CO₂'s Little Helper

A new set of satellite data indicates that further global warming is "essentially guaranteed" due to the amplifying effects of water vapor on warming from the greenhouse gas CO₂, scientists announced yesterday.

Water vapor—which is itself a greenhouse gas—will more than double the climate warming effects from CO₂, unless some as-yet-unknown factor cancels out that effect, climatologist Andrew Dessler of Texas A&M University said at the American Geophysical Union meeting in San Francisco.

Dessler and his colleagues unveiled seven years' worth of global maps of greenhouse gases, including CO₂, methane, and water vapor, acquired by the Atmospheric Infrared Sounder (AIRS) aboard NASA's weather satellite Aqua. The AIRS instrument measured gas levels in the mid-troposphere, which lies 5–12 km above Earth's surface.

Scientists have believed for years that water vapor plays a key role in climate change, but this is the first time observations have corroborated this. The new data validate models that have predicted that when global temperatures rise from increased atmospheric CO₂, the atmosphere becomes more humid, which further increases temperatures.

Clouds with increased moisture, and thus increased reflectivity, could potentially reduce the effect, Dessler said.

The AIRS project was to complement NASA's Orbiting Carbon Observatory, which crashed minutes after launch (C&EN, March 2, page 30). OCO would have orbited three minutes ahead of Aqua and mapped CO₂ sources and sinks from Earth's surface to 20 km high.

The scientists said they hope NASA will eventually launch a new OCO. "We are keeping a spot warm for it in front of Aqua," AIRS team leader Moustafa Chahine said.

CAPTURING CO₂

NASA's AIRS instrument mapped global tropospheric CO₂ levels, shown in this animation. Red indicates higher levels.

WATER WARMING

An animation of AIRS measurements from June to November 2005 shows the global transport and distribution of water vapor.