The ecological and economic consequences are difficult to predict but possibly calamitous, warn a team of chemical oceanographers in the July 4 issue of Science, and halting the changes already underway will likely require even steeper cuts in carbon emissions than those currently proposed to curb climate change.
Ken Caldeira of the Carnegie Institution's Department of Global Ecology, writing with lead author Richard Zeebe of the University of Hawaii and two co-authors*, note that the oceans have absorbed about 40% of the carbon dioxide (CO2) emitted by humans over the past two centuries. This has slowed global warming, but at a serious cost: the extra carbon dioxide has caused the ocean's average surface pH (a measure of water's acidity) to shift by about 0.1 unit from pre-industrial levels. Depending on the rate and magnitude of future emissions, the ocean's pH could drop by as much as 0.35 units by the mid-21st century.
This acidification can damage marine organisms. Experiments have shown that changes of as little as 0.2-0.3 units can hamper the ability of key marine organisms such as corals and some plankton to calcify their skeletons, which are built from pH-sensitive carbonate minerals. Large areas of the ocean are in danger of exceeding these levels of pH change by mid-century, including reef habitats such as Australia's Great Barrier Reef.
Most marine organisms live in the ocean's sunlit surface waters, which are also the waters most vulnerable to CO2-induced acidification over the next century as emissions continue. To prevent the pH of surface waters from declining more than 0.2 units, the current limit set by the U.S. Environmental Protection Agency in 1976, carbon dioxide emissions would have to be reduced immediately.
"In contrast to climate model predictions, such future ocean chemistry projections are largely model-independent on a time scale of a few centuries," the authors write, "mainly because the chemistry of CO2 in seawater is well known and changes in surface ocean carbonate chemistry closely track changes in atmospheric CO2."
Although the ocean's chemical response to higher carbon dioxide levels is relatively predictable, the biological response is more uncertain. The ocean's pH and carbonate chemistry has been remarkably stable for millions of years--much more stable than temperature.
"We know that ocean acidification will damage corals and other organisms, but there's just no experimental data on how most species might be affected," says Caldeira. "Most experiments have been done in the lab with just a few individuals. While the results are alarming, it's nearly impossible to predict how this unprecedented acidification will affect entire ecosystems." Reduced calcification will surely hurt shellfish such as oysters and mussels, with big effects on commercial fisheries. Other organisms may flourish in the new conditions, but this may include undesirable "weedy" species or disease organisms.
Though most of the scientific and public focus has been on the climate impacts of human carbon emissions, ocean acidification is as imminent and potentially severe a crisis, the authors argue.
"We need to consider ocean chemistry effects, and not just the climate effects, of CO2 emissions. That means we need to work much harder to decrease CO2 emissions," says Caldeira. "While a doubling of atmospheric CO2 may seem a realistic target for climate goals, such a level may mean the end of coral reefs and other valuable marine resources."
* James Zachos, University of California, Santa Cruz, and Toby Tyrrell, Southampton University, U.K.
Carnegie Institution (2008, July 6). Acidifying Oceans Add Urgency To Carbon Dioxide Cuts. ScienceDaily. Retrieved July 6, 2008, from http://www.sciencedaily.com /releases/2008/07/080703140716.htm
Posts
2 comments:
Message I found in a bottle...
The report on my imminent death is premature. I have been sloshing around in the basins on the crust for more than four billion years. I now cover nearly 71 per cent of the planet. Since the last ice age I have lifted myself out of the basin by 120 metres and scared the tribes of Noah to the higher ground. During deep time, I became the universal solvent for the volcanoes and the clouds. I have taken up as much salt as required by local circumstances and sometimes give it back in hot shallows and desert areas of my world. I have given man the salt in his blood. Your CO2 output is infinitesimally small. I have absorbed as much gas as I need to maintain balance with the organic world within me and on land. The exchange is so peaceful that science calls it equilibrium. I can absorb more CO2, if the plants do not need it, and it does not give me acid imbalance. My pH will remain basic no matter what you say. The variations you measure have come and gone many uncountable times on the planet and your baseline is too small to know the truth. What you do not get is that warming of the oceans releases CO2 and other gasses from my water, while cooling my water allows me to take up CO2 in vast amounts to nestle with the other molecules in my coldest most remote realms. I can absorb all that man can produce because your impact is feeble compared to my capacity.
Please watch me with humility for you cannot change me. I am the ongoing sink for the planet, and I am huge and my heat content is beyond your estimation. Measure me here and there with your microscopes but know that I will never be that way in that place again. Open your mind to the infinite cycles of chemistry and physics and kneel on my beach. You can only hurt me by not respecting my infinite ability to change chemistry and temperature in all the corners of the seas. My CO2 feeds your plants and your plants provide all the oxygen you breathe. Your base line is infinitesimally small yet your mouth is wide open. Please stop sending me your plastic bottles.
Poseidon
Yeah, right.
Post a Comment