”

They may not be huge carbon sinks, but whales are still vital to ocean ecosystems for other reasons.

“Large scale protection of marine environments including the habitats of whales will build resilience and assist with natural carbon capture,” conclude the authors in their paper.

Update, 6 June 2023: A previous version of this article suggested that whales eat phytoplankton – this is incorrect and has been adjusted.