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.
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Dissecting the process requires lots of data and on that count OCO-2 is expected to shine. Once in orbit 438 miles above Earth, the spacecraft will collect hundreds of thousands of measurements every day. Its path around the planet will take it over the same spot at the same time every 16 days, allowing scientists to ferret out patterns in carbon dioxide levels over weeks, months and years.
The single instrument aboard OCO-2 is designed gather photons of sunlight glinting off a one-square-mile patch of ground. A grating will split the light into 1,000 different colors and the results analyzed for chemical signatures of carbon dioxide in the air.
The sampling size is small enough so that high carbon emitters may be pinpointed from orbit, information that eventually could be used for monitoring and measuring the effectiveness of policies and procedures implemented to mitigate climate change.
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"In principle, we fully expect to be able to see points where there are large emissions, compared to points nearby, but this is really not a mapping mission," OCO-2 project manager Ralph Basilio, also with the Jet Propulsion Laboratory, told reporters during a prelaunch press conference.
"It's really the fate of carbon dioxide once it's in the atmosphere that we're trying put our finger on," Basilio said.
"I think it's quite remarkable over the past decades we've seen that half the carbon dioxide has been removed by natural processes, but we still aren't quite sure which are the key processes involved," he added. "Trying to get to a point of understanding the details of those processes will give us some insight into the future and what's likely to happen over the next decades, even if we continue to consume more and more fossil fuels and emit more and more carbon dioxide into the atmosphere."
OCO-2 is slated to launch aboard a Delta 2 rocket at 5:56 a.m. EDT on July 1 from Vandenberg Air Force Base in California.