Whales: Earth’s giants drive oceanic carbon captureSeptember 2022

Sperm whale, Indian Ocean, Mauritius. Photo by Wonderful Nature.

Many proposed solutions to climate change, such as capturing carbon directly from the air and burying it deep in the earth, are complicated, costly, and unproven. What if nature offered us a “no-tech” alternative that was effective, economical, and available to scale up right now?

Look no further than the mighty whale.

Whales, particularly baleen and sperm whales, are among the largest creatures on Earth. Their bodies act as massive stores of carbon, while their presence shapes the marine ecosystems in which they live. We may think of trees doing the lion’s share of the work absorbing CO2 from the atmosphere, but in the oceans, these iconic animals play a hugely important role in the carbon cycle.

The astonishing carbon capture potential of large whales can be attributed to both the way they live and the way they die. Having accumulated an average of 30 tonnes of bodily carbon, these marine leviathans sink to the bottom of the ocean when their lives end. As their carcasses slowly decompose, the “blue” carbon inside them is gradually incorporated into marine sediment, removing it from the atmosphere for millennia.

Whale infographic for Animating the Carbon Cycle based on original design by GRID-Arendal

30K TONNES OF CARBON are carried to the bottom of the ocean every year by 8 species of baleen whale

A scientific study carried out in 2010 estimated that eight species of baleen whale – including the blue, humpback and minke whale – together carry 30,000 tonnes of carbon to the bottom of the ocean every year.

The authors also estimated that if populations of these whales were restored to pre-whaling levels, this carbon sink would increase by 160,000 tonnes a year.

How do the whales help store carbon?

• Carbon Storage in Bodies: Whales store significant amounts of carbon in their large bodies.
• Nutrient Cycling: Through swimming, diving, and defecating, whales increase nutrient levels in the ocean, especially iron and nitrogen.
• Boosting Phytoplankton Growth: The increased nutrients on the ocean surface enhance the growth of phytoplankton and marine plants.
• Carbon Capture by Phytoplankton: Phytoplankton and marine plants remove carbon from the atmosphere during photosynthesis.

Studies have found that the 12,000 sperm whales of the Southern Ocean support the capture of an estimated 200,000 tonnes of carbon every year through this mechanism.

Current situation – what we need to do

Today’s whale population of around 1.3 million animals is still recovering from commercial whaling, which was banned in 1986 (although some countries still flout the ban).

The total pre-whaling population of whales has been estimated at 4 to 5 million, although genetic analysis of whale populations in the North Atlantic suggests it may have been four to five times greater than this.

Regardless of the exact number, a continued whale comeback could significantly boost the amount of phytoplankton in the ocean and the atmospheric carbon it captures every year.

Researchers from the International Monetary Fund have estimated that a fully restored whale population may support the sequestration of more than 1.5 billion tonnes of CO2 every year. This is the equivalent of Russia’s annual anthropogenic CO2 emissions, or more than the annual anthropogenic CO2 emissions of the entire African continent.

To reach this point, we simply need to let the Earth’s whale populations – which still face multiple threats – recover.

Restoring baleen whale populations, (blue whale, fin whale, humpback whale, southern right whale and Antarctic minke whale) in the Southern Ocean could be equivalent to sequestering as much carbon per year as a forest almost twice the size of London.

Schmitz et al, 2023