Co2 Sequestration

One of the key issues in global warming and one in which the ocean plays a significant role, as illustrated earlier, is the storage of CO2. Long-term sequestration of carbon dioxide in the ocean waters directly affects the amount of CO2 in the atmosphere by providing a reservoir that balances out the overloading of CO2 into the atmosphere by humans. The key research questions here are how much CO2 the oceans can effectively store, how long it takes to store it, whether the storage is permanent, and what effect the CO2 may have on marine ecosystems.

According to a study by Adina Paytan, an oceanographer at the University of California at Santa Cruz, the last time Earth experienced an extreme global warming event, the oceans acted as a buffer and helped slow the warming process. Her research indicates that during the period of Earth's history referred to as the Paleocene-Eocene thermal maximum (PETM), 55 million years ago, ocean plant life produc tivity increased and served as a mechanism to capture excessive carbon from the atmosphere. The plant life eventually settled to the ocean floor where it was buried—effectively sequestering the CO2. Paytan stresses that the mechanism was increased productivity and not just changes in ocean chemistry, as others had proposed.

According to Paytan, when the plant matter settles at the bottom of the ocean, it contains barite (barium sulfate) in its tissues. When the barium reaches its saturation point on the ocean floor, it combines with sulfur and forms the mineral barite. Paytan believes it may have been this sequestration process that eventually brought down the warmer Earth temperatures and suggests that the same process may play an important role today in Earth's adjustment to global warming. The major drawback, she cautions, is that it is a slow, natural process—much slower than the current human-caused buildup of carbon occurring today. She determined that the barite accumulation in the PETM took 170,000 years, illustrating that it is a lot easier to heat up Earth than to cool it down again.

Another theory surrounding the events of the PETM has been proposed by the scientists at NASA's GISS. According to Gavin Schmidt there, large quantities of CO2 were stored in a reservoir of methane hydrate deposits buried on the continental shelves of the oceans. Methane hydrates are formed when bacteria decompose organic matter. During the process, bacteria produce methane, and in cold, high-pressure environments, methane hydrates are formed.

Another study, conducted by British scientists that appeared in the November 2007 edition of the Journal of Geophysical Research, has suggested that the world's oceans—which scientists believe is a tremendous reservoir for the CO2 being added to the atmosphere—are beginning to lose their ability to absorb CO2 from the atmosphere. According to data they collected, the North Atlantic's absorption of CO2 dropped in half between 1995 and 2005.

These researchers warn that if the ocean loses its ability to absorb CO2, it will increase the effects of global warming felt on land. Through their research it was also determined that the oceans were becoming more acidic because of the CO2 uptake in the ocean. This presents a compound problem: If the oceans stop absorbing as much CO2, then the negative effects of global warming will increase; if the oceans absorb more CO2, the oceans become more acidic, which is harmful for marine ecosystems and biodiversity.

Some scientists warn to be cautious about making assumptions concerning findings, stating it is still too early to make concrete conclusions. How much is natural variation and how much is anthropogenic still needs to be determined. What is stressed, however, is that the ocean's function as a CO2 "sink" can change quickly and needs to be monitored closely for subtle changes that may offer clues to long-term climate change and global warming.

In another study, whose results were published in the Proceedings of the National Academy of Sciences, it was determined that economic growth had caused levels of atmospheric CO2 to increase 35 percent faster since 2000 than had been expected. Pep Canadell of the Global Carbon Project attributed this increase to an 18 percent decline in the efficiency of CO2 sinks (the world's oceans and forests), laying the rest of the blame on the increased use of fossil fuels.

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