It is well known that CO2 in the atmosphere has risen from about 275 ppm (.0275%) to 375 ppm (.0375%) since the Industrial Revolution began in the 1800s. This extra CO2, added to the atmosphere by the burning of fossil fuels, has contributed to the observed rise in global temperatures of 0.6 degrees C via the greenhouse effect. What is less well known, and is discussed in detail in a March 2006 article in Scientific American called "The Dangers of Ocean Acidification", is that a tremendous amount of the CO2 emitted by fossil fuel burning winds up in the oceans.
The oceans have absorbed 48% of all the CO2 emitted since 1800, according to a study published by Sabine et al. in 2004 in Science. Without the action of the oceans to absorb so much of our waste gases we've pumped into the atmosphere, Earth would be a seriously toasty planet right now.
The oceans are paying a price for this service, though. When CO2 dissolves into the ocean, it creates carbonic acid--the same acid found in soda pop. The oceans have dissolved so much CO2 during the past 150 years that the acidity of the oceans' surface waters has substantially increased. The pH, which decreases as acidity increases, used to range from 8.0 to 8.3 for the oceans' surface waters before the Industrial Revolution. This has now dropped a full 0.1 units to the 7.9 to 8.2 range. Unless significant cuts in CO2 emissions are realized in the next few decades, the pH will fall another 0.3 units by the year 2100 as the oceans continue to acidify. A 2005 report by the Royal Society of the UK projects the decrease by 2100 will be 0.5 pH units, and notes that it will take more than 10,000 years for the ocean to return to its pre-1800s acidity level.
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Ocean life can adapt to higher acidity. One study (Spivack et al., 1993) found that pH levels in the ocean 7.5 million years ago were about 7.4, well below today's pH. The big concern with the current increase in acidity and drop of ocean pH levels is that it is being compressed into such a short period of time. Past changes in oceanic acidity have presumably occurred over tens of thousands of years, giving time for life to adapt. The current change may occur so fast that a partial collapse of the food chain in some regions may occur. One note of optimism: similar concerns were voiced when the Antarctic ozone hole opened up, exposing phytoplankton in the Southern Hemisphere oceans to a rapid and unprecedented increase in levels of damaging ultraviolet radiation. It was widely feared that this increase in UV light would destroy enough phytoplankton to trigger a collapse of the food chain in the waters off of Antarctica. This has not happened. One study (Smith et. al., 1992) found a 6-12% decrease in phytoplankton during the time the ozone hole opens up, typically about 10-12 weeks of the year. So, at least in this one case, the marine ecosystem was able to adapt to a rapid, unprecedented change and not collapse.
As is the case with many aspects of human-caused climate change, the dangers are enormous, but poorly understood. In the words of the Dr. Doney's Scientific American article, "dramatic alterations in the marine environment appear to be inevitable." The Royal Society's article cautions, "research into the impacts of high concentrations of CO2 in the oceans is in its infancy and needs to be developed rapidly." The report goes on to state, "Ocean acidification is a powerful reason, in addition to that of climate change, for reducing global CO2 emissions. Action needs to be taken now to avoid the risk of irreversible damage to the oceans. We recommend that all possible approaches be considered of prevent CO2 reaching the atmosphere. No option that can make a significant contribution should be dismissed."
http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=312&tstamp=200603
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