Coral reefs may start dissolving when atmospheric CO2 doubles


Stanford, CA– Rising carbon dioxide in the atmosphere and the resulting effects on ocean water are making it increasingly difficult for coral reefs to grow, say scientists. A study to be published online March 13, 2009 in Geophysical Research Letters by researchers at the Carnegie Institution and the Hebrew University of Jerusalem warns that if carbon dioxide reaches double pre-industrial levels, coral reefs can be expected to not just stop growing, but also to begin dissolving all over the world.

The impact on reefs is a consequence of both ocean acidification caused by the absorption of carbon dioxide into seawater and rising water temperatures. Previous studies have shown that rising carbon dioxide will slow coral growth, but this is the first study to show that coral reefs can be expected to start dissolving just about everywhere in just a few decades, unless carbon dioxide emissions are cut deeply and soon.

“Globally, each second, we dump over 1000 tons of carbon dioxide into the atmosphere and, each second, about 300 tons of that carbon dioxide is going into the oceans,” said co-author Ken Caldeira of the Carnegie Institution’s Department of Global Ecology, testifying to the U.S. House of Representatives Subcommittee on Insular Affairs, Oceans and Wildlife of the Committee on Natural Resources on February 25, 2009. “We can say with a high degree of certainty that all of this CO2 will make the oceans more acidic – that is simple chemistry taught to freshman college students.”

The study was designed determine the impact of this acidification on coral reefs. The research team, consisting of Jacob Silverman, Caldeira, and Long Cao of the Carnegie Institution as well as Boaz Lazar and Jonathan Erez from The Hebrew University of Jerusalem, used field data from coral reefs to determine the effects of temperature and water chemistry on coral calcification rates. Armed with this information, they plugged the data into a computer model that calculated global seawater temperature and chemistry at different atmospheric levels of CO2 ranging from the pre-industrial value of 280 ppm (parts per million) to 750 ppm. The current atmospheric concentration is over 380 ppm, and is rapidly rising due to human-caused emissions, primarily through the burning of fossil fuels.

Based on the model results for more than 9,000 reef locations, the researchers determined that at the highest concentration studied, 750 ppm, acidification of seawater would reduce calcification rates of three quarters of the world’s reefs to less than 20% of pre-industrial rates. Field studies suggest that at such low rates, coral growth would not be able to keep up with dissolution and other natural as well as manmade destructive processes attacking reefs.

Prospects for reefs are even gloomier when the effects of coral bleaching are included in the model. Coral bleaching refers to the loss of symbiotic algae that are essential for healthy growth of coral colonies. Bleaching is already a widespread problem, and high temperatures are among the factors known to promote bleaching. According to their model the researchers calculated that under present conditions 30% of reefs have already undergone bleaching and that at CO2 levels of 560 ppm (twice pre-industrial levels) the combined effects of acidification and bleaching will reduce the calcification rates of all the world’s reefs by 80% or more. This lowered calcification rate will render all reefs vulnerable to dissolution, without even considering other threats to reefs, such as pollution.

“Our fossil-fueled lifestyle is killing off coral reefs,” says Caldeira. “If we don’t change our ways soon, in the next few decades we will destroy what took millions of years to create.”

“Coral reefs may be the canary in the coal mine,” he adds. “Other major pieces of our planet may be similarly threatened because we are using the atmosphere and oceans as dumps for our CO2 pollution. We can save the reefs if we decide to treat our planet with the care it deserves. We need to power our economy with technologies that do not dump carbon dioxide into the atmosphere or oceans.”


2 Responses to Coral reefs may start dissolving when atmospheric CO2 doubles

  1. Mike42 March 14, 2010 at 12:24 pm #

    David,

    As the article states the researchers “used field data from coral reefs to determine the effects of temperature and water chemistry on coral calcification rates”. Here is a link to the research paper: {I can’t include links. Use Google.]

    Citation: J. Silverman, B. Lazar, L. Cao, K. Caldeira, and J. Erez (2009), Coral reefs may start dissolving when atmospheric CO doubles, Geophys. Res. Lett., 36, L05606, doi:10.1029/2008GL036282.

    I don’t not know about the changes in coral reefs in past ages, but I did fibd an article that explains that if the rate of change in atmospheric CO2 is slow, then ocean pH does not change much because of buffering effects.

    “When a CO2 change occurs over a short time interval (that is, less than about 10^4 yr), ocean pH is relatively sensitive to added CO2. However,
    when a CO2 change occurs over a long time interval (longer than about 10^5 yr), ocean chemistry is buffered by interactions with carbonate minerals, thereby reducing sensitivity to pH changes.”

    See: [I can’t include the URL. Use Google} Nature 425, 365 (25 September 2003) | doi:10.1038/425365a. Oceanography: Anthropogenic carbon and ocean pH by Ken Caldeira1 & Michael E. Wickett2

    Note: you may need a subscribtioon to view these articles. If so, go to a near by university library a look them up there.

  2. Anonymous March 10, 2009 at 8:31 am #

    In Gore’s presentation, the carbon dioxide levels were several times those of the present era for millions of years at a time. Why did not the coral reefs dissolve during those periods?

    Are there coral species whose coral does not readily dissolve ? Are there coral species that react to increased CO2 levels by increasing their production of calcium ?

    Did the research team conduct any lab work to verify their computer models. E.G. Did they take real coral and drop it into vats of sea water with varying amounts of CO2 to determine how long they took to dissolve.

    I work with computer models in a different discipline. The greatest problem is engineers and researchers who do not bother to validate their models against real world data prior to releasing the results. There are too many confounding variables in the environment of coral reefs to make these statements without doing significant lab work with sizable chunks of living coral reef and its denizens. Recall that the coral reefs have successfully made it thru several extended periods of high atmospheric CO2 levels radically higher then any currently anticipated under the worst scenarios. How did the coral do this and what makes this period different. Unless the modelers can answer this question with real world lab data demonstrating that this period is chemically different or that modern coral responds differently today then ancient coral did during the previous high CO2 periods, the validity of their math models must remain suspect.

    Remember with computer models, the sequence is do the theory, make the model, validate the model against one set of real world data, throw the model out and redo it so that it validates against the real world data, run the model again, calibrate against a second set of real world data.

    The key is the extensive real world experiments to gather validation and calibration data which were not mentioned in the article.

    Thank you,
    David Gibson, MSCE, PE

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