Acidifying oceans add urgency to CO2 cuts

July 3, 2008

It's not just about climate change anymore. Besides loading the atmosphere with heat-trapping greenhouse gases, human emissions of carbon dioxide have also begun to alter the chemistry of the ocean—often called the cradle of life on Earth. 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."

Source: Carnegie Institution

Explore further: Acid attack—can mussels hang on for much longer?

Related Stories

Acid attack—can mussels hang on for much longer?

July 5, 2016

Scientists from The University of Washington have found evidence that ocean acidification caused by carbon emissions can prevent mussels attaching themselves to rocks and other substrates, making them easy targets for predators ...

Growing Arctic carbon emissions could go unobserved

June 28, 2016

A new NASA-led study has found that in at least part of the Arctic, scientists are not doing as good a job of detecting changes in carbon dioxide during the long, dark winter months as they are at monitoring changes during ...

Recommended for you

Historical records miss a fifth of global warming: NASA

July 22, 2016

A new NASA-led study finds that almost one-fifth of the global warming that has occurred in the past 150 years has been missed by historical records due to quirks in how global temperatures were recorded. The study explains ...

2016 climate trends continue to break records

July 19, 2016

Two key climate change indicators—global surface temperatures and Arctic sea ice extent—have broken numerous records through the first half of 2016, according to NASA analyses of ground-based observations and satellite ...

Warmer Mediterranean turns the Sahel green

July 21, 2016

Climate change can have mixed consequences: It would appear that the warming of the Mediterranean region, which has brought greater heat and drought to the countries there for around 20 years, is behind an increase in rainfall ...

6 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

tpb
2.4 / 5 (9) Jul 03, 2008
How did coral survive in the past when CO2 levels were more than 10 time as high as now?
Captain_Sakonna
2.7 / 5 (7) Jul 03, 2008
When was that tpb?

I don't understand the hysteria--the article says that some organisms will be hurt, but others might flourish. Yes, this might include undesirable species, but why focus on the bad when there might be just as much good? It seems to me that we need to know more about how ocean acidification will affect these ecosystems before we jump to conclusions.
gopher65
3.9 / 5 (7) Jul 03, 2008
I just hope that the particular species of algae which supplies 50-90% of the atmospheric oxygen isn't one of the ones that dies:P. Don't mass extinctions follow in the footsteps of large CO2 releases? (which *follows* from periods of warming, rather than preceding it)
mikiwud
2 / 5 (4) Jul 05, 2008
gopher65,
these particular algae rely on CO2 to exist,oxygen is just, fortunately for us, a byproduct.
BTW,the oceans are not acidic,they alkaline,therefore are getting (if anything at all)less alkaline not more acidic,but it carries more impact for the scaremongers to put it the other way.They only become acidic when the Ph value drops below 7 (neutal),and there is not enough CO2 if ALL fossil fuels were burnt to cause that.
GrayMouser
2.5 / 5 (2) Jul 10, 2008
Considering that there are areas of the ocean that have been undergoing long term release of CO2 from the sea bed (see http://www.jennif...20.html) without harm, I don't see what the fuss is about.
dachpyarvile
1 / 5 (1) Jun 09, 2009
Colder water dissolves more CO2. Warmer water does not. Ergo, the waters are cooling, which is consistent with the data I have been observing over the last four years now.

Fishing regulations influenced by the greenies are the real causes of job loss.

In addition, we do not have to worry about the algae. Growth and proliferation is on the increase because algae love areas high in CO2.

The article is pure propaganda.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.