Wednesday, March 3, 2010

Whales, Like Trees, Slow Warming

Whales are the largest animals on the planet, and when it comes to storing carbon, they act like trees in a forest.

blue whale

Whales, like the blue whale here, act like the world's forests, sucking climate-changing carbon dioxide out of the atmosphere over their lifetime and socking it away.


  • Whaling may have removed as much carbon from the oceans as deforesting much of northern New England.
  • Industrial whaling removed 90 -95 percent of many whale populations over the last 100 years.
  • Restoring whale populations may have the added benefit of sequestering carbon.

It's their parting gift to the world: Each dying whale carries tons of carbon to the sea floor as its massive body sinks, storing it there for centuries where it can't harm the climate.

In this way, whales are like the world's forests, sucking climate-changing carbon dioxide out of the atmosphere over their lifetime and socking it away. And according to new research, repopulating the oceans with whales could be as good for battling climate change as planting trees.

"If you think about whales and fish in terms of their carbon, there is a potential for using carbon offset credits as an additional incentive for rebuilding this population," said Andrew Pershing of the University of Maine School of Marine Science and the Gulf of Maine Research Institute who presented his results yesterday at a meeting of ocean scientists convened by the American Geophysical Union in Portland, Ore.

Conversely, Pershing noted, commercial whaling may have released large amounts of carbon dioxide into the atmosphere by pulling whales out of the ocean that would otherwise have fallen to the sea floor.

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Pershing estimates that whaling released around 105 million tons of carbon over the last 100 years -- as much carbon as burning most of Oregon's forests, or driving 128,000 Hummers for 100 years -- although these calculations carry several uncertainties.

While the amount of carbon possibly released by whaling over the last 100 years is small compared with the amount that is released annually worldwide -- 7 billion tons -- the amount is comparable to some of the proposed strategies for combating warming, like many reforestation projects or seeding the ocean with iron to increase CO2 uptake by phytoplankton, Pershing said.

Trees convert CO2 directly into wood and leaves through photosynthesis. Whales capture CO2 indirectly. Marine phytoplankton build their tissues through photosynthesis and are eaten by zooplankton, which whales then eat and use to build their colossal bodies. A 90-ton blue whale, the largest animal on Earth, holds about 9.4 tons of carbon, which would be converted to 34 tons of CO2 if it were burned or decomposed completely.

"One key difference between whales and forests is what happens when you've reached your steady state, your maximum population size," Pershing said.

At some point, the forest reaches its maximum density where dying trees are balanced by new growth, and the forest can no longer store any additional carbon, he said. "Marine systems are unique in that the animals and plant life in the surface waters of the ocean, when they die, they can take that carbon with them down to the bottom. A fully populated whale stock will continue to export carbon through sinking of dead whales."

And Pershing notes that other large top predators like bluefin tuna and sharks can have the same effect.

"These guys are huge. They don't have predators. When they die they are very likely to sink and take their biomass to the bottom of the ocean."

Over the last 100 years, whaling removed more than 2 million whales from the Southern Hemisphere alone, said Phillip Clapham, director of the cetacean program at the National Oceanic and Atmospheric Association's National Marine Mammal Laboratory in Seattle. For many species, this represented 90-95 percent of their total numbers.

Whale blubber was used to make margarine, as lamp or industrial oil, and the meat was sometimes consumed by animals or humans.

Some species have done better than others since the moratorium on whaling, which took effect in 1986. Humpback whales are doing extremely well in most places, Clapham said. But there are only about 2000 blue whales in the Antarctic now, compared to the 369,000 killed by whaling.

As for sequestering carbon, "It's a great idea. I love it." Clapham said. He cautions that he has no way of evaluating Pershing's calculations, but "presuming that they are correct, it certainly is a very novel and innovative idea and another reason to save whales."


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