Forest trees are renowned for their ability to store large amounts of carbon dioxide in their trunk and roots. And for that very reason they've long been regarded as mother nature's anti-dote for our carbon-emitting ways. That is until they're chopped down or burned, causing all that pent up greenhouse gas to be released back into the atmosphere.
It's been estimated that the loss of forests contribute 15 to 20 percent of global carbon emissions, and most of that contribution comes from tropical regions. So to help keep tabs on the rapidly growing deforestation problem, NASA has culled available data from its network of satellites to generate a map that depicts the amount and distribution of carbon stored in Earth's tropical forests.
The accuracy of the map's information will allow nations to better manage greenhouse gases. For instance, governments participating in the Reducing Emissions from Deforestation and Degradation program or REDD+ can use the measurements to establish a monetary value for the carbon sequestered in forests. This means incentives can be offered for countries to preserve their forests and invest in low-carbon development projects.
Prior estimates estimates were derived from a rudimentary process where researchers would manually measure the size of forest trees, a technique that was only reliable enough to produce estimates on local and large scales within a single continent. This is because the structure of forests varies greatly, and the number of ground sites is very limited.
To create the map, the research team used data from the Geoscience Laser Altimeter System lidar on NASA's ICESat satellite. They arrived at their carbon estimates by looking 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 data was then rendered into a visual representation that shows distribution of carbon stored in forests across more than 75 tropical countries. This was achieved 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.
Here are a few striking highlights:
- The most obvious fact you'll notice is that the majority of carbon is stored in the extensive forests of Latin America. The region holds half of all the carbon found within the world's tropical forests.
- Brazil's carbon stock alone, at 61 billion tons, almost equals all of the carbon stock in sub-Saharan Africa, at 62 billion tons.
- The map reveals that in the early 2000s, forests in the 75 tropical countries studied contained 247 billion tons of carbon, which is nearly 25 times the amount of carbon is released annually to the atmosphere from combined fossil fuel burning and land use changes.
"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 Sassan Saatchi of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Areas often impacted by disturbance, human or natural, have lower carbon storage."
For climate change scientists, the map also serves as a barometer 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.
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