Deforestation is the removal of a forest or stand of trees where the land is thereafter converted to a nonforest use. About half of the world original forests had disappeared by 2011, the majority during the last 50 years. Since 1990 half of the rain forests have disappeared. Forests are removed and converted into other forms such as when it is used as fuel which will emit carbon dioxide. A new study with NASA participation has sharply reduced previous estimates of how much carbon was emitted into Earth's atmosphere from tropical deforestation in the early 2000s. Research scientist Sassan Saatchi of NASA's Jet Propulsion Laboratory, Pasadena, Calif., participated in the study, published June 21 in the journal Science. They combined satellite data on gross forest loss and forest carbon stocks to track emissions from deforestation in the world's tropical forests. The resulting gross emissions estimate of 0.81 billion metric tons of carbon emitted per year is approximately one third of previously published estimates, and represents just 10 percent of the total global human-produced carbon emissions over the time period analyzed (2000 to 2005).
Deforestation occurs for many reasons: trees or derived charcoal are used as, or sold, for fuel or as timber, while cleared land is used as pasture for livestock, plantations of commodities, and settlements. The removal of trees without sufficient reforestation has resulted in damage to habitat, biodiversity loss and aridity. It has adverse impacts on biosequestration of atmospheric carbon dioxide. Deforestation has also been used in war to deprive an enemy of cover for its forces and also vital resources. A modern example of this was the use of Agent Orange by the United States military in Vietnam during the Vietnam War.
Two countries - Brazil and Indonesia - produced the highest emissions during the study period, accounting for 55 percent of total emissions from tropical deforestation. Nearly 40 percent of all forest loss in the study region was concentrated in the dry tropics, but accounted for only 17 percent of total carbon emissions, reflecting their relatively low carbon stocks in comparison to those found in tropical moist forests.
The Winrock study is the first study of global carbon emissions from tropical deforestation to use satellite data, rather than tabular bookkeeping models, to account for carbon. This approach allows for a much more refined analysis and yields results that will serve as a better benchmark for monitoring global progress on reducing emissions in the future. Individual emissions numbers were calculated for each country, along with a statistical uncertainty range.
"These detailed emissions estimates would not have been possible without the NASA satellites that helped us quantify forest cover change and forest carbon stocks, which are the two critical data sources for this work," said Saatchi one of the authors. Data from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA's Terra satellite; NASA's Ice, Cloud and land Elevation Satellite (ICESat); NASA's Quick Scatterometer (QuikScat) satellite; and the joint NASA/U.S. Geological Survey Landsat program were used to produce the estimate.
The team hopes the policy mechanism of the United Nations Framework Convention on Climate Change that proposes to compensate developing countries for reducing emissions from deforestation and forest degradation (REDD) will benefit from a more accurate benchmark of emissions from deforestation.
"The relative contribution of deforestation to total greenhouse gas emissions will likely continue to decline through time as emissions from other sectors rise, but the loss of millions of hectares of forest per year remains considerable," said Alexander Lotsch of the World Bank, which funded the study. "Effectively reducing forest-related emissions through international efforts that also promote biodiversity conservation, forest livelihoods and help maintain essential forest functions such as water regulation, is an essential measure to avoid serious climate change impacts and to ensure low carbon sustainable development in the developing world."
Deforestation may cause carbon stores held in soil to be released. Forests are stores of carbon and can be either sinks or sources depending upon environmental circumstances. Mature forests alternate between being net sinks and net sources of carbon dioxide. In deforested areas, the land heats up faster and reaches a higher temperature, leading to localized upward motions that enhance the formation of clouds and ultimately produce more rainfall. Deforestation leads to local and global climate changes in temperature and precipitation.
For further information see Deforestation.
Map image by NASA.