Study Finds Stratospheric Water Vapor Is An Important Driver of Decadal Global Surface Climate Change
30 January 2010
A 10% drop in stratospheric water vapor concentrations acted to slow the rate of increase in global surface temperature over 2000-2009 by about 25% compared to that which would have occurred due only to CO2 and other greenhouse gases, according to a new study by researchers from NOAA Earth System Research Laboratory; the University of Colorado, Boulder; and the University of Bern (Switzerland). Their paper was published online in the journal Science on 28 January.
Earlier observations from satellites and balloons suggest that stratospheric water vapor probably increased between 1980 and 2000, which would have enhanced the decadal rate of surface warming during the 1990s by about 30% compared to estimates ignoring this change, according to the authors.
These findings show that stratospheric water vapor represents an important driver of decadal global surface climate change.
—Solomon et al.
Over the last century, global average surface temperatures have warmed by about 0.75 °C (0.42 °C), with much of it occuring the last half. However, note the authors, the trend in global surface temperatures has been nearly flat since the late 1990s despite continuing increases in the forcing due to all the greenhouse gases.
Previous studies suggested that stratospheric water vapor might contribute significantly to climate change. The new study is the first to relate water vapor in the stratosphere to the specific variations in warming of the past few decades.
Stratospheric water vapor and radiative processes. Source: NOAA. Click to enlarge. |
The stratosphere is the region of the atmosphere from about eight to 30 miles above the Earth’s surface. Water vapor enters the stratosphere mainly as air rises in the tropics.
Stratospheric water vapor changes affect the fluxes of longwave (infrared) and—to a lesser extent—shortwave (solar) radiation, and can thereby influence the temperature in the stratosphere and troposphere. In general, increases in stratospheric water vapor cool the stratosphere, but warm the troposphere; the reverse is true for decreases in stratospheric water vapor.
The researchers used data from the HALogen Occultation Experiment (HALOE) that flew on the Upper Atmosphere Research Satellite (UARS) from late 1991 through November 2005, with coverage from the troposphere to the stratosphere overs 65°S to 65 °N. Combined with two additional and independent sets of satellite data, the data provide evidence for “a sharp and persistent drop of about 0.4 parts per million by volume (ppmv)” in stratospheric water vapor after 2000.
Balloon data suggest a gradual mid-latitude increase in lower stratospheric water vapor of more than 1 ppmv from about 1980 to 2000. Other data also support increased in lower stratospheric water vapor during the 1990s of about 0.5 ppmv.
...recent observations have suggested a correlation of the post-2000 stratospheric water vapor decrease to sea surface temperature [SST] changes near the tropical warm pool region and associated cooling of the cold point that governs water vapor input to the stratosphere in the tropics. However, the relationship between SSTs in the warm pool region and stratospheric water vapor changes character (from negative to positive short-term correlations) from 1980–2009, suggesting that other processes may also be important, or that the correlation may be a transient feature linked to the specific pattern of SSTs at a given time rather than to the average warming of SSTs around the globe.
It is therefore not clear whether the stratospheric water vapor changes represent a feedback to global average climate change or a source of decadal variability. Current global climate models suggest that the water vapor feedback to global warming due to carbon dioxide increases is weak but these models do not fully resolve the tropopause or the cold point, nor do they completely represent the QBO, deep convective transport and its linkages to SSTs, or the impact of aerosol heating on water input to the stratosphere.
This work highlights the importance of stratospheric water vapor for decadal rates of warming based directly upon observations, illuminating the need for further observations and a closer examination of the representation of stratospheric water vapor changes in climate models aimed at interpreting decadal changes and for future projections.
—Solomon et al.
Authors of the study are Susan Solomon, Karen Rosenlof, Robert Portmann, and John Daniel, all of the NOAA Earth System Research Laboratory (ESRL) in Boulder, Colo.; Sean Davis and Todd Sanford, NOAA/ESRL and the Cooperative Institute for Research in Environmental Sciences, University of Colorado; and Gian-Kasper Plattner, University of Bern, Switzerland.
Resources
Susan Solomon, Karen Rosenlof, Robert Portmann, John Daniel, Sean Davis, Todd Sanford, Gian-Kasper Plattner (2010) Contributions of Stratospheric Water Vapor to Decadal Changes in the Rate of Global Warming. Science Express doi: 10.1126/science.1182488
"A 10% drop in stratospheric water vapor concentrations acted to slow the rate of increase in global surface temperature over 2000-2009 by about 25% compared to that which would have occurred due only to CO2 and other greenhouse gases"
So, this is certain?
Posted by: kelly | 30 January 2010 at 08:26 AM
Kelly: So this is certain.
It seems rather tentative to me after a very quick reading. But others with far more knowledge will be commenting soon.
Posted by: Ken | 30 January 2010 at 10:30 AM
Hate to sound cynical - this looks like a major CO2 backpedal. But in the right direction since we know that 80% of the greenhouse effect results from water vapor. The lead author Soloman is a major AGW proponent.
Posted by: sulleny | 30 January 2010 at 10:58 AM
....It is not clear whether stratospheric water vapor changes represent a feedback to global climate changes OR is a source of decadal variability....
Can anybody answer this question with acceptable support data?
Posted by: HarveyD | 30 January 2010 at 12:19 PM
I read it as global warming would be 25% worse if not for this 10% water vapor drop.
But to know/state whether this drop is normal/abnormal, to continue/increase/decrease needs more $$$/study.
Posted by: kelly | 30 January 2010 at 02:42 PM
Hate to sound cynical
But you do it so well... ;^) This isn't a backpedal, it's just more information. We've always known water vapour is a GHG but its not a forcing agent. H2O, when it is in the troposphere (the lower part of the atmosphere), is a feedback effect. Simply put, any artificial perturbation in water vapour concentrations is too short lived to change the climate. Too much in the air will quickly rain out, not enough and the abundant ocean surface will provide the difference via evaporation. But once the air is warmed by other means, H2O concentrations will rise and stay high, thus providing the feedback. Or at least that's true when the H2O is in the lower part of the atmosphere. This study "Finds Stratospheric (the atmospheric layer above the troposphere) Water Vapor Is An Important Driver of Decadal Global Surface Climate Change." This water vapour is still only a feedback but because it has reached a higher atmospheric level it has a longer residence time because it's on the other side of the tropopause (the boundary between the troposphere and stratosphere).
On average the lowest part of the troposphere is warmest and temperature decreases with altitude. This promotes vertical mixing because warm air rises. In the stratosphere temperature increases with height, which restricts turbulence and mixing. Any water vapour that gets as high as the stratophere will stay there for a longer (decadal) time scales.
http://www.grist.org/article/water-vapor-accounts-for-almost-all-of-the-greenhouse-effect/
Posted by: ai_vin | 30 January 2010 at 03:52 PM
I would imagine, but don't actually know for sure, that the difficulty of water vapour getting into[?] and leaving the stratophere creates a lagging effect where the changes from forcing agents in the lower atmosphere are felt later. I for one would like to know if this guess of mine holds water - pun intended.
Posted by: ai_vin | 30 January 2010 at 04:11 PM
@ai_vin - water vapor seems to stay in the stratosphere on the order of years.
This post on the Wunder Blog says it takes about 1.2 years for water vapor to reach the stratosphere.
http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=1421&theprefset=BLOGCOMMENTS&theprefvalue=0
There's a nice chart which illustrates the seasonality of water vapor concentrations in the stratosphere.
Posted by: Dave R | 30 January 2010 at 08:51 PM
Not quite, what it says is; "Once in the lower stratosphere, the waver vapor takes about 1.2 years to travel to the upper stratosphere" and "its potency is much higher when it is located in the lower stratosphere where temperatures are extremely cold." How much time does it spend in the stratophere as a whole - both the upper and lower parts? Interesting link BTW, thanks.
Approximately 99.13% of the Earth's water vapour is contained in the troposphere (where its residence time is only about 10 days), only a very small amount reaches the stratophere in the first place.
Posted by: ai_vin | 30 January 2010 at 09:41 PM
So water vapor is labeled as the most prevalent GHG, but magically it does not contribute GW because of it's short half-life in the atmosphere? I think this article says different. CO2 is 9% to 30% of GW. What is responsible for the rest?
"We've always known water vapour is a GHG but its not a forcing agent." Sounds like semantic nonsense to me. Is it a GHG that contributes to GW or not?
Think about it. With no CO2 in the air water vapor would still have a significant GW effect. It helps keep the plant warm. Feedback? Sure, but also a direct effect. That's common sense science. It's labeled as "GHG" for a reason.
Posted by: mds | 31 January 2010 at 01:10 AM
water vapor is good to certain extent because it forms cloud which limits the solar radiation. Water on the earth surface vaporize when it absorbs heat thus it indirectly balances the excess heat from sunlight.
To tackle the global warming, we really need to find ways to bring water to desert area. high temperature desert surface is a really bad news.
Posted by: Account Deleted | 31 January 2010 at 04:38 AM
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