Smarter Living: Travel & Recreation
How Carbon Dioxide is Altering the Oceans
Photo: Tim Donelly
Rising carbon dioxide emissions don't pose a problem in the atmosphere alone. The rising CO2 in our oceans is increasing acid levels, making seawaters more corrosive and threatening the survival of coral reefs and shelled sea creatures--the building blocks of ocean food chains and important sources of diet and income for coastal communities around the world. With pollution and overfishing already taking their toll on sea life, now is a dangerous time to subject ocean habitat to the added pressure of acidification and rising oceanic temperatures. These four factors are mutually reinforcing and could result in extinctions of marine life.
Although absorption of carbon dioxide by the oceans was once considered a buffer against the rapid rise of CO2 in the atmosphere, new evidence suggests that the ocean is absorbing CO2 at a rate of about 1 million metric tons per hour, according to Peter Brewer of Monterey Bay Aquarium Research Institute. As a result, global seawater is acidifying faster than it has for 55 million years. Pacific seawater between Oahu, Hawaii and Kodiak, Alaska has jumped six percent in acidity from 1991 to 2006, according to a fifteen-year study published in the American Geophysical Union's journal Geophysical Research Letters and conducted by scientists from 11 academic institutions and two National Oceanic and Atmospheric Administration research labs. Scientists now worry that many ocean organisms won't adapt quickly enough to survive.
The last ocean acidification event that can compare in magnitude occurred when the planet shifted from an ice age to a warmer climate 55 million years ago and large numbers of deep-water ocean organisms went extinct, according to researchers Dr. Daniella Schmidt and Dr. Andrew Ridgwell at the University of Bristol.
Already, the oceans are 30 percent more acidic than pre-industrial levels and, unless carbon emissions are curbed, they could be twice as acidic at the end of the century as they are today. We may lose species that we never knew we had. Just last fall 5,600 previously unknown species were listed in the Census of Marine Life.
The Ills of Acidic Oceans
What do we know is already happening? As the percentage of carbonic acid in the ocean increases, it leads to less calcium carbonate, an essential building block for the shells that house "calcifying" organisms. Samples from Antarctica of the shells of tiny marine organisms--foraminifera or "forams"--dating to roughly 50,000 years ago compared with foram shells from the period 1997 to 2004 show an average of a 30 percent lower weights in the recent shells compared with those in the ancient baseline group, according to a study published online in Nature Geoscience on March 8, 2009. The study authors note that if this loss in shell weight is typical of a wider a selection of forams it could have a significant effect on the carbon cycle. By implication, this could mean less oceanic absorption of CO2 and thus still higher atmospheric levels.
Not only is shell growth affected, if waters become acidic enough, existing shells will begin to dissolve. Water acidic enough to corrode some types of shells has welled up along the West coast and, without a reduction in carbon emissions, models predict that vast portions of the Southern and the Arctic Ocean will be corrosive to some shelled organisms by mid century.
Coral reefs, already suffering from threats including nutrient runoff and overfishing, are especially sensitive to acidification. Certain corals struggle to make new skeletons in seawater with high levels of CO2 and existing coral skeletons can dissolve. With one in four ocean species living in a coral reef, reefs are invaluable habitats that often stock many of the food basics for coastal communities, while generating tourism revenue and protecting coastlines from storms. Sarah Cooley, marine chemist and post-doctoral researcher at WHOI, has estimated the monetary cost of losing the remaining earth's coral reef protection and fisheries to be in upwards of $30 billion a year.
Vestiges of Hope and How to Help
Fortunately, scattered throughout the evidence pointing to acidification's ills are some reasons for hope. According to NRDC senior scientist Lisa Suatoni, "there isn't a huge delay with ocean acidification, like there is with global warming. If we stopped producing CO2, we would stop acidifying the ocean. But we have to take action urgently," she insists.
In addition, we can help these ecosystems along by improving ocean health. According to Suatoni, the ocean is a resilient place, and given the opportunity and enough time, it can heal itself. Laboratory experiments that show how detrimental acidified water is to organisms don't account for the possibility that organisms will adapt via migration or evolution. We can help improve the health of marine ecosystems, says Suatoni, by establishing marine protected areas, working to restore depleted fish populations and by reducing nutrient pollution in the coastal zones. With stronger and healthier ecosystems, ocean organisms will have a fighting chance of adapting to their changing environment.
Here are some steps each of us can take to help:
- Keep striving to reduce your own carbon footprint, by driving less, consuming less energy in the home and investing in green energy. Measure your footprint with our carbon calculators, keep track of improvements and compare your results with others by joining our CO2 Smackdown.
- Consume only sustainably caught seafood to help limit the stress put on dwindling fish populations.
- Avoid products, such as fertilizers, that contain added nitrogen, which can seep into waterways and contribute to nutrient pollution.
- When you go to the ocean, use sunscreens with plant-based ingredients, as some chemical preservatives and stabilizers in sunscreens can damage coral reefs.
- Wash your car at a car wash to keep oil, brake fluid and other chemicals from running off your driveway and into the stormwater system which will eventually result in their ending up untreated and in the ocean.
See NRDC's acidification resources, including the film Acid Test: The Global Challenge of Ocean Acidification and the Oceans program report Ocean Acidification: The Other CO2 Problem.
For the ocean absorbing CO2 at a rate of about 1 million metric tons per hour:
Brewer, P.G. 2010. "A changing ocean seen with clarity." PNAS vol 106, no. 30.
For global seawater acidifying at a rate unsurpassed for 55 million years:
Ridgwell, A. and D. Schmidt. 2010. Past constraints on the vulnerability of marine calcifiers to massive carbon dioxide release. Nature Geoscience 3, 196 – 200
For the acidity of Pacific seawater between Oahu, Hawaii and Kodiak, Alaska rising six percent from 1991 to 2006:
Byrne, R. H., S. Mecking, R. A. Feely, and X. Liu (2010), Direct observations of basin-wide acidification of the North Pacific Ocean. Geophys. Res. Lett., 37, L02601, doi:10.1029/2009GL040999.
For oceans currently being 30% more acidic than pre-industrial levels:
Caldeira, K. and M. E. Wickett. 2003. Anthropogenic carbon and ocean pH. Nature 425:365-365
For the potential for oceans to become three times as acidic at the end of the century as they are today and models predicting that vast portions of the Southern and the Arctic Ocean will be corrosive to shells by mid century:
Orr, J. C., V. J. Fabry, O. Aumont, L. Bopp, S. C. Doney, R. A. Feely, A. Gnanadesikan, N. Gruber, A. Ishida, F. Joos, R. M. Key, K. Lindsay, E. Maier-Reimer, R. Matear, P. Monfray, A. Mouchet, R. G. Najjar, G. K. Plattner, K. B. Rodgers, C. L. Sabine, J. L. Sarmiento, R. Schlitzer, R. D. Slater, I. J. Totterdell, M. F. Weirig, Y. Yamanaka, and A. Yool. 2005. Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature 437:681-686.
For decreasing carbonic acid levels in the ocean leading to less calcium carbonate for shells:
Doney, S. C., V. J. Fabry, R. A. Feely, and J. Kleypas. 2009. Ocean Acidification: The Other CO2 Problem. Annual Review of Marine Sciences 1:169-192.
For lower weights of "foram" shells:
Moy et al. "Reduced calcification in modern Southern Ocean planktonic foraminifera." Nature Geoscience, e-pub March 8, 2009.
For upwelling of corrosive water on the West coast:
Feely, R. A., C. L. Sabine, J. M. Hernandez-Ayon, D. Ianson, and B. Hales. 2008. Evidence for upwelling of corrosive "acidified" water onto the continental shelf. Science 320:1490-1492.
For corals struggle to make new skeletons in seawater with high levels of CO2 and existing coral skeletons dissolving:
Kleypas, J. A., & Yates, K. K., 2009. Coral reefs and ocean acidification. Oceanography 22(4): 108-117.
For one in four ocean species living in a coral reef:
Spalding M, Ravilious C, Green EP (2001) World Atlas of Coral Reefs. Univ. of California Press
For the estimated $30 billion a year cost of losing the remaining earth’s coral reef protection and fisheries:
Cooley, Sarah R.; Kite-Powell, Hauke L.; Doney, Scott C. (2009) Ocean acidification’s potential to alter global marine ecosystem services. Oceanography, Volume 22, Number 4.
last revised 1/30/2012