In an article published in the NY Times (http://www.nytimes.com/2009/11/19/science/earth/19oceans.html?_r=1&ref=science), Sindya N. Bhanoo describes the decreasing efficiency with which our planet's oceans absorb CO2. Apparently Earth's oceans are no longer able to absorb CO2 as well as they did in the pre-industrial era. Samar Khatiwala was the lead author of a 20 year study which collected tens of thousands of ocean samples. Their research enabled them to estimate the efficiency with which the oceans absorbed carbon dioxide each yeah from 1965 to 2008.
Earth's oceans have long been considered dependable "carbon sinks" by the scientific community at large. This study suggests that this logic, while sound for now, may not always be the case. As humans continue to burn fossil fuels at alarming rates, carbon emissions into the atmosphere consistently increase. The oceans are now overtaxed; the more CO2 they are forced to absorb, the more acidic they become. This is a serious problem because as the oceans grow more acidic, they are even less efficient at absorbing CO2. Put simply, the more carbon emissions an ocean absorbs, the worse it becomes at absorbing more CO2. So now, Earth's oceans are stuck in a positive feedback system with CO2, and the situation will continue to worsen.
According to Khatiwala, "It’s a small change in absolute terms. What I think is fairly clear and important in the long-term is the trend toward lower values which implies that more of the emissions will remain in the atmosphere." If we cannot rely on our oceans to help relieve some of the CO2-induced stress on the atmosphere, the greenhouse effect will become even more profound.
Khatiwala's findings are supported by a 2004 study done by Christopher Sabine. Sabine's team investigated carbon uptake levels in the oceans up to 1994, by collecting data on more than 100 cruise ships. Each team used slightly different methods, but their conclusions are in accordance with one another. Khatiwala reports that "the oceans’ uptake rate growth appears to have dropped by 10 percent from 2000 to 2007." Much of, if not all, this decrease in efficiency can be attributed to increasing human-generated CO2 emissions. This cycle is almost certain to continue unless there is a significant decrease in CO2 emissions, which would have to result from a decrease in fossil fuel consumption.
The end of the article does mention something interesting, and possibly optimistic. Khatiwala's team also estimated CO2 absorption by land, and their conclusion was that Earth's land was actually absorbing more CO2 than it was admitting. Khatiwala admits to not being "land people", but their hypothesis is that land plant's could be consuming more CO2 in order to grow bigger. However, they said that while their research about land absorption was interesting, it up to another team to conduct further research. If the oceans are becoming less adapt at absorbing carbon emissions, perhaps hope can be found if we find a way to take advantage of the absorption efficiency of Earth's land.