Point of view

In the oceans, the heat is really on

July 9, 2010 

It's not climate change, it's ocean change!

The oceans are choking on greenhouse gases. Our emissions are changing ocean temperature, pH and circulation with wide-ranging effects on biological productivity and ecosystem health. These are among the conclusions of five review articles published in a special feature on the oceans in a recent issue of Science magazine.

The world is saturated by coverage of the oil spill in the Gulf of Mexico. Yet the impacts of this tragedy are localized, short-term and trivial compared to the broader effects of climate change.

The oil spill has damaged the lives and businesses of many innocent people. Remarkably, however, every day we are releasing several thousand times as much carbon as the Gulf spill by driving, flying and consuming and by heating and cooling our energy-inefficient houses. Hundreds of years from now, when BP is forgotten and the gulf wetlands have healed, ocean life will still be affected by the fossil fuels we are burning today.

Nearly all of the debate - or at least what is depicted in the media as a debate - about global warming has focused on land surface temperatures. However, over 85 percent of the extra energy trapped by soaring greenhouse gases has gone into the ocean.

We all call this man-made catastrophe "global warming" or "climate change," but "ocean warming" and "ocean change" are really more descriptive of what is happening.

One value of the Gulf spill is that it has highlighted how tightly coupled the health of ecosystems and human economic well-being really are. In retrospect, the costs of preventing the spill by installing more reliable safety systems are paltry in comparison to the economic losses in the tourism and fisheries sectors. The same is true for mitigating climate change. Responses that cost less than 1 percent of GDP growth over the next few decades are matched against massive impacts on people and industry, especially in coastal areas of the world.

Greenhouse gas emissions are rapidly changing the physical properties and key biological process in the ocean. For example, declining primary productivity is affecting ocean food webs, fisheries and the ability of the ocean to naturally absorb and store greenhouse gases.

Other ominous signs loom. Deepwater dead zones have expanded, probably due to both local nutrient pollution as well as climate change. The melting of Arctic sea ice will allow thousands of species from the north Pacific to colonize the Atlantic. This will be the first mixing of the distinct biota of these regions in nearly a million years. Similar changes are expected in Antarctica, where warming is enabling marine predators to invade shallow-water ecosystems for which the freezing temperatures have been an effective barrier for 40 million years.

To avoid these uncertain worlds, a growing number of scientists from a range of fields have advocated that we keep the concentrations of atmospheric carbon dioxide below 450 ppm (parts per million). To achieve this, we need to cut global emissions by 5 percent per annum starting right now.

A tall order. However, we have no other alternative given the extremely high costs of inaction.

The good news is that there are plenty of solutions at hand, including investment in renewable energy systems or avoiding deforestation. National support for creating competitive renewable energy supplies would cause the required changes to ripple through global economies. Halting deforestation in Brazil and Indonesia would eliminate nearly 20 percent of greenhouse gas emissions. Protecting and restoring coastal vegetation, including mangroves, salt marsh and sea grasses - dubbed "blue carbon" - would maintain or increase the ability of marine ecosystems to capture and permanently store carbon dioxide. Furthermore, all of these solutions have huge benefits for people and biodiversity.

The world's scientists are calling for society and policymakers to wake up to the perils of our current greenhouse gas emission pathway. This is not merely the consensus of scientists; it is a consensus of evidence. Inaction might be justified if the impacts were trivial or there was nothing we could do to avoid these catastrophic futures. However, with so many affordable solutions in front of the world's nations, continued inaction is no longer an excuse.

John F. Bruno is an associate professor in the Department of Marine Science at UNC-Chapel Hill. Ove Hoegh-Guldberg is a professor and director of the Global Change Institute at the University of Queensland in Australia.

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