Meetings and Events
Global Carbon Cycle Program Principal Investigators Meeting
Hilton Washington D.C./Silver Spring
10-11 September 2007
Southern Ocean Gas Exchange Experiment (GasEx) Meeting
Hilton Washington D.C./Silver Spring
12 September 2007
Description
The Climate Program Office's Global Carbon Cycle (GCC) program seeks to improve our ability to predict the fate of
anthropogenic carbon dioxide (CO
2) and future atmospheric CO
2 concentrations
using a combination of atmospheric and oceanic global observations, process-oriented field
studies and modeling.
GCC research is integrated across four over-riding themes:
Global Location, Magnitude and Dynamics of Carbon Sources and Sinks
A variety of atmospheric, oceanic and terrestrial data has shown that both the ocean and
terrestrial biosphere currently take up and store a significant portion of the carbon released
to the atmosphere as a result of human activities. Preliminary progress has been made on
locating sources and sinks of carbon on a regional basis and characterizing their magnitude
and behavior over time. The results obtained thus far are at the limit of detection, however,
and cannot be extended to many regions of the world due to lack of data. Optimization studies
have suggested a few key terrestrial regions in which to locate additional sampling stations.
In addition, large areas of the oceans are currently vastly undersampled for the purposes of
quantifying regional oceanic source and sink magnitude and variability. Improvements in
sampling technology, spatial coverage, process parameterizations and transport models will
greatly improve our characterization of global carbon sources and sinks by region.
Northern Hemisphere Carbon Sinks
Atmospheric and oceanic data and models have predicted that the terrestrial sink is larger
in the Northern Hemisphere than in the Southern Hemisphere. Recent studies have suggested that
a large portion of this terrestrial sink may be located in North America for the period 1988-1992,
although there is considerable debate concerning the magnitude and mechanism for this sink. The
initial focus of this research theme is to constrain estimates of the Northern Hemisphere
terrestrial sink and identify responsible mechanisms using a combination of field experiments,
observations, and models.
Causes of Variability in Sources and Sinks
The rate of increase of carbon dioxide in the atmosphere can vary significantly on
interannual and decadal time-scales. The causes of this variability are unknown: while a
small amount is a result of variations in emissions, the majority is due to variability in
uptake by the oceans and terrestrial biosphere. Several factors have been hypothesized to
control this variability, including climate modes such as El Nino-Southern Oscillation,
historical and current land use, and CO2 and N fertilization. Studies are needed
which investigate how various factors influence global carbon cycle variability over a variety
of temporal scales, and identify which factors are the most important.
Future Atmospheric Carbon Dioxide Concentrations
Current models used to project future atmospheric carbon dioxide concentrations assume that
the carbon cycle will continue to operate in the same way it has operated in the recent past.
These models do not take into account the limitations of the carbon sink on land, or how
biological, chemical and physical processes in the ocean and land might change either due to
natural variability or external forcing. For example, it has been suggested that long-term
uptake and storage of carbon by the ocean may be reduced by climate change, resulting in an
increased proportion of carbon dioxide remaining the atmosphere. By examining the carbon cycle
as an integrated system, identifying how it interacts with climate and other influences such as
land use patterns, and incorporating the carbon cycle into dynamic earth system models, more
realistic predictions of future atmospheric carbon dioxide concentrations and potential abrupt
changes in growth rate can be made.