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As it turns out, whales absorb a lot of climate-heating carbon in their bodies over the course of their long lives. And that makes them worth about $2 million each, by the International Monetary Fund’s estimates.

Researchers at the IMF put the giant mammals’ value so high — more than they’re worth dead on any market, in fact — because of their ability to take carbon out of the atmosphere. Even when whales die, that carbon stays stored in their corpses on the sea floor for centuries. Restoring the population of whales to pre-industrial levels, the researchers predicted in the December issue of the IMF’s magazine, would be the equivalent of planting four Amazon rainforests.

“We have to agree whales are an international public good,” Ralph Chami, the lead author of the IMF’s study, told National Geographic.

Whales not only store carbon in their own bodies but also help other animals do the same. Waters full of their poop nurture tiny organisms called phytoplankton, which produce half the oxygen in the atmosphere while mopping up huge amounts of carbon. The whales also eat krill, which eat phytoplankton. That’s a cycle, the IMF argues, that we should spend money to preserve.

And putting that $2 million price tag on whales helps policymakers calculate their return on investment for whale-protecting regulations.

Before industrial whaling took its toll on the whale population, an estimated 4 million to 5 million whales roamed the seas. The reason they were hunted is precisely the reason they’re so valuable now: Carbon-dense whale oil was a useful fuel. Now, scientists think there are just 1.3 million whales left.

Drastic measures are in the works to keep the planet from falling off the climate-change cliff, so to speak. Researchers are investigating whether spraying tiny particles into the upper atmosphere to reflect sunlight back into space is a reasonable way to keep the Earth from overheating. Others want to stimulate phytoplankton growth by dumping tons of iron directly into the ocean.

But all of these measures come with big risks, and no one knows exactly what ripple effects they might produce. Whales, on the other hand, are unlikely to destroy the planet in an effort to fix it.

“Nature has had millions of years to perfect her whale-based carbon sink technology,” the researchers wrote. “All we need to do is let the whales live.”