Ocean acidification: The other climate change story

In the decades and century to come, we will experience extraordinary changes in our world’s oceans and atmosphere, with consequences that may dramatically change the way we live our lives.

Perhaps the greatest challenge for mankind is climate change. We often think of climate change as global warming, but I think Thomas Friedman said it best in Hot, Flat, and Crowded, when he called it “global weirding.” Climate change will bring changes in atmospheric and oceanic temperature, weather patterns including winds, precipitation and drought, and even the chemistry of our oceans.

Marine life, from microscopic life forms at the bottom of the food web to larger species such as coral, shellfish, and commercial fisheries, will be affected by a phenomenon called “ocean acidification.” Commercial fisheries, already failing, may suffer further economic loss. NOAA researchers are at the forefront of studying and monitoring this marker of climate change. Currently, a lone buoy equipped with sensors measures the extent of acidification in the Gulf of Alaska. More and better sensors, technologies for studying impacts on physiology and ecosystems, and modeling efforts to provide ecological models, projections, and forecasts, will help us better understand our changing ocean.

For this first blog, I’ve asked one of our NOAA researchers, Dr. Richard Feely, to tell us more about “ocean acidification.” Dr. Feely recently was featured in the film, “A Sea Change: Imagine a World without Fish.”

Ocean Acidification Along the West Coast of North America

Richard A. Feely

Ever since the beginning of the industrial revolution the release of carbon dioxide (CO2) from our industrial and agricultural activities has resulted in an increase in atmospheric CO2 concentrations from approximately 280 to 387 parts per million (ppm). The atmospheric concentration of CO2 is now higher than experienced on Earth for at least the last 800,000 years, and is expected to continue to rise at an increasing rate, leading to significant temperature increases in the atmosphere and the ocean surface in the coming decades. During this time, the ocean has absorbed more than 528 billion tons of carbon dioxide from the atmosphere, or about one-third of anthropogenic (human caused) carbon emissions.

This absorption of CO2 from the atmosphere has benefited humankind by significantly reducing greenhouse gas levels in the atmosphere, thereby partly minimizing global warming. However, when the anthropogenic CO2 is absorbed by seawater, chemical changes occur that reduce both seawater pH and the concentration of carbonate ion, in a process commonly referred to as ocean acidification. As a result, the acidity of ocean surface waters has already increased by about 30% since the beginning of the industrial revolution. It now appears likely that the level of CO2 in the atmosphere might double over its pre-industrial levels by the middle of this century. This rapid change in ocean chemistry is more dramatic than at any time in the past 20 million years. The pH decrease will lead to a reduction in the saturation state of seawater with respect to aragonite and calcite, which are the two most common types of calcium carbonate formed by marine organisms. These changes in seawater chemistry will have negative consequences for a wide variety of marine calcifiers, such as clams, oysters, mussels, abalone, sea urchins, and corals.

On the west coast of North America, the seasonal upwelling of subsurface waters along the coast brings CO2-enriched waters onto the shelf and, in some instances, into the surface ocean. It appears that this water, in addition to its original high level of CO2 resulting from natural respiration processes in the subsurface layers, is also significantly contaminated with anthropogenic CO2 as it was last in contact with the atmosphere about 50 years ago. An immediate consequence of this additional CO2 is that the CO2 concentrations in these upwelled waters will be significantly greater than they would have been in pre-industrial times. Furthermore, each ensuing year will draw on water that has been exposed to the atmosphere still more recently, resulting in yet higher CO2 levels. Since these “ocean-acidified” upwelled waters are already corrosive with respect to aragonite they are a potential threat to many of the calcifying aragonitic species that live along our coasts.

On a global scale, the most acute impacts of ocean acidification can be avoided if average atmospheric CO2 concentrations are kept below about 550 ppm. Even at this concentration, there are likely to be significant local impacts in upwelling or high-latitude regions. If atmospheric CO2 concentrations continue to increase above this level, the severity and extent of the biological impacts will increase dramatically, with large portions of open-ocean and coastal regions becoming increasingly corrosive to marine calcifiers over time. Increased ocean acidification with increasing CO2 emissions is a certainty, but the impact on ocean biology and the value of the ecosystem services for mankind that a future low pH ocean will sustain is less certain. In order to ensure that atmospheric CO2 concentrations stay below 550 ppm, the current increase in total CO2 emissions must be eliminated within about 10-12 years.

Dr. Richard Spinrad, Year of Science 2009, 24 June 2009. Article.

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