What are the links between ocean acidity, ocean temperature and elevated atmospheric CO2? What are the implications of increasing ocean acidity in the upper ocean to ecosystems and to society? Is there historical evidence of increased ocean acidity associated with warmer temperatures and higher levels of oceanic and atmospheric CO2? If so, what were the consequences? Are there options for keeping ocean acidity in check? Is the increase in ocean acidity independent of any climate warming resulting from the buildup of CO2?
Moderator: Dr. Anthony Socci, Senior Policy Fellow
Dr. Richard A. Feely, Supervisory Oceanographer, NOAA Pacific Marine Environmental Laboratory, Seattle, WA
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Dr. Kenneth Caldeira, Department of Global Ecology, Carnegie Institution, Stanford University, CA
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Atmospheric Carbon Dioxide, Ocean Acidity
and Biology - Context and Basics:
Carbon dioxide is one of the most important gases in the atmosphere affecting the radiative heat balance of the earth. For 400,000 years prior to the industrial revolution, atmospheric CO2 concentrations remained between 200 to 280 parts per million (ppm). As a result of the industrial and agricultural activities of humans, current atmospheric CO2 concentrations are around 380 ppm, increasing at about 1% per year. Over the past two decades, only half of the CO2 released by human activity has remained in the atmosphere; about 30% has been taken up by the ocean and 20% by the terrestrial biosphere. The atmospheric concentration of carbon dioxide is now higher than experienced on Earth for at least the last 400,000 years, and is expected to continue to rise, leading to significant temperature increases by the end of this century. The global oceans are the largest natural reservoir for this excess carbon dioxide, absorbing approximately one-third of the carbon dioxide added to the atmosphere by human activities each year, and over the next millennium, is expected to absorb approximately 90% of the CO2 emitted to the atmosphere. It is now well established that there is a strong possibility that dissolved CO2 in the ocean surface will double over its pre-industrial value by the middle of this century, with accompanying surface ocean acidity (pH) and carbonate ion (CO3-2) decreases that are greater than those experienced during the transition from ice ages to warm ages.
Impacts of Anthropogenic CO2 on Ocean Chemistry
The uptake of anthropogenic CO2 by the ocean changes the chemistry of the oceans and can potentially have significant impacts on the biological systems in the upper oceans. Estimates of future atmospheric and oceanic CO2 concentrations, based on the Intergovernmental Panel on Climate Change (IPCC) emission scenarios and general circulation models indicate that by middle of this century atmospheric CO2 levels could be reach over 500 ppm, and near the end of the century they could be over 800 ppm. Corresponding models for the oceans indicate that the surface water acidity (pH) drop (increased acidity) would be approximately 0.4 pH units, and the carbonate ion concentration would decrease almost 50 % by the end of the century. This surface ocean pH drop would be lower than it has been for more than twenty million years. A pH reduction of approximately 0.1 unit in surface waters has occurred already due to oceanic uptake of anthropogenic CO2.
Ecological Impacts of Changing CO2 on Marine Organisms
Recent field and laboratory studies reveal that the carbonate chemistry of seawater has a profound negative impact on calcification rates (rates of shell and skeletal production) of individual species and communities in both planktonic (floating) and ocean bottom organisms. The calcification rate of nearly all calcium-secreting organisms investigated to date decreased in response to decreased carbonate ion concentration. This response holds across multiple taxonomic groups from single-celled organisms to reef-building corals. In general, when dissolved CO2 was increased to two times pre-industrial levels, a decrease in the calcification rate was observed, ranging from -5 to -50%. For example, decreased carbonate ion concentration has been shown to significantly reduce the ability of reef-building corals to produce their calcium carbonate skeletons, affecting growth of individual corals and the ability of the larger reef to maintain a positive balance between reef building and reef dissolution. Scientists have also seen a reduced ability to produce protective calcium carbonate shells in species of marine algae and planktonic molluscs, on which other marine organisms feed. Calcification probably serves multiple functions in calcifying organisms. Decreased calcification would presumably compromise the fitness or success of these organisms and could shift the competitive advantage towards non-calcifiers. Carbonate skeletal structures are likely to be weaker and more susceptible to dissolution and erosion. While long-term consequences are unknown, experimental results from enclosed laboratory experiments indicate that coral reef organisms do not acclimate to decreasing carbonate saturation states over several years. Thus, if calcifying organisms cannot adapt to the changes in seawater chemistry that will occur, the geographical range of some species may be reduced or may shift latitudinally in response to rising CO2. Based on the best available understanding, it appears that as levels of dissolved CO2 in sea water rise, the skeletal growth rates of calcium-secreting organisms will be reduced as a result of the effects of dissolved CO2 on ocean acidity and consequently, on calcification. The effects of decreased calcification in microscopic algae and animals could impact marine food webs and, combined with other climatic changes in salinity, temperature, and upwelled nutrients, could substantially alter the biodiversity and productivity of the ocean. As humans continue along the path of unintended CO2 sequestration in the surface oceans, the impacts on marine ecosystems will be direct and profound.
Increasing Ocean Acidity as a Consequence of the Buildup of Atmospheric CO2 - Implications for the Present and the Future:
Ocean acidification (ocean chemistry change) is a highly predictable consequence of increased atmospheric carbon dioxide concentrations. Surface ocean chemistry changes resulting from changes in atmospheric composition can be predicted with a high degree of confidence.
Ocean acidification means that there would be concern over carbon dioxide emissions independently and apart from any possible effects of carbon dioxide on the climate system. Ocean acidification and climate change are both effects of CO2 emissions to the atmosphere, but they are completely different; ocean acidification depends on the chemistry of carbon dioxide whereas climate change depends on the physics of carbon dioxide.
If current trends in carbon dioxide emissions continue, the ocean will acidify to an extent and at rates that have not occurred for tens of millions of years. There is some uncertainty both in the relationship between carbon dioxide emissions and future atmospheric concentrations and in inferred past ocean chemistry, but these uncertainties do not throw into doubt the fact that we are producing highly unusual chemical conditions in the world's oceans. Right now, ocean chemistry is changing at least 100 times more rapidly than it has changed in the 100,000 years preceding our industrial era.
Ocean acidification of these amounts and at these rates could be expected to have major negative impacts on corals and other marine organisms that build their shells or skeletons out of carbonate minerals. When carbon dioxide is absorbed by the ocean it forms carbonic acid. Carbonic acid is corrosive to carbonate minerals. The impact on other categories of marine organisms is less clear, but there is likely to be disruptions through the entire marine food chain. The potential for ecological or micro-evolutionary adaptation is unclear at this time; however, both in today's ocean and over geologic time the rate of accumulation of shells and skeletons made from carbonate minerals shows a consistent relationship with ocean chemical conditions indicating that the success of these organisms is largely controlled by marine chemistry.
The only practical way to avoid the risk of major damage to the global marine environment is to reduce the emissions of carbon dioxide to the atmosphere. A major effort would be required, but it appears technologically feasible to diminish CO2 emissions in an economy that is growing vigorously (The President's Climate Change Technology Program is aimed at achieving this goal.). Other mitigation approaches might be applicable at small scales (say to preserve a few individual corals in a marine park), but these approaches are unlikely to be feasible on a large scale.
Research is needed to better understand the vulnerabilities, resilience, and adaptability of marine organisms and ecosystems. The science of understanding the biological consequences of ocean acidification, and placing these changes in a historical context, is in its infancy; initial information indicates that there is cause for great concern over the threat carbon dioxide poses for the health of our oceans.
Dr. Richard A. Feely is a Supervisory Oceanographer at the NOAA Pacific Marine Environmental Laboratory in Seattle. He also holds an affiliate professor faculty position at the University of Washington School of Oceanography. His major research areas are carbon cycling in the oceans and hydrothermal processes at mid-ocean ridges. He received a B.A. in chemistry from the University of St. Thomas, in St Paul, Minnesota in 1969. He then went onto Texas A&M University where he received both an M.S degree in 1971 and a Ph.D. degree in 1974. Both of his post-graduate degrees were in chemical oceanography. He is the co-chair of the U.S. CLIVAR/CO2 Repeat Hydrography Program. He is also a member of the U.S. science steering committees for the U.S. Carbon Cycle Science Program, the U.S. Ocean Carbon and Climate Change Program, and the U.S. Carbon and Biochemistry Program. He is a member of the American Geophysical Union, The American Association for the Advancement of Science and The Oceanography Society. Dr. Feely has authored more than 150 refereed research publications.
Dr. Ken Caldeira has been engaged in a range of research relating to climate, the carbon cycle, oceanography, and energy systems. He acted as a technical advisor to the US delegation on technological options to mitigate climate change in preparation for the recent G8 summit in Gleneagles, Scotland. Prior to joining the Carnegie Institution’s Department of Global Ecology on the Stanford campus in July of this year, Ken Caldeira worked in the Energy and Environment Directorate of Lawrence Livermore National Laboratory for more than a decade.
Dr. Caldeira’s recent publications relate primarily to ocean chemistry change, climate change, and energy systems. Some of this recent research has led to the conclusion that continued fossil fuel burning and associated atmospheric CO2 release may make the ocean more acidic than it has been for millions of years (Caldeira and Wickett, Nature, 2003), with far-reaching implications. A brief survey of Dr. Caldeira’s recent publications include the following: "A portfolio of carbon management options," published by the Scientific Committee on Problems in the Environment (SCOPE, 2004); an overview on energy and climate in the Encyclopedia of Energy; a study on how the evolution of calcareous plankton may have helped to stabilize Earth's climate (Ridgwell et al, Science, 2003); a National Academy of Engineering study of the effectiveness and unintended consequences of ocean fertilization as a carbon sequestration strategy; a study of the implications of uncertainty in climate sensitivity to increased atmospheric CO2 on predictions of future demand for carbon-emissions-free energy (Caldeira et al., Science, 2003); a study on geoengineering Earth's radiation balance to mitigate climate change (Govindasamy et al., 2003); a study of the economics of carbon sequestration in leaky reservoirs (Herzog et al, 2003); and a study of the effect of model resolution on simulations of ocean sequestration and CFC uptake (Wickett et al., 2003).
Dr. Caldeira also serves as a Coordinating Lead Author for the oceans chapter of the upcoming IPCC Special Report on CO2 Capture and Storage, and Lead Author for the “State of the Carbon Cycle”, Synthesis and Assessment Product. He has served on the US Global Carbon Cycle Scientific Steering Group, the UNESCO/International Oceanography Commission CO2 Panel of Experts, and the Meetings Committee of the American Geophysical Union.
Dr. Caldeira received his Ph.D. in Atmospheric Sciences from New York University in 1991, an MS degree in Atmospheric Sciences from NYU, and a BA degree in Philosophy from Rutgers College.
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