When climate change leaped into global consciousness more than 20 years ago, the focus—as one might expect—was on the atmosphere. There was no doubt that sea levels would rise, with the expansion of warming oceans accompanied by a growing cascade of melt water from ice sheets and glaciers. But the main worry among policymakers and the public was how those rising seas would affect civilization, not on how the oceans themselves might be transformed.
Today, a growing body of evidence points to a web of changes already under way in ocean temperature, circulation, and biogeochemistry. These changes pose an array of risks to marine life that’s prompted a surge of research.
The best-known of the climate-related threats to ocean chemistry is acidification. The world’s oceans have soaked up roughly half a trillion tons of carbon dioxide, or about a third of all greenhouse gases produced by human activity since the Industrial Revolution. Because all that dissolved CO2 is weakly acidic, it’s been changing the pH balance of the oceans. On the logarithmic pH scale, the oceans—though still slightly alkaline—have moved toward acidity by about 0.1 point (roughly 30%).
It’s expected that future acidification could threaten a wide range of coral, shellfish, and other calcifying creatures. In 2009 Congress passed the Federal Ocean Acidification Research and Monitoring Act, and NOAA is now developing a strategic plan that will guide federal efforts to monitor and conserve marine life as pH values drop.
For those concerned about the fate of the sea and its residents, there’s another risk only recently recognized by scientists: widespread oxygen loss. Models now suggest that the amount of oxygen dissolved in Earth’s oceans could drop by anywhere from 1% to 7% by the year 2100, with much greater losses in some areas.
“This problem didn’t have a name a year and a half ago. It’s arisen only recently as a community-recognized concern,” says Ralph Keeling (Scripps Institution of Oceanography). He and a group of colleagues settled on the label “ocean deoxygenation” as Keeling began work on an overview of the topic that was published in 2010 by the Annual Review of Marine Science.
A review paper by Nicolas Gruber (ETH Zurich) soon to appear in Philosophical Transactions of the Royal Society sums up scientists’ new view of oceans with a succinct but ominous description: the seas are warming up, turning sour, and losing breath. “These three stressors will tend to affect the ocean at the same time, and in part, even synergistically,” says Gruber. “Once these changes have occurred, it will take centuries for the ocean to recover.”
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Bob Henson, UCAR Magazine, 11 March 2011. Full article.
