Coral Reefs are the tropical rain forests of the ocean, the most biologically diverse and spectacular biological features on earth. 20% of them are already dead because of warming, acidifying oceans, pollution and directly destructive human activities.
In the geological record, ocean acidification is the most destructive problem of all because it takes nature hundreds of thousands to millions of years to restore balance. The greatest of all extinctions in the oceans was the Permian extinction where 80% of species went extinct. This extinction happened when CO2 levels rose so quickly that the ocean became too acidic to support coral reefs and carbonate shelled organisms dissolved into oblivion. Coral polyps survived extinction by living as free floating unshelled organisms. We are beginning to recreate the conditions of the great Permian extinction.
Coral reefs are in trouble across the globe. At the local level pollution and abuse of reefs has caused disease and destruction. On the global scale there are two large interrelated problems, global warming and global acidification of the oceans. These problems have been caused by industrial-scale burning of fossil fuels and large-scale destruction of rain forests. Next year, 2008 has been proposed as the international year of the reef by Science magazine.
There are two problems, both of them serious. The addition of carbon dioxide and other greenhouse gases to the atmosphere has altered both the ocean's temperature and its acidity. Because most shallow-water corals exist near their temperature optimum, some are becoming heat-bleached.
The more problematic concomitant of climate change is that when carbon dioxide is absorbed by the oceans, as 30% of global industrial production is, it forms bicarbonate and hydrogen ions, which lower ocean pH and threaten the carbonate structure of the reef with dissolution. Since the industrial revolution, average ocean pH has been reduced by about 0.1 unit, and models predict further loss of 0.3 or 0.4 unit by the end of the century. Thomas Lovejoy, president of the H. John Heinz III Center for Science, Economics, and the Environment, calls it "the single most profound environmental change I've learned about in my entire career." In Australia, which has the best-managed reefs in the world, the Institute of Marine Science conducts continuous monitoring to document these changes.
Global warming is changing the temperature and acidity of the ocean at faster rates than happened at the end of the last ice age. If global warming and ocean acidification trends continue, coral reefs and many marine organisms, will not be able to adapt. The article is behind a subscriber firewall. I have reformatted a single paragraph in the article into three paragraphs and highlighted key phrases to make it easier to read.
We used global [CO2]atm and temperature data from the Vostok Ice Core study (5) to explore the ocean temperature and carbonate-ion concentration (10) seen today relative to the recent past for a typical low-latitude sea maintaining a mean temperature of 25°C during the past 420,000 years (Fig. 1B). The results show a tight cluster of points that oscillate (temperature ±3°C; carbonate-ion concentration ±35 µmol kg–1) between warmer interglacial periods that had lower carbonate concentrations to cooler glacial periods with higher carbonate concentrations. The overall range of values calculated for seawater pH is ±0.1 units (10, 11).
Critically, where coral reefs occur, carbonate-ion concentrations over the past 420,000 years have not fallen below 240 µmol kg–1. The trends in the Vostok ice core data have been verified by the EPICA study (6), which involves a similar range of temperatures and [CO2]atm values and hence extends the conclusions derived from the Vostok record to at least 740,000 years before the present (yr B.P.). Conditions today ([CO2]atm ~380 ppm) are significantly shifted to the right of the cluster points representing the past 420,000 years. Sea temperatures are warmer (+0.7°C), and pH (–0.1 pH units) and carbonate-ion concentrations (~210 µmol kg–1) lower than at any other time during the past 420,000 years (Fig. 1B). These conclusions match recent changes reported for measurements of ocean temperature, pH, and carbonate concentration (8). In addition to the absolute amount of change, the rate at which change occurs is critical to whether organisms and ecosystems will be able to adapt or accommodate to the new conditions (11).
Notably, rates of change in global temperature and [CO2]atm over the past century are 2 to 3 orders of magnitude higher than most of the changes seen in the past 420,000 years (Table 1). Rates of change under both low (B1) and high (A2) Intergovernmental Panel on Climate Change (IPCC) emission scenarios are even higher, as are recent measurements of the rate of change of [CO2]atm (9). The only possible exceptions are rare, short-lived spikes in temperature seen during periods such as the Younger Dryas Event (12,900 to 11,500 yr B.P.) (12). Given that recent and future rates of change dwarf even those of the ice age transitions, when biology at specific locations changed dramatically, it is likely that these changes will exceed the capacity of most organisms to adapt.
One sentence in this report in Science bears repeating and highlighting.
Given that recent and future rates of change dwarf even those of the ice age transitions, when biology at specific locations changed dramatically, it is likely that these changes will exceed the capacity of most organisms to adapt.
Over the past four hundred twenty thousand years the concentration of carbonate ion in sea water has always been above 240 micromoles per kilogram. Because of the huge amount of CO2 that has been dissolved into the upper ocean the concentration is now 210. Carbonate ion is necessary for forming aragonite, the mineral that forms reefs and shells for many marine organisms. When acidification causes ocean carbonate concentrations fall below a critical level, reef building and shell formation becomes impossible. Coral reef organisms will not able to adapt to the rapid changes we are causing if they continue at present rates. CO2 emissions must be greatly reduced to save marine ecosystems.
The authors of the article cautiously understate their case, as scientists usually do.
Conclusion
It is sobering to think that we have used the lower range of IPCC scenarios in our analysis yet still envisage serious if not devastating ramifications for coral reefs. Emission pathways that include higher [CO2]atm (600 to 1000 ppm) and global temperatures of 3° to 6°C defy consideration as credible alternatives. Equally important is the fact that IPCC scenarios are likely to be cautious given scientific reticence and the inherently conservative nature of consensus seeking within the IPCC process (53). Consequently, contemplating policies that result in [CO2]atm above 500 ppm appears extremely risky for coral reefs and the tens of millions of people who depend on them directly, even under the most optimistic circumstances.
Levels above 500ppm won't endanger just coral reefs. Marine organisms in the north Pacific and in the southern ocean are even more sensitive to CO2 increases because cold water temperatures increase the dissolution of CO2 and drive carbonate levels even lower than in the tropics.
Plans must be made now and implemented immediately to keep atmospheric carbon-dioxide levels below 500ppm to avoid a global marine catastrophe.