A study out in Nature today puts some long-term figures on a trend that climate scientists and ecologists have seen coming for some time: Oceans are no longer absorbing carbon dioxide from the atmosphere like they used to. Growing ocean acidity is slowing their ability to keep up as humans pump more and more greenhouse gases into the atmosphere.
The study, conducted by Samar Khatiwala of the Georgia Institute of Technology and colleagues, built a mathematical model of seawater changes over the past 20 years, including empirical data on temperature, salinity and the presence of manufactured chlorofluorocarbons, or CFC’s. Using information from the model, they estimated the rate of change of human-generated carbon in the sea from the year 1765, at the advent of the industrial era, until 2008.
Although oceans used to be able to keep up with the yearly rise in human-emitted carbon, absorbing more and more each year, Khatiwala’s study found that in the last 20 years, the oceans’ rate of absorption growth is slowing down. From 200 to 2007, the rate of increase dropped by about 10 percent. As Khatiwala told The New York Times:
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.
Khatiwala, S., Primeau, F., & Hall, T. (2009). Reconstruction of the history of anthropogenic CO2 concentrations in the ocean Nature, 462 (7271), 346-349 DOI: 10.1038/nature08526