# NASA Outlines Recent Breakthroughs in Greenhouse Ga s

Research

Animation of the distribution of mid-tropospheric c arbon dioxide. The transport of carbon dioxide arou nd the world is carried out in the "free atmosphere" above the surface layer. We c an observe the transport of carbon dioxide across t he Pacific to North America, then across the Atlantic to Europe and the Mediterranean to Asia and back around the globe. T he enhanced belt of carbon dioxide in the southern hemisphere is also c learly visible. Image credit: NASA › Play animation (Quicktime) | › Play animation (Windows Media Player) | › Related images and animations

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December 15, 2009

WASHINGTON – Researchers studying carbon dioxide, a leading greenhouse gas and a key driver of global climate change, now have a n ew tool at their disposal: daily global measurements of carbon dioxide in a key part of our atmosphere. The data are courtesy of the Atmospheric Infrared Sounder (AIRS) instrume nt on NASA's Aqua spacecraft.

Moustafa Chahine, the instrument's science team lea der at NASA's Jet Propulsion Laboratory, Pasadena, Calif., unveiled the new prod uct at a briefing on recent breakthroughs in greenhouse gas, weather and climat e research from AIRS at this week's American Geophysical Union meeting in San Fr ancisco. The new data, which span the seven-plus years of the AIRS mission, meas ure the concentration and distribution of carbon dioxide in the mid-troposphe re--the region of Earth's atmosphere that is located between 5 to 12 kilometers, or 3 to 7 miles, above Earth's surface. They also track its global transport. The product repres ents the first-ever release of global carbon dioxide data that are based solely on observ ations. The data have been extensively validated against both aircraft and gro und-based observations.

"AIRS provides the highest accuracy and yield of an y global carbon dioxide data set available to the research community, now and for th e immediate future," said Chahine. "It will help researchers understand how this elusi ve, long-lived greenhouse gas is distributed and transported, and can be used to dev elop better models to identify 'sinks,' regions of the Earth system that store carbon dioxi de. It's important to study carbon dioxide in all levels of the troposphere."

Chahine said previous AIRS research data have led t o some key findings about midtropospheric carbon dioxide. For example, the data have shown that, contrary to prior assumptions, carbon dioxide is not well mixed in th e troposphere, but is rather "lumpy." Until now, models of carbon dioxide transport have assumed its distribution was uniform.

Carbon dioxide is transported in the mid-tropospher e from its sources to its eventual

sinks. More carbon dioxide is emitted in the heavil y populated northern hemisphere than in its less populated southern counterpart. As a re sult, the southern hemisphere is a net recipient, or sink, for carbon dioxide from the nor th. AIRS data have previously shown the complexity of the southern hemisphere's carbon dioxide cycle, revealing a neverbefore-seen belt of carbon dioxide that circles the globe and is not reflected in transport

models.

In another major finding, scientists using AIRS dat a have removed most of the uncertainty about the role of water vapor in atmosp heric models. The data are the strongest observational evidence to date for how wa ter vapor responds to a warming

climate. 

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- 196"AIRS temperature and water vapor observations have corroborated climate model predictions that the warming of our climate produce d as carbon dioxide levels rise will be greatly exacerbated -- in fact, more than doubled - - by water vapor," said Andrew Dessler, a climate scientist at Texas A&M Universit y, College Station, Texas.

Dessler explained that most of the warming caused b y carbon dioxide does not come directly from carbon dioxide, but from effects know n as feedbacks. Water vapor is a particularly important feedback. As the climate war ms, the atmosphere becomes more humid. Since water is a greenhouse gas, it serves a s a powerful positive feedback to the climate system, amplifying the initial warming. AIR S measurements of water vapor reveal that water greatly amplifies warming caused by increased levels of carbon dioxide. Comparisons of AIRS data with models and r e-analyses are in excellent agreement.

"The implication of these studies is that, should g reenhouse gas emissions continue on their current course of increase, we are virtually certain to see Earth's climate warm by several degrees Celsius in the next century, unless some strong negative feedback mechanism emerges elsewhere in Earth's climate syst em," Dessler said.

Originally designed to observe atmospheric temperat ure and water vapor, AIRS data are already responsible for the greatest improvement to five to six-day weather forecasts than any other single instrument, said Chahine. JPL scientists have shown a major consequence of global warming will be an increase i n the frequency and strength of severe storms. Earlier this year, a team of NASA re searchers showed how AIRS can significantly improve tropical cyclone forecasting. The researchers studied deadly Typhoon Nargis in Burma (Myanmar) in May 2008. They found the uncertainty in the cyclone's landfall position could have been reduced by a factor of six had more sophisticated AIRS temperature data been used in th e forecasts.

AIRS observes and records the global daily distribu tion of temperature, water vapor, clouds and several atmospheric gases including ozon e, methane and carbon monoxide. With the addition of the mid-tropospheric carbon di oxide data set this week, a sevenyear digital record is now complete for use by the scientific community and the public.

For more on AIRS, see http://airs.jpl.nasa.gov/

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Alan Buis 818-354-0474 Jet Propulsion Laboratory, Pasadena, Calif. Alan.buis@jpl.nasa.gov

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