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Carbon Cycle & Ecosystems

Measurements from the Gravity Recovery and Climate Experiment (GRACE) satellite mission have thus far been used only to assess mass changes with respect to glaciology and hydrology. The proposed work will attempt to make novel use of GRACE data to assess carbon (CO2) fluxes between the land and the atmosphere, which represent the least understood component of the global carbon cycle. The basis for our work is the realization that because deforestation and other major terrestrial carbon fluxes result in a substantial change in a landscape's biomass over time, they should also lead to minute but detectable changes in the surface gravity field over time. This should particularly be the case in regions with high rates of recent deforestation or high rates of forest regrowth. Although such mass changes would be relatively small compared with other surface mass changes (e.g. on the great ice sheets), there are several reasons why their signals should be detectable by GRACE. Initially this work will focus on land use change (deforestation) in the Amazon, particularly in Brazil, because it has experienced the highest levels of deforestation of any Amazonian country. We will then expand our analysis of the Amazon forest to include undisturbed areas that are thought to be substantial carbon sinks. Once we have completed the analysis of the Amazon carbon budget, we will turn our attention to other tropical regions that have experienced high levels of recent deforestation (Indonesia), as well as extratropical regions widely regarded to be substantial carbon sinks (temperate forests in the U.S.). The exceptionally large spatial rates of deforestation in Brazil and Indonesia -- on the order of 20,000 sq km/yr from 2000-2005, according to the UN FAO and other sources -- would be well-suited to analysis using techniques developed by GRACE experts at NASA-GSFC who are Collaborators on this proposal. In particular, we will adopt the use of high-resolution mass concentration blocks ('mascons'). Over a sufficient interannual period of GRACE measurements (e.g. 2003 to 2009 and beyond), Amazonian and Indonesian deforestation and the resultant biomass losses should lead to secular (non-cyclical) trends appearing in the GRACE data, after we have appropriately accounted for the various other relevant factors (of which seasonal hydrology would be the most important). Likewise, the uptake of carbon in putative sink regions such as U.S. forests should also lead to detectable secular trends in time-varying mass change signals. This study could be a timely and valuable contribution to the scientific understanding of carbon fluxes due to land use change and forest regrowth, which remain among the most poorly understood aspects of anthropogenic climate change and Earth science in general. It represents an innovative approach in several senses: no prior study on terrestrial carbon fluxes has attempted to employ satellite gravity field data; and conversely, no prior study using GRACE data has related to the carbon cycle. Thus, the knowledge gained from this work would be directly relevant to several of NASA's Earth Science Research and Analysis Focus Areas -- primarily the Carbon Cycle and Ecosystems area, but also the areas of Atmospheric Composition; Water and Energy Cycle; and indirectly, Climate Variability and Change, given that land use/cover change and its resulting carbon fluxes substantially affect each of these other aspects. In addition to these research goals, the proposed work also involves a significant education/public outreach (E/PO) component related to a carbon cycle science education course for school teachers, as well as outreach plans with the Science Museum of Minnesota.

Project PI: Pushker Kharecha/NASA GISS

NASA Goddard Institute for Space Studies 2880 Broadway New York, NY 10025 USA

Phone: (212) 678-5536

Email: pkharecha@giss.nasa.gov

http://www.giss.nasa.gov/staff/pkharecha.html

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Started: Sep 29, 2010

Last Activity: Jan 05, 2011

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