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USGCRP Fiscal Year 2002 Accomplishments

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The following are some of the major accomplishments of the USGCRP's Carbon Cycle Science Initiative during Fiscal Year 2002:

Reconciled North American Carbon Sink Estimates:

For the first time, estimates of the carbon sink over North America were reconciled for a given time period (in this case, 1980-1989) using two distinct methods. In the past, atmospheric-based methods and land surveying methods did not give statistically similar estimates of the U.S. carbon sink. The methods and data sets used in this recent study pave the way for developing the capability to routinely quantify sources and sinks across North America and understand the underlying mechanisms. Enhancing our ability to estimate the quantity of CO2 absorbed by North American ecosystems will help hone estimates of atmospheric CO2 concentrations in future years.

A Large Carbon Sink in Northern Forests:

Significant biomass carbon gains in Eurasian and North American temperate forests and losses in some Canadian boreal forests have been revealed from analysis of two decades of AVHRR satellite data in combination with forest inventories. Increases in forest growth have been attributed to fire suppression and forest re-growth in the U.S. and declining harvests in Russia. Decreases in growth in Canada have been attributed to fires and infestations. This research suggests the possibility of surveying forests from space and will help in locating and characterizing the dynamics of terrestrial sinks and their role in sequestering carbon, and the impact of climate change on terrestrial ecosystems. We are now better able to track changes in global-scale terrestrial productivity, which is important for identifying where the carbon is being stored and where it is likely to continue to be stored.  

Figure 4.1.  North American terrestrial carbon sink: Contribution of increasing CO2 and climate to carbon storage by ecosystems in the United States
 

Agreement of Methodologies for Carbon Uptake Measurement:

AmeriFlux research quantified net carbon uptake by a forest ecosystem using two independent measures. Over a 10-year period at the same site at the Harvard Forest, estimates of carbon uptake from both flux tower measurements and intensive forest inventory measurements and biometry were found to be statistically similar. Close agreement of the measures builds confidence in the use of the two different methods for more accurately estimating net ecosystem production and terrestrial carbon sinks.

Insight into Carbon Exchange Using Oxygen Isotope:

Researchers have developed a model that simulates the flow of the oxygen-18 isotope in CO2 and water between plants, soil, and canopy water vapor. The oxygen-18 isotope acts as a tracer that allows scientists to partition the sources of CO2 and water, thus providing significant insight into the properties governing the carbon exchange between ecosystems and the atmosphere. The model has been incorporated into the NCAR Community Climate System Model (CCSM) -- a linked land-surface model. This modification provides a new and powerful tool for providing information on carbon fluxes in the plant and soil components of ecosystems. This research is necessary for understanding and interpreting larger-scale regional and continental fluxes, and for understanding and predicting the behavior of terrestrial carbon sinks.

Identification of Carbon Management Options:

At the Forestry and Agriculture Greenhouse Gas Modeling Forum in 2001, two USGCRP agencies convened leading researchers to compare potential greenhouse gas mitigation options in the agriculture and forestry sectors. At this first of what is intended to be a series of annual workshops, attendees compiled and compared North American agriculture and forestry emission-reduction estimates across selected global and national models that link economic and biophysical analyses and identified promising directions for future research to inform decisionmaking about management options.

Synthesis and Collaboration of Carbon Knowledge:

The Forest Service led an international, multiagency meeting on carbon dynamics in urban, rangeland, forest, agricultural and wetland ecosystems. The proceedings (published in a special issue of the Journal of Environmental Pollution ) summarized current understanding of carbon stocks and carbon dynamics in terrestrial systems. The proceedings included numerous papers that emphasized the importance of understanding the roles of disturbances (such as fire), climate, basic ecological processes, and management practices to accurately model and project carbon sequestration potential in different regions and ecosystems. This knowledge synthesis documents the "state-of-the-science" to support: (1) increasing carbon sequestration; (2) monitoring and verifying changes in carbon sequestration; and (3) developing accounting rules and guidelines for potential decisionmaking on reporting and trading of future carbon credits.

Estimation of Anthropogenic CO2 Uptake in Pacific Ocean:

The first comprehensive ocean inventories of anthropogenic carbon storage are nearing completion in the Pacific and Atlantic Oceans. Using database methods, the Pacific Ocean was found to carry a burden of anthropogenic carbon that is approximately 45 billion tons greater than in preindustrial times, in agreement with ocean modeling simulations. This represents about 20 percent of the total fossil fuel emissions over the period. A complete synthesis of ocean inventories based upon direct measurements has recently been published. These basin-wide inventories have contributed to our understanding of how much carbon emitted by humans is absorbed by the ocean, as well as how anthropogenic carbon is transported and distributed among the Earth's major ocean basins.

Air-Sea CO2 Exchange:

The first study of direct air-sea exchange of carbon dioxide in the equatorial Pacific Ocean was completed in 2001.This region is the largest natural oceanic source of carbon dioxide to the atmosphere. The kinetics of gas exchange (between the air and sea is currently a major source of uncertainty in quantifying ocean uptake at regional scales. Direct measurements of air-sea CO2 exchange were accurately obtained using three distinct methodologies. These data will be incorporated into algorithms to improve estimates of ocean uptake of fossil-fuel-derived carbon dioxide.

Figure 4.2  Carbon Dioxide Measurements and Experiments -- (a) AmeriFlux tower; (b) Free Air CO2 Enrichment (FACE); (c) Elevated CO2 concentration experiment

Interannual and Climate-Driven Variation in Ocean Biomass Observed:

Based on three years of data from the SeaWiFS ocean color satellite instrument, the first continuous global estimates of ocean plant biomass and terrestrial plant photosynthesis that accurately track and characterize seasonal and interannual variability were documented. Strong El Niño/La Niña-related differences were observed, especially in the tropical oceans where significant increases in ocean plant biomass were observed. In addition, the first successful cross-calibration of two ocean-color data sets -- from SeaWiFS and Japan's Ocean Color and Temperature Scanner (OCTS) -- was completed, initiating a long-term, highly calibrated ocean color time series for the global ocean. The ability to quantify annual and interannual changes in ocean and land plant productivity will enhance our ability to forecast ecological responses to changes in climate.