According to a new study by the U.S. Geological Survey, the western U.S. ecosystems stretching from the temperate rain forests of the Pacific Northwest to the Arizona deserts and the Rocky Mountains annually absorb as much carbon dioxide as do 83 million vehicles. Gasoline consumption contributes nearly 5% of the total greenhouse gas emissions in the United States. The total amount of carbon stored is nearly 100 million tons.
An area exceeding a million square miles was included in the study which focused on the 2001-2005 period. Within this area, forests, which occupy 28% of the area, are the vegetation type most active in withdrawing and storing carbon from the atmosphere, accounting for 70% of the total regional carbon uptake. Most of the region (nearly 60% ) is occupied by grasslands and shrublands which collectively absorbed and stored 23% of the carbon in the region. Agricultural lands occupy 6% of the total land area and stored 4.5% of the total in 2001-2005. The most active ecosystem type in terms of carbon storage is wetlands which, because they comprise under 1% of the area, contribute less to the regional carbon budget than the major land categories.
In an earlier study, the Geological Survey found that currently the Great Plains ecosystems also are a carbon sink, absorbing more C than is released, thereby counterbalancing the production of some of the greenhouse gases emitted in the region from fossil fuel combustion. The amount of carbon stored in the region, which comprises all or parts of 14 states from Montana to Texas and eastern Iowa, is close to the regional emissions of methane and nitrous oxide, which come from natural gas production and vehicle and power plant activity. In this approach, the release of carbon dioxide, the largest greenhouse gas source, is not counterbalanced by the uptake numbers.
Other regional assessments are expected to be completed by the U.S. Geological Survey “around 2013” at which time a report on the national carbon budget will be released.