The Oceans and Global Warming

The Oceans

Scientists have long understood the key role that oceans play in regulating the Earth's climate. Oceans cover 70 percent of the globe and store a thousand times more heat than the atmosphere does. What's newer is the understanding of how this key component of our climate system responds to global warming.

"Even five years ago most scientists had no inkling of the extent to which global warming was affecting the oceans—but slowly over the years a consensus has been building," says Environmental Defense marine ecologist Rod Fujita. Today, the scientific community believes there's plenty to worry about: changes are afoot in global ocean dynamics that could have profound ecological impacts.

A brake on global warming—for now

One of the ocean's most important climate functions is absorbing heat and carbon dioxide (CO2), one of the gases that causes global warming. Acting as a heat sponge, the oceans have absorbed huge amounts of heat and CO2 in the last forty years.

Fujita explains that "the oceans are saving us from faster climate change—in essence, they are a big flywheel that delays rapid overheating of the earth, putting a brake on the climate system."

"That's the good news," he adds. "The bad news is that the oceans only slow the atmospheric warming down. Once the oceans come to equilibrium with a greenhouse-gas warmed earth, the excess heat will remain in the atmosphere and things will get much hotter."

In effect, the oceans are taking up the slack for the atmosphere and delaying the full impacts of global warming. But where and how the oceans release this accumulated heat is uncertain. And as the ocean stores heat, fragile underwater ecosystems are struggling.

The most recent scientific report from the Intergovernmental Panel on Climate Change (IPCC) also notes with concern that the ocean is acidifying because of increased absorption of atmospheric CO2, and thus posing a threat for shell-forming species, which are an essential part of the marine food web. Projected increases in carbon dioxide levels will cause further acidification of the ocean. (IPCC, 2007)