Forests stored 247 billion tons of carbon in the early 2000s: NASA map

Using satellite data, NASA researchers have created the most precise map ever produced depicting the amount and location of carbon stored in Earth's tropical forests.

The map shows for the first time the distribution of carbon stored in forests across more than 75 tropical countries. Most of that carbon is stored in the extensive forests of Latin America.

They found that the tropical forests stored 247 billion tons of carbon in the early 2000s.

The data are expected to provide a baseline for ongoing carbon monitoring and research and serve as a useful resource for managing the greenhouse gas carbon dioxide.

"This is a benchmark map that can be used as a basis for comparison in the future when the forest cover and its carbon stock change," said Sassan Saatchi of NASA's Jet Propulsion Laboratory in Pasadena, California, who led the research.

"The map shows not only the amount of carbon stored in the forest, but also the accuracy of the estimate," Saatchi added.

To arrive at a carbon map that spans three continents, the team used data from the Geoscience Laser Altimeter System lidar on NASA's ICESat satellite. They looked at information on the height of treetops from more than 3 million measurements. With the help of corresponding ground data, they calculated the amount of above-ground biomass and thus the amount of carbon it contained.

The team then extrapolated these data over the varying landscape to produce a seamless map, using NASA imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA's Terra spacecraft, the QuikScat scatterometer satellite and the Shuttle Radar Topography Mission.

They found that forests in Latin America hold 49 percent of the carbon in the world's tropical forests. For example, Brazil's carbon stock alone, at 61 billion tons, almost equals all of the carbon stock in sub-Saharan Africa, at 62 billion tons.

"These patterns of carbon storage, which we really didn't know before, depend on climate, soil, topography and the history of human or natural disturbance of the forests," said Saatchi.

"Areas often impacted by disturbance, human or natural, have lower carbon storage."

The map also provides a better indication of the health and longevity of forests and how they contribute to the global carbon cycle and overall functioning of the Earth system.

The next step in Saatchi's research is to compare the carbon map with satellite observations of deforestation to identify source locations of carbon dioxide released to the atmosphere.

The study is published in the Proceedings of the National Academy of Sciences.