SAN FRANCISCO -- NASA has released the first-ever set of carbon dioxide data based only on daily observations by a satellite instrument, a new tool that will help researchers study climate change and improve weather predictions.
The data came from the Atmospheric Infrared Sounder (AIRS) that NASA launched aboard its Aqua spacecraft in 2002. Since then, AIRS has amassed information about carbon dioxide, carbon monoxide, water vapor, methane and temperatures in the mid-troposphere (see multimedia presentations). The mid-troposphere is about three to seven miles above the Earth's surface.
For carbon dioxide, AIRS measures and tracks its concentration and movement as it moves across the globe. Observation data is critical for scientists to validate their models or adjust them to better predict the impact of greenhouse gas emissions on the weather and climate.
The data have already refuted a long-held belief that carbon dioxide is evenly distributed and do so fairly quickly in the atmosphere once it rises from the ground, said Moustafa Chahine, the science team leader of the AIRS project at the Jet Propulsion Laboratory, at the annual meeting of the American Geophysical Union (AGU) in San Francisco Tuesday.
"Contrary to the prevailing wisdom, carbon dioxide is not well mixed in the mid-troposphere," Chahine said. "You can see the jet stream splitting the carbon dioxide clump."
AIRS data shows instead that carbon dioxide, which has seen its rate of increase accelerating from 1 part per million in 1955 to 2 parts per million today, would require about two to three years before it blends in, he said. The atmosphere currently has about 400 parts per million.
How well and how quickly carbon dioxide blends in is important for understanding how much and how long carbon dioxide remains in the atmosphere and affects the climate before some of it is scooped up by Earth's natural scrubbers, such as the ocean.
And by extension, that knowledge would be crucial in determining what humans must do to minimize their emissions or use technologies to capture and sequester their carbon dioxide pollution before it escapes into the atmosphere.
Chahine said several climate models have assumed an even distribution because researchers didn't have adequate data to show how the carbon dioxide is vertically transported through the atmosphere.
"The data we have now will help researchers improve their models' vertical transport," Chahine said.
Data from AIRS also has yielded another key finding: the southern Hemisphere is actually home to a large concentration of carbon dioxide, a phenomenon that some researchers had speculated about but never had the data to prove it.
Most of the man-made carbon dioxide tends to come from the northern hemisphere, where key polluters such as the United States, China and India are located. In fact, the north produces about three to four times more carbon dioxide than the south, Chahine said.
Although scientists knew that carbon dioxide doesn't stay in one location – winds blow pollution from Asia across the Pacific to reach the United States – their models largely showed a smaller amount of the emission move from the north to the south than what data from AIRS have demonstrated.
"The southern hemisphere is a net sink. Some people say it's the garbage dump for the northern hemisphere," Chahine said, adding that carbon dioxide has the lifespan of 100 years.
Information gathered by AIRS also has pointed to the important role water vapor plays in global warming.
Water vapor is the evaporation of water from the ocean, thunderstorms or other sources. Its presence is closely tied to the temperature of the Earth's surface. As humans emit more carbon dioxide into the atmosphere, the world gets warmer and more humid. That boosts the amount of water vapor, which, because it's a greenhouse gas itself, would in turn amplify the warming trend.
"AIRS has provided an unprecedented view of water vapor distribution," said Andrew Dessler, a climate scientist at the Texas A&M University, at the AGU meeting. "Warming over the next century is essentially guaranteed to happen few degrees Celsius unless" other, previously undiscovered factors show up.
In fact, water vapor can more than double the warming effect of carbon dioxide, Dessler said. He said the data from AIRS corroborated predictions by climate models on the impact of water vapor on global warming.
AIRS is set to end its mission in 2017, when the fuel for Aqua is expected to run out.Photo of AIRS via NASA.