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NASA Models Show Trees Can Slow Increase of Atmospheric Carbon
Converting marginal agricultural land to forests may help slow the increase of carbon in the atmosphere, according to model-based results obtained by NASA scientists using space-based Earth observations and a state-of-the-art ecosystem model.

cropland Researchers found that on a national basis, converting marginal agricultural lands into forests has the potential to remove hundreds of millions of tons of carbon dioxide from the atmosphere every year. This conversion, known as afforestation, could be used to partially off-set carbon emissions produced by burning fossil fuels.

Left: croplands

“In this study, we primarily wanted to know how much atmospheric carbon dioxide can be absorbed by plant growth over the next 20 to 30 years, if 25 percent or less of the Unites States croplands and rangelands was planted with native tree species,” said Christopher Potter, lead author of the paper in Climatic Change, published by Springer Science+Business Media, and a scientist from NASA Ames Research Center, in California's Silicon Valley. “Our findings showed that at least one-fifth of annual fossil fuel emission of carbon in the United States can be offset by planting new forests,” added Potter.

Using plants and soil to store atmospheric carbon dioxide could become part of our country’s enhanced land use management. Generalized global estimates of stored carbon in afforested areas vary between temperate and tropical regions, but range as high as 4.5 billion tons of carbon per year, say scientists. These estimates are from model results, not actual measurements, and many questions, scientific and economic, must be answered before such land use practices are adopted.

Researchers collected ‘greenness’ data from the Advanced Very High Resolution Radiometer (AVHRR) sensor on the NOAA Polar Operational Environmental Satellite (POES) and entered it into the NASA-Carnegie, Ames, Stanford Approach (CASA) carbon model at 8-kilometers’ spatial resolution. The model generated three different national maps that showed estimates of the amount of carbon absorbed by plants growing in current forests, croplands and rangelands.

When the research was analyzed, the top five states identified as having a high carbon storage potential by converting croplands to newly developed forests were Texas, Minnesota, Iowa, Illinois and Missouri. The top five states with potential for converting rangelands or pastures were Texas, California, Montana, New Mexico and Colorado.

Research suggested that the southeast region of the United States has the most favorable conditions for afforestation due to its subtropical climate. In addition, model results suggested that large areas of croplands in South Dakota, Minnesota and Wisconsin showed potential for carbon management and shouldn’t be underestimated.

Past studies show that managed land use practices can be very productive in removing carbon from the air, but variability in forest growth conditions across diverse climate, soil, water and elevation zones make it difficult to predict outcomes. “If rainfall patterns change, for whatever reason, the risk of losing plants can go up in drought-stricken areas,” noted Potter.

This work was made possible through funding by NASA as part of the long-term USDA Northern Global Change Research Program, which is dedicated to understanding how human-induced and natural changes affect our global environment.

These and related studies appeared in the Springer Science+Business Media issues of Climatic Change, 2007.

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Ruth Marlaire
NASA Ames Research Center