Study: People’s Carbon Pollution Not Only Changing the Atmosphere But Also the Oceans

Written by Lisa Hayden on . Posted in Learn


A new study concludes that human-generated carbon pollution over the last 100 to 200 years has rapidly and dramatically changed the chemistry of the oceans – a process likely to intensify in the coming century at great risk to the world’s coral reefs.

Using computer modeling of Earth’s climate and oceans along with direct observations over the past 30 years, an international team of scientists, including The Nature Conservancy’s own marine scientist Elizabeth McLeod, found that carbon dioxide emissions from the past two centuries have raised the ocean’s acidity far beyond the natural variations of the last 21,000 years.

Published in the Jan. 22 online edition of the journal Nature Climate Change, the study was led by researchers at the International Pacific Research Center, University of Hawaii at Manoa, and co-funded by The Nature Conservancy and the Japan Agency for Marine-Earth Science and Technology.

Scientists know that nearly one-third of the carbon pollution created from people’s activities is absorbed by the oceans. When this carbon dioxide reacts with sea water, the ocean becomes more acidic. And with rising acidity, the more difficult it becomes for ocean life such as mollusks, plankton and corals to produce shells or skeletons from calcium carbonate (a process known as calcification).

To visualize the acidification from 1800 to the present, and to look ahead to 2100, check out the animation above, prepared by lead author Tobias Friedrich. The spreading orange/red zones indicate lower saturations of aragonite (a form of calcium carbonate needed by marine life) on the ocean’s surface as acidification increases — a widely used indicator of the process. 

What does all this mean for brightly colored coral reefs— so important not only to tourists and divers — but as a source of medicines, and as shelter for fish and sea life that provide protein for many people of island and coastal communities?

“Our results suggest that severe reductions are likely to occur in coral reef diversity, structural complexity and resilience by the middle of this century,” says co‐author Professor Axel Timmermann.

The study indicates that corals are currently found in about half of the oceans, mostly in the tropics – areas with adequate levels of aragonite. But these zones are expected to continue shrinking, with Hawaii, the Caribbean and the western Pacific likely to be vulnerable to acidification. Though some regions seem to be more resilient to man-made influences on ocean chemistry, the study predicts that continued use of fossil fuels may leave only about 5 percent of the oceans hospitable to corals by 2100. 

“When Earth started to warm 17,000 years ago, terminating the last glacial period, atmospheric CO2 levels rose from 190 parts per million (ppm) to 280 ppm over 6,000 years. Marine ecosystems had ample time to adjust,” researcher Friedrich explains. “Now, for a similar rise in CO2 concentration, to the present level of 392 ppm, the adjustment time is reduced to only 100 – 200 years.”

Previous research by Conservancy scientist McLeod includes study of so-called “blue carbon,” or the important role of coastal ecosystems such as mangroves, sea grasses and salt marshes in storing carbon dioxide.

Through the Reef Resilience Initiative, the Conservancy works to identify the healthiest reefs and protect them from damage, so they can better withstand climate impacts. Click here to hear learn more about the Conservancy’s work to protect corals.

Lisa Hayden is a blogger and writer for The Nature Conservancy

Photo 1: © Rod Salm (Healthy corals, Komodo National Park, Indonesia).

Thumbnail, Photo 2: © J.E. Maragos (Coral gardens in reef pool, Palmyra Atoll).

Animation by Tobias Friedrich 2012, International Pacific Research Center. (Spreading orange/red zones indicate lower saturations of aragonite (a form of calcium carbonate needed by marine life) on the ocean’s surface as sea water becomes more acidic — a widely used measure of ocean acidification. The animation shows how aragonite saturation is projected to decrease towards the end of the 21st century as man-made carbon dioxide accumulation in the atmosphere continues to rise.)

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