The Irrefutable Link: CO2 and Ocean Acidification

 “It is very complicated to pin the heating of the planet on a single gas, but ocean acidification involves straightforward chemistry” - Robert B. Dunbar, professor of geological and environmental sciences at Stanford University

Dear readers,

Hope you've all been having a great weekend! In the last post, we talked about how rising atmospheric carbon dioxide (CO2) levels have contributed to the increased acidification of the oceans. For a quick review, when CO2 comes into contact with salt water, it reacts to form several chemical species. One of these is carbonic acid (H2CO3), which, when it dissociates in water, produces free hydrogen (H+) ions. The concentration of hydrogen ions in a solution (H+) determines the solution's acidity.

The oceans have been acting as a giant sponge for CO2, absorbing more than 50% of human emitted CO2. As a result, rising CO2 levels, caused by the burning of fossil fuels, have directly caused the ocean's pH (acidity measure) to drop from 8.179 during the 1700s to 8.069 right now. While this decrease of 0.11 pH units may not seem large, since pH is calculated on a logarithmic scale, this actually translates to a 30% increase in acidity*!! Furthermore, projections for year 2100, which are based on current CO2 emissions levels, predict that ocean pH will drop by an additional 0.3-0.5 units, becoming approximately 150% more acidic! A drop in pH that large hasn't been seen in 20 million years and will have profound effects on marine flora and fauna.

So, while it may be difficult to pinpoint whether the exact cause of global warming is the increased CO2 emissions of the 20th and 21st century, the case of ocean acidification is directly and cleanly linked to increased anthropogenic CO2 emissions. Thus, in the oceans we can most clearly see our impact on the global environment.

-N. Gallo

The Dissolving Truth: A pteropod shell placed for 45 days in ocean water under 2100 projections. The next entry will more specifically address how ocean acidification affects calcification. (photo credit: http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F)

*(To avoid confusion, I should note that the oceans are not actually acidic. On the pH scale, anything that is below 7 pH units is considered acidic, so the oceans are still alkaline at a pH of 8.069. However, most marine organisms are extremely sensitive to pH changes, and the oceans are rapidly becoming more acidic/less basic).

Good links for further reading
1. "What Is Ocean Acidification?" -  http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F
2. "Ocean Acidification: A Global Case of Osteoporosis" - http://discovermagazine.com/2008/jul/16-ocean-acidification-a-global-case-of-osteoporosis/article_view?b_start:int=0&-C=
3. "Covering Ocean Acidification: Chemistry and Considerations" - http://www.yaleclimatemediaforum.org/2008/06/covering-ocean-acidification-chemistry-and-considerations/
4. "The Acid Ocean - The Other Problem with CO2 Emission" - http://www.realclimate.org/index.php/archives/2005/07/the-acid-ocean-the-other-problem-with-cosub2sub-emission/