A century of whaling may have released more than 100 million tonnes - or a large forest's worth - of carbon into the atmosphere, scientists say.
Whales store carbon within their huge bodies and when they are killed, much of this carbon can be released.
US scientists revealed their estimate of carbon released by whaling at a major ocean sciences meeting in the US.
Dr Andrew Pershing from the University of Maine described whales as the "forests of the ocean".
Dr Pershing and his colleagues from the Gulf of Maine Research Institute calculated the annual carbon-storing capacity of whales as they grew.
"Whales, like any animal or plant on the planet, are made out of a lot of carbon," he said.
"And when you kill and remove a whale from the ocean, that's removing carbon from this storage system and possibly sending it into the atmosphere."
He pointed out that, particularly in the early days of whaling, the animals were a source of lamp oil, which was burned, releasing the carbon directly into the air.
"And this marine system is unique because when whales die [naturally], their bodies sink, so they take that carbon down to the bottom of the ocean.
"If they die where it's deep enough, it will be [stored] out of the atmosphere perhaps for hundreds of years."
In their initial calculations, the team worked out that 100 years of whaling had released an amount of carbon equivalent to burning 130,000 sq km of temperate forests, or to driving 128,000 Humvees continuously for 100 years.
THESE CO2OPHOBES NEED TO GET THEIR HEADS EXAMINED.