Analysis of seven years of data from the Atmospheric Infrared Sounder (AIRS) instrument on NASA’s Aqua satellite indicates that increased levels of atmospheric water vapor, a naturally occurring greenhouse gas, creates a powerful positive feedback loop which could more than double the climate warming effects from carbon dioxide, absent any yet-unidentified factor that could mitigate the effect.
|NASA’s Atmospheric Infrared Sounder (AIRS) instrument prior to installation in the Aqua satellite, launched in 2002. Source: NASA. Click to enlarge.|
The findings were presented by climatologist Andrew Dessler of Texas A & M University at last week’s American Geophysical Union conference in San Francisco. Although scientists have long believed that water vapor is a key amplifier of the effects of climate change, efforts to quantify the potential effect have so far been elusive. However, the AIRS instrument now provides observational data that has been used to validate earlier computer models. The models had predicted a rise in humidity resulting from increased atmospheric levels of carbon dioxide, producing water vapor which in turn would store more heat.
The AIRS instrument measures gas levels in the mid-troposphere, which lies approximately 5 to 12 kilometers (3 to 7 miles) above Earth’s surface, and is an important transport layer for greenhouse gases, including CO2, methane, and water vapor. Clouds that hold increased moisture, and thus increased reflectivity, could potentially reduce the effect.
“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.
The AIRS project was originally designed to complement NASA’s Orbiting Carbon Observatory (OCO) (earlier post) as part of an international “A-Train” of climate satellites. However, OCO crashed in February after failing to reach orbit (earlier post). OCO would have orbited three minutes ahead of Aqua, mapping CO2 sources and sinks from Earth’s surface to as high as 20 kilometers (12 miles).
Last week, the US Senate approved funds to construct and launch a second Orbiting Carbon Observatory. The measure had already been approved by the House of Representatives, and is expected to be signed by President Obama.