American research plan in cooperation with scientists in Canada and Mexico.

The CCSP plan begin with a strong focus on the problem of the “missing carbon sink” that must exist to account for the fact that much of the carbon being released into the atmosphere by human activities fails to show up as an increase in atmospheric CO2 concentration. There is a major policy interest in projecting the future capacity of the sink because it may strongly affect projections of the effects of future carbon emissions on climate. Most researchers have worked from two main hypotheses: that there is a large terrestrial carbon sink and that increases in oceanic carbon dioxide levels are also important to study.

The terrestrial carbon sink is believed to result from some combination of the following: (1) increased net primary productivity due to carbon and nitrogen fertilization from human activity and longer growing seasons associated with global warming; (2) decreases in the rate of disturbance of vegetation by fires; (3) recovery of vegetation from past disturbances (e.g., reforestation); and (4) other sources (including sediment burial in reservoirs, storage of carbon in wood products, and “pseudosinks” caused by transport of carbonaceous products such as food from one part of the world to another). Until recently, it was widely believed that the largest portion of the terrestrial sink was due to carbon dioxide fertilization of plants as a result of increased atmospheric carbon concentrations. Recent evidence is changing that view. Change in land cover due to human activity and the suppression of fires in the United States are now considered much more important than previously believed. In addition, a shift from open dumping of waste to landfilling and changes in agricultural management may also contribute significantly to the sink. Some of these changes involve only one-time and temporary increases in the sink, and some (such as fire suppression) may even be undergoing reversal. All these emerging understandings suggest that improved understanding of human actions on the land is critical for understanding the carbon sink and its future. Field’s assessment is that the CCSP’s research is addressing only about a third of the carbon sink in the United States (the portion due to carbon fertilization of plants) and that the rest must be understood by examining human activity.

Field noted several emerging issues in the understanding of carbon sinks:



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