Water Helps

A recent scientific paper says that besides being a greenhouse gas (the most potent and prevalent) variations in water vapor in the upper atmosphere may help cool the planet.

Why the Earth's surface temperature hasn't warmed as expected over the past decade continues to be a puzzle for scientists. One study out earlier this month theorized that the Earth's climate may be less sensitive to greenhouse gases than currently assumed.

Another surprising factor could be the amount of water vapor way up in the stratosphere, according to a new study out Thursday in the journal Science.

Water vapor, a potent, natural greenhouse gas that absorbs sunlight and re-emits heat, is "a wild card" of global warming, says the paper's lead author, senior scientist Susan Solomon of the National Oceanic and Atmospheric Administration in Boulder, Colo. Solomon was also a co-chair of one of the groups within the Intergovernmental Panel on Climate Change that put out the definitive forecast of global warming in 2007.

In the Science paper, Solomon and her colleagues found that a drop in the concentration of water vapor in the stratosphere "very likely made substantial contributions to the flattening of the global warming trend since about 2000."

While climate warming is continuing — the decade of 2000 to 2009 was the hottest on record worldwide — the increase in temperatures was not as rapid as in the 1990s.

The stratosphere is the layer of the atmosphere just above the troposphere, which is the layer of air here at the planet's surface. (The troposphere goes from the surface up to about 8 miles, and the stratosphere is from about 8 to 30 miles above the surface.)

The decline in water vapor in the stratosphere slowed the rate of surface warming by about 25%, compared to that which would have occurred due to carbon dioxide and other greenhouse gases, notes the study. Specifically, the planet should have warmed 0.25 degree F during the 2000s, but because of the influence of the water vapor, it rose just 0.18 degree F.

"We call this the 10/10/10 paper," says Solomon. "10 miles above your head, there is 10% less water vapor than there was 10 years ago."

Why did the water vapor decrease? "We really don't know," says Solomon, "We don't have enough information yet."

The findings are "surprising," says Bill Randel, an atmospheric chemist at the National Center for Atmospheric Research, who was not part of the study. He said it was surprising how big an effect such a very little change in stratospheric water vapor has had on the surface climate.

If it is part of a feedback mechanism it would mean that the water vapor feedback is less than expected.

If it is related to Galactic Cosmic Rays and the solar magnetic field it would mean that the solar influence on climate is greater than estimated. Either way it reduces the influence of CO2 on the global climate. Which means it is not as bad as we thought.

Osama had better rethink his position on global warming before he becomes a laughingstock.