By Kathy Tedesco, Program Manager, NOAA/OGP
Richard A. Feely, NOAA/PMEL
Christopher L. Sabine, NOAA/PMEL
Cathrine E. Cosca, NOAA/PMEL

Last April, a NOAA/NSF/USGS-sponsored workshop at the USGS Center for Coastal Studies in St. Petersburg, Florida revealed potential future problems for marine ecosystems from ocean acidification (see workshop highlights). A group of fifty international experts discussed how the release of the huge amounts of carbon dioxide from fossil-fuel burning, land-use practices, and cement production will affect the chemistry and biology of the oceans. For 400,000 years prior to the industrial revolution, atmospheric CO2 concentrations remained between 200 to 280 parts per million (ppm). As a result of the industrial and agricultural activities of humans, current atmospheric CO2 concentrations are around 380 ppm, increasing at about 1% per year. Over the past two decades, only half of the CO2 released by human activity, the so-called “anthropogenic CO2,” has remained in the atmosphere; about 30% has been taken up by the ocean, and 20% by the terrestrial biosphere. The atmospheric concentration of carbon dioxide is now higher than experienced on Earth for at least the last 400,000 years, and is expected to continue to rise, leading to significant temperature increases by the end of this century.

The global oceans are the largest natural reservoir for this excess carbon dioxide, absorbing approximately one-third of the carbon dioxide added to the atmosphere by human activities each year, and over the next millennium, is expected to absorb approximately 90% of the CO2 emitted to the atmosphere. It is now well established that there is a strong possibility that dissolved CO2 in the ocean surface will double over its pre-industrial value by the middle of this century, with accompanying surface ocean acidity (pH) and carbonate ion (CO32-) decreases that are greater than those experienced during the transition from ice ages to warm ages. The uptake of anthropogenic CO2 by the ocean changes the chemistry of the oceans and can potentially have significant impacts on the biological systems in the upper oceans. Estimates of future atmospheric and oceanic CO2 concentrations, based on the Intergovernmental Panel on Climate Change (IPCC) emission scenarios and general circulation models that include the biogeochemical cycles of carbon and nutrients, indicate that by middle of this century atmospheric CO2 levels could be reach over 500 ppm, and near the end of the century they could be over 800 ppm. Corresponding models for the oceans indicate that surface water acidity (pH) drop would be approximately 0.4 pH units, and the carbonate ion concentration would decrease almost 50 % by the end of the century. This surface ocean pH drop would be lower than it has been for more than twenty million years. A pH reduction of approximately 0.1 unit in surface waters has occurred already due to oceanic uptake of anthropogenic CO2.

NOAAIf all the oceans were currently saturated with CO2, we would be in much bigger trouble than we are already.