Earth’s oceans face a perilous future

According to a study in Sunday’s edition of the journal Nature Geoscience, humanity’s carbon-emitting ways could significantly affect the future of the planet’s oceans. Gary Schaffer, author of the study and a professor at the University of Copenhagen, examined the ocean’s long-term reactions to anthropologic emissions and current patterns of climate change.

In the worst scenario, society continues to burn fossil fuels at its current rhythm. The atmosphere’s carbon dioxide concentration quadruples and the planet’s mean temperature increases by 9 degrees Fahrenheit.

Subsequently, the seas absorb an increasing amount of CO₂ from the skies. The oceans, in turn, become more acidic as the CO₂ fuses with H₂O. The chemical equation for the process is swift and direct:

CO₂ (g) + H₂O(l) → H₂CO₃ (aq)
Carbon dioxide + water → carbonic acid

The increase in acidity causes the oceans’ pH to drop. As a consequence, the oceans’ dissolved oxygen (O₂) levels follow a similar pattern. Warmer waters, the result of global warming and rising anthropologic CO₂ emissions, accelerate the acidification process. The naturally low dissolved oxygen levels associated with warm waters further exacerbate the effects of oxygen depletion. If the oxygen level falls too low, entire swaths of ocean can become what marine biologists call “dead zones” – places where oxygen levels are too low to support multi-cellular organisms.

Currently, about two percent of the oceans’ area qualifies as a dead zone. Should the worst-case scenario come to pass, the study says, that number could inflate to 20 percent of the oceans’ area within the next 100,000 years. However, the effects would become immediately noticeable by the end of the century and omnipresent within a few millennia.

If humans halt carbon emissions by the end of the century, air temperatures will climax by 2200. The seas, acidified and heated, will continue to warm up for another two or three thousand years before stabilizing. The rising temperatures could squelch as much as 50 percent of the sea’s dissolved oxygen, while the falling pH would threaten all shelled marine creatures. The carbonic acid, created as seawater absorbs atmospheric CO₂, reacts with the calcium carbonate (CaCO₃) found in the skeletons of corals and the exoskeletons of mollusks and zooplankton.

To make matters worse, warming waters could threaten global ocean currents by stopping their circulation. That, fed by a continuous stream of carbon emissions, would feed massive cyanobacteria blooms. As ecosystems collapse, the bacteria could release the toxic gas hydrogen sulfide into the atmosphere.

It is believed the marine portion of the Permian Mass Extinction, which wiped out 90 percent of life on Earth 250 million years ago, was caused by this process.

February 4, 2009


Andrew Blitman

Science Columnist

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