September 20, 2007
Ocean Acidification Seen From Rising Carbon Dioxide

A rise in atmospheric carbon dioxide to 500 parts per million (ppm) will cause a lowering of ocean acidity by 0.2 pH and that is probably a bad development.

“About 1/3 of the CO2 from fossil-fuel burning is absorbed by the world’s oceans,” explained lead author Ken Caldeira from the Carnegie Institution Department of Global Ecology. “When CO2 gas dissolves in the ocean it makes carbonic acid which can damage coral reefs and also hurt other calcifying organisms, such as phytoplankton and zooplankton, some of the most critical players at the bottom of the world’s food chain. In sufficient concentration, the acidity can corrode shellfish shells, disrupt coral formation, and interfere with oxygen supply. ”

Most of the research today points to a future where, in the absence of a major effort to curtail carbon dioxide emissions, there will be double the atmospheric concentrations of CO2 (760 parts per million, or ppm) by century’s end. Atmospheric carbon dioxide concentrations could reach 500 ppm by mid-century. Pre-industrial concentrations, by comparison, were 280 ppm and today's concentration is about 380 ppm.

The acidity from CO2 dissolved in ocean water is measured by the pH scale (potential of Hydrogen). Declines in pH indicate that a solution is more acidic. The U.S. Environmental Protection Agency [1976] Quality Criteria for Water state: “For open ocean waters where the depth is substantially greater than the euphotic zone, the pH should not be changed more than 0.2 units outside the range of naturally occurring variation …” The euphotic zone goes to a depth of about 650 feet (200 meters), where light can still reach and photosynthesis can occur.

“Atmospheric CO2 concentrations need to remain at less than 500 ppm for the ocean pH decrease to stay within the 0.2 limit set forth by the U.S. Environmental Protection Agency [1976],” remarked Caldeira. “If atmospheric CO2 goes above 500 ppm, the surface of the entire ocean will be out of compliance with EPA pH guidelines for the open ocean. We need to start thinking about carbon dioxide as an ocean pollutant. That is, when we release carbon dioxide to the atmosphere, we are dumping industrial waste in the ocean.”

I have previously argued that since we can easily cool the Earth (even cause an Ice Age for less than $1 billion per year) using either silicon dioxide or dimethyl sulfide (DMS) that the main problem with atmospheric CO2 build-up the dissolving of atmospheric CO2 into the oceans making them too acidic. I've yet to come across any proposed methods for preventing ocean acidification. Also, it is not clear how much harm to marine life will come from a shift of pH down by 0.2.

Atmospheric CO2 might never reach 500 ppm. The rising cost of oil extraction will combine with future declines in the costs of nuclear and solar power to cause a shift away from fossil fuels and toward energy sources which are not net producers of carbon dioxide emissions.

Share |      Randall Parker, 2007 September 20 08:42 PM  Climate Trends

rsilvetz said at September 20, 2007 9:39 PM:

The impact of 0.2 ph points is negligible. Plus the model is unlikely to hold up in reality given both the oceans size and overall stability of the ecosystem.

Paul Dietz said at September 21, 2007 10:42 AM:

Ocean acidification could be addressed by dissolving finely ground limestone (calcium carbonate) into the ocean, but the quantities involved would be staggered, many billions of tons. This would be an acceleration of the natural buffering process that will increase ocean pH over the roughly thousand year timescale.

Frederick J Barclay said at October 1, 2008 11:44 AM:

My book gives a way to combat worsening ocean acidification! Title "Fuel Cells Engines and Hydrogen, an Exergy Approach." By Frederick J Barcolay. The message is that the heat engine must be phased out world wide in a UN sized and politically unpopular project of onerous expense, and replaced by Fuel Cells using "isothermal oxidation" to give an up to 400% increase in fossil fuel efficiency of use. The adverse equilibrium which imperils the food chain via coral and plankton damage, will be rebalanced the air purified and the sea sweetened.

Discussion most welcome.

F J Barclay Studio23B Limehouse Cut 46 Morris Rd Poplar London E14 6NQ


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