Texas A&M researcher plays key role in NASA's greenhouse gas project

December 15th, 2009

Researchers studying climate now have a new tool at their disposal: daily global measurements of carbon dioxide and water vapor in a key part of Earth's atmosphere. The data are courtesy of the Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua spacecraft and confirm the mainstream scientific view that large changes in the climate are likely over the next century.

Moustafa Chahine, the instrument's science team leader at NASA's Jet Propulsion Laboratory in Pasadena, unveiled the new measurements at a briefing on recent breakthroughs in greenhouse gas, weather and climate research from AIRS at this week's American Geophysical Union meeting in San Francisco. The new data have been extensively validated against both aircraft and ground-based observations. They give users daily and monthly measurements of the concentration and distribution of carbon dioxide in the mid-troposphere - the region of the atmosphere located between 5 and 12 kilometers, or 3 to 7 miles, above Earth's surface and track its global transport.

Users can also access historical AIRS carbon dioxide data spanning the mission's entire seven-plus years in orbit. The product represents the first-ever release of global daily carbon dioxide data that are based solely on observations.

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

"The argument that the scientific community does not understand water vapor is one of the most durable urban legends in the climate change debate," says Andrew Dessler, a climate scientist at Texas A&M University.

"AIRS temperature and water vapor observations have corroborated climate model predictions that the warming of our climate produced by carbon dioxide will be greatly exacerbated - in fact, more than doubled - by water vapor."

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

"The implication of these studies is that, should greenhouse 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 system," Dessler said.

Originally designed to observe atmospheric temperature and water vapor, AIRS data are already responsible for a greater 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 in the frequency and strength of severe storms. Earlier this year, a team of NASA researchers showed how AIRS can significantly improve tropical cyclone forecasting. The researchers studied deadly Typhoon Nargis in Burma 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 the forecasts.

AIRS observes and records the global daily distribution of temperature, water vapor, clouds and several atmospheric gases including ozone, methane and carbon monoxide. With the addition of the mid-tropospheric carbon dioxide data set this week, a seven-year digital record is now complete for use by the scientific community and the public.