One of the more puzzling aspects of climate change is why no matter what amount of carbon ends up in the atmosphere Earth's plants and ocean reabsorb about half.
At least that's been the pattern for more than 50 years, data from ground-based instruments shows.
Scientists are hoping for a new perspective on the long-standing mystery with a NASA satellite that will, for the first time, make carbon dioxide measurements globally from space.
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The Orbiting Carbon Observatory-2, a replacement for a similar spacecraft lost in a 2009 launch accident, will analyze sunlight reflected off Earth for telltale chemical fingerprints of carbon dioxide, a greenhouse gas that plays a major role in the planet's changing temperature.
Every year about 40 billion tons of carbon ends up in Earth's atmosphere, an amount that is increasing as the developing world modernizes, said atmospheric scientist Michael Gunson, with NASA's Jet Propulsion Laboratory in Pasadena, Calif.
"At the same time, we can see that we have this annual cycle of (carbon levels) dropping every summer ... as the forests and plants start to grow. This is the Earth breathing," said Gunson, project scientist for the $465 million mission, known as OCO-2.