The concept of natural carbon sinks is satisfyingly simple: the vegetation and animals that inhabit our terrestrial and marine biomes draw carbon from the atmosphere for use in their tissues. Great whales (including blue, humpback and sperm whales, among others), are so prodigious that they sequester millions of tonnes of carbon each year – an ecosystem service that an analysis from the International Monetary Fund (IMF) suggests is worth millions of dollars per whale to humanity.
Two factors make whales impressive carbon sinks. First, when great whales die, their bodies shuttle carbon down to the seafloor, a process known as ‘whale fall’. Each sinking whale carcass sequesters an average of 33 tonnes of CO2. Marine scientists estimate that the combined populations of the nine great whale species sequester 29,000 tonnes of carbon per year as whale fall.
Second, whales’ nutrient-rich faeces nourish phytoplankton at the sea surface, which increases their numbers. These microscopic powerhouses contribute 50 per cent of all oxygen in our atmosphere by capturing and converting 37 billion tonnes of CO2 per year.
One study by researchers at Flinders University in South Australia demonstrated that blue whales in the Southern Ocean increase the productivity of marine ecosystems by a metric of 240,000 tonnes of organic carbon per year in this way. Meanwhile, the 12,000 sperm whales of the Southern Ocean draw 200,000 tonnes of carbon out of the atmosphere each year through their phytoplankton support.
Largely due to the killing of whales throughout the 20th century, the amount of carbon stored by great whale populations today is estimated to be 9.1 million tonnes less than pre-industrial levels. The IMF have calculated that if blue whales alone recover to pre-industrial whaling levels, their contribution to marine carbon stocks will increase to 11 million tonnes of carbon per year, equivalent to preserving a temperate forest the size of Los Angeles.
To this end, the IMF has calculated the average value of a single great whale. To do so, it determined the value of the carbon each animal sequesters over its lifetime, factoring the amount of carbon that whales lock in by supporting phytoplankton. It then combined this figure with the market price of CO2.
Conservative estimates value a single great whale at more than US$2 million, meaning the Earth’s stock of the leviathans is valued at around US$1 trillion. A return to pre-whaling populations – which could capture 1.7 billion tonnes of CO2 annually – would be worth US$13 per person a year to subsidise. If we agree to pay the cost, ‘international financial institutions, in partnership with other UN and multilateral organizations, are ideally suited to advise, monitor and coordinate the actions of countries in protecting whales,’ write the IMF authors.