As the battle over climate change legislation slowly grinds into gear, it's likely that part of the struggle will be over credits given for various carbon sinks. In some circles, plant materials fall into that category. However, extensive evidence is suggesting that there are large variations in whether, and under what conditions, specific plants may truly be a carbon sink (see TipSheet of Jan. 6, 2010,  for some of this evidence.
Now a study by Univ. of California-Irvine researchers has found that at least some of the existing 30 million-plus acres of lawn that cover about 2% of the land in the continental US  aren't net carbon sinks. However, their study specifically addressed just a small number of test plots in southern California, so further research is needed to determine how broadly the finding applies, especially in areas subject to less heat and sunshine.
In their study, published Jan. 22, 2010, in Geophysical Research Letters, they found that the grass itself acted as a carbon sink, as other studies have shown. But when they accounted for the fuel burned while maintaining the lawn, the emissions from the fertilizer spread to help it grow, and other related practices, they found that four times as much carbon was emitted than was absorbed by the plants. Athletic fields were the worst performers, since their high maintenance contributed to less carbon absorption and more carbon emissions.
If confirmed, and found to apply broadly in the US, this finding could have substantial impact on the climate change discussion, since sizable lawn acreage might need to be withdrawn from consideration as a source of credit for carbon absorption.
- "Carbon Sequestration and Greenhouse Gas Emissions in Urban Turf,"  by Amy Townsend-Small and Claudia I. Czimczik, doi:10.1029/2009GL041675.
- Press Release, Jan. 19, 2010, "Urban 'Green' Spaces May Contribute to Global Warming."  Media contact: Jennifer Fitzenberger,  949-824-3969.