Nature Climate Change | Climate Feedback

AGU 2009: Putting on AIRS at AGU

Harvey Leifert

On Tuesday, AGU attendees heard about an instrument aboard a NASA satellite that has opened a new window into climate change observations, well beyond its original purpose. In NASA’s inspired acronymal lexicon, the instrument is called AIRS, for Atmospheric Infrared Sounder, and it orbits the Earth aboard the Aqua satellite. AIRS was designed to improve weather forecasting, and it has done that, scientists say, but it has also done much more, monitoring greenhouse gases that cause global warming.

In a well-attended press conference prior to their formal session, researchers told reporters that AIRS, containing no moving parts, has proved remarkably robust, measuring carbon dioxide, ozone, water vapor, and carbon monoxide in the mid-troposphere, five to 12 km above Earth’s surface, with far greater precision than anticipated prior to launch in 2002.

In particular, said Moustafa Chahine of NASA’s Jet Propulsion Laboratory, “AIRS provides the highest accuracy and yield of any global carbon dioxide data set available to the scientific community.” Seven years of these data were made available to researchers worldwide in conjunction with the AGU meeting. NASA said it was the first ever release of daily CO2 data based solely on observations.

AIRS researchers have learned over the past seven years that CO2 does not mix well in the troposphere, but is what Chahine called “lumpy,” concentrated more in some places than in others, driven by the jet stream. AIRS has tracked the dispersion of CO2 from Indonesian forest fires, which accounts for a staggering 20% of global anthropogenic CO2. Where does it go? Along with the northern hemisphere’s other CO2 emissions, much of it winds up over the southern hemisphere, according to AIRS measurements, as reported here.


AIRS tracks carbon monoxide, also. The Station fire, which devastated over 40,000 hectares of forest and destroyed scores of homes north of Los Angeles a few months ago, produced strong concentrations of CO over the south central US and over the Great Lakes. Globally, though, CO was most concentrated over central Africa and the Indian Ocean, reported JPL’s Tom Pagano.

Another member of the AIRS team, Andrew Dessler of Texas A&M University, reported on the unique view the instrument is providing of water vapor distribution in the atmosphere, and in particular the feedback of water vapor that he says amplifies warming due to CO2. He warned that warming of a few degrees Celsius is “essentially guaranteed” over the next century, unless there exists a “presently unknown offsetting feedback (e.g., clouds).”

Dessler took issue with a statement, attributed to Lowell Wood, in the recently published book, Superfreakonomics, that current climate models “do not know how to handle water vapor and various types of clouds….I hope we’ll have good numbers on water vapor by 2020 or thereabouts.” Dessler told reporters that AIRS, using the infrared spectrum, sees right through clouds and is providing accurate water vapor data today. Current models do a good job of simulating the water vapor feedback effect, he said.

As with so many sessions here, it was encouraging to know that AIRS scientists are getting so much good data, but somewhat depressing to learn the messages sent down from their instrument.

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    Edward Greisch said:

    Can AIRS data tell me which cities allow leaf burning and which don’t? Does anybody monitor leaf smoke? Leaf smoke is a really bad allergen and I would appreciate the information.