The mission's purpose is to map global CO2 concentration in the atmosphere, which scientists can use to pinpoint sources of CO2 emissions and areas where CO2 is being removed from the air through absorption, called "sinks." Currently, researchers make only about one hundred measurements per week of atmospheric CO2 from sites around the globe, primarily by hand-filling empty vials with air and shipping them back to laboratories to be tested. In contrast, the Orbiting Carbon Observatory will collect almost 4 million weekly measurements.
"That's a tremendous amount of measurements compared to what we have right now," said project principal investigator Dr. David Crisp, of NASA's jet propulsion laboratory.
"While our current measurements are very precise, there just aren't enough sites to give us a full picture of where carbon is being emitted and absorbed, and there are places where it's very difficult to make CO2 measurements from the ground. The only right way to do that is to go to space and do it from a satellite orbiting earth," Crisp said.
The satellite will measure CO2 concentrations by gauging the amount of reflected sunlight from the earth's atmosphere that travels back into space. Gases like CO2 absorb only certain colors of light, and most of those colors are in the infrared spectrum, beyond what the human eye can see. Using an instrument called a spectrometer, the satellite will measure how much of the sun's light is absorbed by CO2, allowing scientists to calculate the actual number of CO2 molecules in very precise atmospheric slices.
Anna Michalak, a climate scientist at the University of Michigan, will lead a team of "carbon cartographers" to make the first CO2 concentration maps from the satellite's data.
Michalak explained that even though the measurements will be more precise and numerous than any previous data, there are still areas of the atmosphere the satellite won't be able to cover.
"If you think of the earth as a basketball, and of someone wrapping dental floss around it, you will have a lot of strips of dental floss, but you won't be able to get the whole thing covered by any means," Michalak said. That's why Michalak's team and other scientists will use the data in sophisticated computer models, which are similar to those used in weather prediction, to gain a fuller picture of how the carbon cycle works.
Many scientists are particularly curious about what the new data may reveal about an intriguing--and baffling--phenomenon called "the mystery of the missing sinks."
In the earth's natural carbon cycle, trees, land plants and oceans can act as carbon sinks. Scientists know that humans emit approximately 8 billion tons of carbon into the atmosphere every year, mostly through burning fossil fuels. But of those 8 billion tons of carbon, less than 4 billion tons remain in the atmosphere. Scientists know that the oceans absorb about 2 billion tons but that leaves more than 2 billion tons of carbon being absorbed somewhere on land. And scientists working on land haven't been able to find evidence that trees and plants absorb that much CO2.
"Something is doing us this huge favor, absorbing this large amount of CO2 every year very effectively somewhere on earth, but we don't know what or where it is," Crisp said. "That's what we mean when we talk about the missing sink."
According to Crisp, there's another intriguing layer to the mystery of the missing sink. "The bigger puzzle is that the amount of CO2 that stays in the atmosphere from one year to the next changes dramatically," he said. "Some years the earth absorbs almost all of the CO2 that humans emit, and other years it absorbs almost none. We don't know why."
The forces behind these large swings in CO2 absorption from year to year are crucial for scientists to understand, Crisp said, in order for them to predict with any accuracy how fast CO2 will build up in the long term and thus, how much time we have to adapt climate change.
The Orbiting Carbon Observatory will join a series of five satellites called the A-Train that are already making measurements of plant life in the ocean, cloud distribution, smog levels and other gases. The NASA team has also been working closely for the past four years with the Japan Aerospace Exploration Agency, which launched its Ibuki (Breath) satellite in January.
While NASA's satellite will measure CO2 sinks, Ibuki will concentrate on CO2 sources. Crisp says the teams are looking forward to sharing data and results, both with each other and the global scientific community.
"We can't do it all by ourselves," Crisp said. "For earth science, it's especially important for us to collaborate."
Editor's note: This story was updated on Feb. 23.