Carbon dioxide emissions in most nations are dominated by the use of fossil fuels—coal, oil, and natural gas. In the tropics, however, deforestation is also a major source of CO2 to the atmosphere.
In other areas, primarily Europe and the U.S., forest lands, cleared for agriculture centuries ago, are now being allowed to return to forest. These areas are known as carbon “sinks,” because this forest growth process takes up carbon from the atmosphere – providing temporary storage in wood and soil that can last for centuries.
The latest national climate assessment indicates that the U.S. forest carbon sink offsets about 25% of our emissions from fossil fuels. This is a helpful, but not sufficient, contribution to reducing our overall emissions.
Estimating the carbon sink in forests is not easy. We must assess not just the area of forested land, but the size and age of the forests. Changes in the storage of carbon in agricultural soils are also part of the U.S. carbon sink.
Discounts to the sink occur when harvested products—like firewood, fuel pellets, and pizza boxes—are burned. A recent assessment suggests that 35% of the apparent U.S. sink for carbon in vegetation is lost from off-site emissions from forests and forest products.
While it is nice to give credit to nations that are re-growing their forests, there is much mischief afoot in the carbon accounting of forests. But, that should not delay our enthusiasm for reductions in the major human source of CO2 in our atmosphere—fossil fuel combustion.
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Photo, taken on July 23, 2012, courtesy of Montgomery County Planning Commission via Flickr.
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