Wed Oct 11th, 2006 at 04:56:27 AM EST
There's more to the CO2 problem than warmth and weather. It's making the World Ocean more acidic, and ocean ecosystems are on track to be disrupted in ways that no one predict. With enough acid, shells and coral will dissolve.
Washington Post: Growing Acidity of Oceans May Kill Corals
The escalating level of carbon dioxide in the atmosphere is making the world's oceans more acidic, government and independent scientists say. They warn that, by the end of the century, the trend could decimate coral reefs and creatures that underpin the sea's food web.
Although scientists and some politicians have just begun to focus on the question of ocean acidification, they describe it as one of the most pressing environmental threats facing Earth.
"It's just been an absolute time bomb that's gone off both in the scientific community and, ultimately, in our public policymaking," said Rep. Jay Inslee (D-Wash.)...
The pH level, measured in "units," is a calculation of the balance of a liquid's acidity and its alkalinity. The lower a liquid's pH number, the higher its acidity; the higher the number, the more alkaline it is. The pH level for the world's oceans was stable between 1000 and 1800, but has dropped one-tenth of a unit since the Industrial Revolution, according to Christopher Langdon, a University of Miami marine biology professor.
Scientists expect ocean pH levels to drop by another 0.3 units by 2100, which could seriously damage marine creatures that need calcium carbonate to build their shells and skeletons. Once absorbed in seawater, carbon dioxide forms carbonic acid and lowers ocean pH, making it harder for corals, plankton and tiny marine snails (called pteropods) to form their body parts.
Ken Caldeira, a chemical oceanographer at Stanford University who briefed lawmakers along with NCAR marine ecologist Joan Kleypas, said oceans are [¶] more acidic than they have has [sic] been for "many millions of years."
[¶ The reporter got this wrong: pH would reach this level in 2100, if atmospheric CO2 concentrations were to increase unchecked.]
For a more reliable source than the above WaPo article, see:
Ocean acidification due to increasing atmospheric carbon dioxide (PDF, 1 MB)
(Royal Society, June 2005)
From what I've read, the process of ocean acidification is easier to model than climate change. Subject to various modulating influences, the effects of ocean circulation, and so forth, the basic story is that CO2 dissolves in water, forms carbonic acid, and lowers pH. Other influences make the story more complex, but nothing like climate change: acidification isn't nearly as sensitive to unknown forces, counter-forces, feedback loops, and messy, swirling weather patterns.
The effects of ocean acidification, however, seem less predictable than those of climate change.
Climate change, after all, is business-as-usual for Earth. Some regions become warmer, but most become no warmer than neighboring regions had been before. On the whole, species shift their ranges toward the poles, while polar bears shift their ranges northward past the pole and into the afterlife. Some regions become wetter or drier, but there have always been wet and dry places. Maybe the Gulf Stream shifts and Europe freezes, but little matter -- global climate has seen far greater changes in the last 20,000 years. By some standards (e.g., human) the expected disruptions may be enormous and unpredictable, but by other standards (e.g., planetary deep time), they're minor.
Now consider ocean acidification: On a planetary time scale, CO2 concentrations have sometimes been far higher than the highest projections for the next century, but this didn't make the seas more acid. Changes were slow and calcium carbonate minerals have always dissolved fast enough to buffer the ocean's chemistry. This process stabilized pH and kept calcium carbonate levels at saturation. Organisms (plankton, giant clams, coral...) could build up shells of calcium carbonate and not have them dissolve away instead.
Today, however, the atmospheric CO2 is rising far faster, too fast for calcium carbonate dissolution to keep up. The oceans are therefore on their way to being more acidic than they've been for... well... Caldeira simply says "many millions of years."
Note the difference: This is the whole ocean shifting outside its prior range. The analogy in the climatic case would be if all the temperature zones now on Earth shifted toward the poles and disappeared, leaving the whole world hotter than equatorial regions are today. And unlike the problem of rising global mean temperature, this one doesn't seem to have a cheap, easy fix.