http://www.chron.com/disp/story.mpl/nation/6841153.html
2 climate studies offer hope on global warming
Research of carbon dioxide and water vapor levels leads to new insights
By ERIC BERGER
HOUSTON CHRONICLE
Jan. 28, 2010, 10:41PM
A pair of climate papers published this week in the world's top science journals may offer some hope that rising levels of carbon dioxide won't imminently bring the planet to boil.
One paper concerns the effect of a warming climate on oceans and other sources of carbon dioxide on Earth, and found they will be slower to release more CO2, and thus do less to amplify warming than previously expected.
The second study analyzed a decline in water vapor — a potent greenhouse gas — in the upper levels of the atmosphere and found that it may have contributed to a decade-long halt in the rise of global temperatures since 1998.
Both studies are a bit technical, but they are important because they get to the cutting edge of climate science.
Amid the over-reaching catastrophic claims of environmentalists on one side, and cries of global warming being a great hoax from the other, there is actually a good deal of common ground among scientists.
All agree concentrations of CO2 in the atmosphere are increasing, and there's a general agreement that a doubling of CO2 levels this century, by themselves, will produce an increase of 1.5 to 2 degrees Fahrenheit in global temperatures.
Positive feedback
By itself, this would not be catastrophic for the planet.
What scientists are actually interested in better understanding are so-called “feedback” loops from rising CO2 levels, which in turn could substantially amplify warming to catastrophic levels.
For example, as CO2 levels rise, and temperatures go up, the thinking is that the area of the planet covered by snow will decrease. Snow is very effective at reflecting heat back into space, so anything that replaces it will absorb more heat and further warm the planet.
This is a positive feedback. The question is: Will rising CO2 levels produce more positive or negative feedbacks?
For some scientists, including the skeptical Richard Lindzen of the Massachusetts Institute of Technology, the jury on feedbacks remains out.
“Climate science is a field that is not highly developed,” he said. “Really, it's still in its infancy.”
Other climate scientists would disagree, but as the two new papers this week show, researchers are still grappling to understand the balance of feedback loops.
The first study, published Thursday in Nature, concerns the notion that warming from CO2 emitted by human activity will change the “carbon cycle,” thus increasing the rate at which natural reservoirs of CO2 such as the oceans release it back into the atmosphere.
Scientists worry this excess CO2 ejected into the atmosphere could be a powerful positive feedback, accounting for a significant chunk of this century's projected warming.
However, the research, analyzing temperature reconstructions and Antarctic ice cores dating as far back as the year 1050, found that previous estimates of this carbon cycle feedback loop overstated the potential warming.
“If we use these past feedbacks to get a handle on how much amplification of warming is taking place, our results suggest 80 percent less amplification compared to the earlier, higher estimate,” said the study's lead author, David Frank of the of the Swiss Federal Research Institute WSL.
In its most recent report, from 2007, the Intergovernmental Panel on Climate Change used more than a dozen models to project a warming of 3 to 11 degrees Fahrenheit by the year 2100.
However, the primary models used to establish that range of temperatures did not yet include a carbon cycle feedback, said Gavin Schmidt, a NASA scientist who develops computer climate models.
“So any positive feedback makes the situation a little worse from what was presented in IPCC,” he said. “It is of course good news that this is at the low end of previous estimates, but it doesn't alter the big picture.”
Levels declined
The second study released this week concerns another feedback loop, that from water vapor, a far more potent greenhouse gas than CO2 at trapping heat in the atmosphere.
Scientists believe a warmer world will yield higher humidity, raising water vapor levels.
But a new study in the journal Science, published today, found that levels of water vapor in the stratosphere actually dropped between 2000 and 2009. This may explain why the planet has not warmed in the last decade.
The significance of the study is that, until now, scientists haven't appreciated the climatic significance of water vapor in a few-miles- thick band in the stratosphere about 10 miles up.
“Water vapor in this narrow region really packs a wallop, and has a much bigger impact on climate than if you were to increase water vapor levels at a level higher up,” said the study's lead author, Susan Solomon, a National Oceanic and Atmospheric Administration scientist.
During the 1980s and 1990s, levels of water vapor in the stratosphere rose quite dramatically, but in 2000 they suddenly dropped.
“Neither the increase before 2000 nor the decrease in 2000 are well understood,” said Andrew Dessler, an atmospheric scientist at Texas A&M University.
The computer models used to project future temperatures also don't include this feature because it remains poorly understood.
