Water vapor is known to be Earth's most abundant greenhouse gas, but the extent of its contribution to global warming has been debated. Using recent NASA satellite data, researchers have estimated more precisely than ever the heat-trapping effect of water in the air, validating the role of the gas as a critical component of climate change.
Andrew Dessler and colleagues from Texas A&M University in College Station confirmed that the heat-amplifying effect of water vapor is potent enough to double the climate warming caused by increased levels of carbon dioxide in the atmosphere.
With new observations, the scientists confirmed experimentally what existing climate models had anticipated theoretically. The research team used novel data from the Atmospheric Infrared Sounder (AIRS) on NASA's Aqua satellite to measure precisely the humidity throughout the lowest 10 miles of the atmosphere. That information was combined with global observations of shifts in temperature, allowing researchers to build a comprehensive picture of the interplay between water vapor, carbon dioxide, and other atmosphere-warming gases. The NASA-funded research was published recently in the American Geophysical Union's Geophysical Research Letters.
"Everyone agrees that if you add carbon dioxide to the atmosphere, then warming will result," Dessler said. "So the real question is, how much warming?"
The answer can be found by estimating the magnitude of water vapor feedback. Increasing water vapor leads to warmer temperatures, which causes more water vapor to be absorbed into the air. Warming and water absorption increase in a spiraling cycle.
Water vapor feedback can also amplify the warming effect of other greenhouse gases, such that the warming brought about by increased carbon dioxide allows more water vapor to enter the atmosphere.
"The difference in an atmosphere with a strong water vapor feedback and one with a weak feedback is enormous," Dessler said.
Climate models have estimated the strength of water vapor feedback, but until now the record of water vapor data was not sophisticated enough to provide a comprehensive view of at how water vapor responds to changes in Earth's surface temperature. That's because instruments on the ground and previous space-based could not measure water vapor at all altitudes in Earth's troposphere -- the layer of the atmosphere that extends from Earth's surface to about 10 miles in altitude.
AIRS is the first instrument to distinguish differences in the amount of water vapor at all altitudes within the troposphere. Using data from AIRS, the team observed how atmospheric water vapor reacted to shifts in surface temperatures between 2003 and 2008. By determining how humidity changed with surface temperature, the team could compute the average global strength of the water vapor feedback.
"This new data set shows that as surface temperature increases, so does atmospheric humidity," Dessler said. "Dumping greenhouse gases into the atmosphere makes the atmosphere more humid. And since water vapor is itself a greenhouse gas, the increase in humidity amplifies the warming from carbon dioxide."
Specifically, the team found that if Earth warms 1.8 degrees Fahrenheit, the associated increase in water vapor will trap an extra 2 Watts of energy per square meter (about 11 square feet).
"That number may not sound like much, but add up all of that energy over the entire Earth surface and you find that water vapor is trapping a lot of energy," Dessler said. "We now think the water vapor feedback is extraordinarily strong, capable of doubling the warming due to carbon dioxide alone."
Because the new precise observations agree with existing assessments of water vapor's impact, researchers are more confident than ever in model predictions that Earth's leading greenhouse gas will contribute to a temperature rise of a few degrees by the end of the century.
"This study confirms that what was predicted by the models is really happening in the atmosphere," said Eric Fetzer, an atmospheric scientist who works with AIRS data at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Water vapor is the big player in the atmosphere as far as climate is concerned."
http://www.nasa.gov
Comments
water vapor
March 29, 2009 by Anonymous, 13 weeks 5 days ago
Comment id: 35699
Five points ignored above.
1. Currently, water vapor concentration is observed to be increasing in our atmosphere only below 4 km while decreasing above 4 kw. So in the upper tropophere (8 - 12 km), where the greenhouse effect is supposed to occur, water vapor is declining.
2. The above article ignores cloud formation which results from higher levels of water vapor; upper ice clouds are strong IR absorbers while low weather clouds are weaker IR absorbers but strong solar radiation blockers (negative feedback). The IPCC has suggested, without scientific proof, that warming increases upper clouds at the expense of the lower weather clouds. Dr Roy Spencer has shown, that in the tropics, warm low fronts cause the opposite effect to occur. Nine consecutive events all show that when the air warmed, both cloud types initially increased, but it is the upper clouds that start to decrease half way through the warming. In fact, they decrease to a point below their starting concentration only to return to the initial amount when the heating event had ended. This definitely suggests that mother nature is countering the warming with a negative feedback.
3. If one examines the ice core data, warming precedes CO2 increase and cooling precedes CO2 decline. This cast doubts on the theory of the greenhouse effect. It is a well established scientific fact that colder water traps greater amounts of CO2 than warmer water. If you pour cold soda into a warm glass, you get much fizz. Since this CO2 reservior (our oceans) far exceeds the amount of CO2 in our atmosphere, warming our oceans will produce higher levels CO2 in the air. This is a major portion of the increase in CO2 today.
4. The whole idea of the greenhouse effect was countered 100 years ago by R. W. Wood. He showed that it is convection processes (warm air rising, cool air sinking) that dominates the heat removal budget from the surface of earth; convection is initiated by conduction on land and evaporation from our oceans. In fact, drawing on this experiment, I estimate that blackbody (IR) radiation accounts for less than 5% of the heat removal budget; probably about 2%. If this is so, than a small increase in a trace gas (CO2) will delay slightly only a small amount of the escaping heat. Maybe this is why no one has been able to detect much heating in the upper troposphere in the last 30 years. If the claimed (IPCC) 0.47 degrees gained at the surface is mostly agw, then according to their own model, the hot spot centered over the equator at 10 km height should haved warmed at least 1 degree C. However, less than 0.1 degree warming has occurred as measured by over 100 radiosonde weather balloons supported by 10,000s satelite measurements. This is a gross failure by NASA and IPCC to prove the greenhouse effect. This means that if the upper troposphere fails to warm substantially, then the CO2 greenhouse mechanism is only a very minor contributor to climate warming.
5. The idea that water vapor can amplify, by a factor of 2.5 to 5 times, the 1.5 degree maximum warming produced by CO2 is counter intuitive. If a gentle warming of 1 degree over a period greater than a century would cause an unending chain reaction; more CO2, more warming, more H20, more warming, more H20 and CO2, more warming, etc. If this were possible, why didn't our exit from the last ice age (a rise of 7 to 10 degrees in a few decades) trigger such an event. In addition, it should be noted that most past inter glacial periods where 2 to 3 degrees warmer than today's period.
6. Remember that CO2 is plant food; CO2 + H2O + solar radiation is what is involved in photosynthesis and plant building. Without the current increase in CO2, starvation would be far worse today. There is no ideal earth temperature; warm is better than cold. Mankind might fail to survive the next ice age. Interglacial periods last 10,000 to 20,000 years (most less than 15,000 years), while ice ages last about 100,000 years. Our current interglacial period is now approaching 11,000 years old. That is the danger we face.
p bartner 3/28/09
lato
March 9, 2009 by Anonymous, 16 weeks 4 days ago
Comment id: 35225
nice article Thanks . lato
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water vapour plays major role in climate change
November 19, 2008 by Anonymous, 32 weeks 2 days ago
Comment id: 32945
I agree with anonymous that it is absurd to reason that there is only positive feedbacks associated with anthropogenic CO2 and alleged resulting evaporation.
There is an inconsistency in Kyoto dogma.
In the Kyoto text, it states that water vapor results from a natural process, and besides it is too difficult to model. The bulk of CO2 is also produced from natural processes.
In the US/Boundary Waters Treaty and water apportionment agreement between the three Canadian prairie provinces, evaporation losses from reservoirs are considered anthropogenic and charged as a water use to the upstream jurisdiction. From regional evaporation charts, for the reservoirs in Canada I estimate annual water vapor loading of 2,600 megatonnes which does not include the probably considerable greater loading from evapotranspiration associted with irrigation. The anthropogenic CO2 loading currently attributed to Canada is about 950 megatonnes for a relatively minor greenhouse gas as compared to water vapor.
Don Farley Water Resources Engineer, Gatineau Quebec Canada
don.farley@sympatico.ca
What about clouds?
November 19, 2008 by Anonymous, 32 weeks 3 days ago
Comment id: 32933
"The answer can be found by estimating the magnitude of water vapor feedback. Increasing water vapor leads to warmer temperatures, which causes more water vapor to be absorbed into the air. Warming and water absorption increase in a spiraling cycle."
This seems to imply only a positive feedback system between CO2 and water. Dr Roy Spencer has published a recent study which shows, from satellite readings, that computer models ignore potential increased negative feedbacks from this increased water vapor. What are the increased negative feebacks ... increased cloud concentration which forms from the water vapor. Clouds, at certain heights, act as natural reflectors of heat and act to cool the planet.
Further, using the anthropic principal, it seems almost absurd to reason there are only positive feedbacks and that the earth's climate is inherently unstable. For, in the past, we have had periods of increasing CO2 and also levels of CO2 up to 10x higher than today. If only positive feedbacks existed and CO2 was the main driver of climate why wasn't there some runaway scenario in the past?
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