May 13, 2007
One of the cornerstones of the IPCC`s case is that higher temperatures worldwide resulting from greater concentrations of CO2 should lead to an increase in atmospheric water vapor content-which leads to greater warming. I was over at CCNet and came across this:
NEW STUDY: NO EVIDENCE OF GLOBAL INCREASE IN WATER VAPOUR CONTENT
Paul Biggs <.email@example.com">firstname.lastname@example.org>
The new paper by Smith et al, suggests that there has been no global increase in water vapour content, and undermines the IPCC foundation stone of an enhancement of the increased warming effect of CO2 via increased atmospheric water vapour:
GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L06705, doi:10.1029/2005GL025393, 2006
Variations in annual global precipitation (1979-2004), based on the Global Precipitation Climatology Project 2.5° analysis
Thomas M. Smith et al
The Global Precipitation Climatology Project (GPCP) has produced a combined satellite and in situ global precipitation estimate, beginning 1979. The annual average GPCP estimates are here analyzed over 1979-2004 to evaluate the large-scale variability over the period. Data inhomogeneities are evaluated and found to not be responsible for the major variations, including systematic changes over the period. Most variations are associated with El Niño/Southern Oscillation (ENSO) episodes. There are also tropical trend-like changes over the period, correlated with interdecadal warming of the tropical SSTs and uncorrelated with ENSO. Trends have spatial variations with both positive and negative values, with a global-average near zero.
So, atmospheric water vapor levels have remained the same since 1979. If the Earth were warming as the IPCC models predict, we should have more water vapor in the atmosphere. We don`t. What does that tell us, class?
Nothing that the high priests of global warming are going to listen to, Tim.
Posted by: Morris at May 13, 2007 07:52 PM (23xRk)
> So, atmospheric water vapor levels have remained the same since 1979.
No. The author has misunderstood a critical term in the scientific paper--or perhaps he is deliberately creating a strawman to attack. The paper is about precipitation, not water vapor
If water vapor increases along with temperature, precipitation will not increase.
> What does that tell us, class?
Nothing about water vapor feedback and global warming.
There is still some scientific disagreement about the role of water vapor in climate forcing:
Posted by: Dan Luke at May 14, 2007 08:43 AM (B1j7U)
Not having the entire paper to read, it is difficult to determine. Still, the upshot is that there is no measurable effect from increased water vapor in the atmosphere, which suggests that we are NOT witnessing any significant evaporation.
The fact is, nobody understands the influence of water vapor. That is one of the many problems with anthropogenic global warming theorists.
Posted by: Timothy Birdnow at May 14, 2007 05:49 PM (e+f2q)
Oh, and also bear in mind that the Earth is not going to warm all at once-especially if CO2 is the cause of this warming. We should expect increased percipitation in spots. There should DEFINITELY be a discernable change in weather patterns resulting from this.
Posted by: Timothy Birdnow at May 14, 2007 08:25 PM (e+f2q)
>We should expect increased percipitation in spots. There should DEFINITELY be a discernable change in weather patterns resulting from this.
Yes, and the abstract mentions such changes. Note the last sentence:
"There are also tropical trend-like changes over the period, correlated with interdecadal warming of the tropical SSTs and uncorrelated with ENSO. Trends have spatial variations with both positive and negative values, with a global-average near zero." [emphases mine]
There is nothing about this finding that casts doubt on current IPCC AGW hypotheses. Actually, it tends to support another hypothesis: that average global relative humidity remains constant with rises in temperature (until those increases become extreme). If that hypothesis is correct, global precipitation should also remain relatively constant, although local patterns will change.
Humidity and water vapor are more complicated subjects than most people realize, and there are a lot of misconceptions about them. See:
Posted by: Dan Luke at May 15, 2007 09:37 AM (B1j7U)
Thanks, Dan; you make some good point. Also, I found that link about water vapor very interesting.
Roger Pielke disagrees. Here is a discussion thread about the issue of water vapor/global warming:
Evaporation Is Equal To Precipitation On The Global Scale - Implications To the Conclusion On A Claimed Increase of Atmospheric Water Vapor <http://climatesci.colorado.edu/2007/04/05/evaporation-is-equal-to-precipitation-on-the-global-scale-implications-to-the-conclusion-on-a-claimed-increase-of-atmospheric-water-vapor/>
Filed under: Climate Change Metrics <http://climatesci.colorado.edu/category/climate-change-metrics/> - Roger Pielke Sr. @ 7:00 am
In early March, there were exchanges of e-mails with respect to the Climate Science conclusion regarding the 2007 IPCC Statement for Policymakers <http://www.ipcc.ch/SPM2feb07.pdf> claim on page 7 that
"The average atmospheric water vapour content has increased since at least the 1980s over land and ocean as well as in the upper troposphere. The increase is broadly consistent with the extra water vapour that warmer air can hold."
Climate Science wrote on February 15, 2007 in the weblog "Several Science Errors (Or, At Best Cherrypicking) In the 2007 IPCC Statement For Policymakers", <http://climatesci.colorado.edu/2007/02/15/science-errors-or-at-best-cherrypicking-in-the-2007-ipcc-statement-for-policymakers/>
"This conclusion conflicts with the finding in
Smith, T. M., X. Yin, and A. Gruber (2006), Variations in annual global precipitation (1979-2004), based on the Global Precipitation Climatology Project 2.5° analysis, Geophys. Res. Lett., 33, L06705, doi:10.1029/2005GL025393,
where they write for the period 1979-2004 that precipitation tends
"have spatial variations with both positive and negative values, with a global-average near zero."
The global average precipitation has not changed significantly in the period.
If greater amounts of water vapor were present in the atmosphere, the evaporation/transpiration of water vapor into the atmosphere and thus the precipitation would have to increase when averaged globally and over a long enough time period."
This Climate Science weblog and a subsequent one on March 10 entitled "Scitizen Column Published Entitled 'Scientific Errors With the IPCC Statement for Policymakers'" <http://climatesci.colorado.edu/2007/03/10/scitizen-column-published-entitled-scientific-errors-with-the-ipcc-statement-for-policymakers/>
solicted a range of comments including
On March 10, 2007 Issac Held, a very well respected climate scientist, commented,
" Dear Roger,
Water vapor can certainly increase without an increase in precipitation or evaporation - the residence time of the vapor simply increases. This is precisely what happens in all models, as described in Held and Soden, J. Climate, 2006, and as many others have pointed out before us. Water vapor follows Clausius-Clapeyron in the models, while the evaporation (and therefore precipitation) are determined instead by the changes in radiative energy fluxes, which are relatively small."
".......I don't think that I can explain it any clearer here than we tried to do there. But visualize a bucket with a constant input of water - once it fills and spills over the output will equal the input. Now make the bucket bigger, with the same input and therefore the same output. That's all there is to it. I am afraid that I do not understand your arguement at all."
Gavin Schmidt also commented and wrote,
"I would draw readers attention to the fact that all these points were drawn to Roger's attention when he first made these claims.
It is curious therefore that he should choose to repeat them verbatim."
Climate Science responded to their comments on those weblogs, however, to make sure the issue is clear, I requested that my class this semester at the University of Colorado in Boulder examine the issue (and particular thanks to Laure Montandon and Carl Drews for their insightful contributions!).
As the students documented, the average residence time for water in the atmosphere is 8-9 days. The annual evaporation rate is 45 times the amount of water in the atmosphere at any instant. Thus the atmosphere is a relatively small reservoir for water. Even a small percentage increase in the global evaporation evaporation must result in the same percentage increase in percentage of precipitation increase. This will occur even if the content of water in the atmosphere increases due to a longer residence time.
Thus, while Climate Science agrees with Issac and Gavin that the amount of water in the atmosphere can increase even without an increase in evaporation and precipitation, the claim in the 2007 IPCC SPM is that the atmosphere and the Earth's surface (thus including the sea surface temperatures; SSTs) have warmed. Higher SSTs are expected to be associated with greater evaporation (the actual sea surface evaporation depends on the surface turbulent moisture fluxes which includes the surface layer vertical gradient of absolute humidity, as well as the net radiation received at the surface).
A larger global averaged evaporation, therefore, must be associated with a larger global average precipitation. Thus the lack of an observed increase in precipitation is in conflict with the claim in the IPCC SPM that ""The average atmospheric water vapour content has increased since at least the 1980s over land and ocean as well as in the upper troposphere.The increase is broadly consistent with the extra water vapour that warmer air can hold."
For this statement to be correct, not only must the atmosphere hold more water BUT the surface evaporation must also have increased due to the warmer Earth's surface! That the precipitation has not increased indicates that the evaporation has also not increased. This implies that any warming of the surface where most of the evaporation ocurrs; i.e. the tropical oceans) has been small.
Thus if the global average mass of water vapor has actually increased, it is likely for reasons other than surface and thus tropospheric warming (the residence time of water in the atmosphere could increase, for example, due to aerosol effects on cloud processes which extend their lifetimes, or from the creation of large haze clouds). Alternatively, water vapor content may not have increased at all as the data to quantitatively assess this is quite limited.
The error (or at best incomplete presentation) in the 2007 IPCC SPM with respect to the higher humidities in the atmosphere misleads the policymakers with respect to actual observed changes in the hydrologic cycle. Instead of relying mostly on model results, the IPCC should be presenting observed atmospheric data which supports their claim. The detailed chapters in the IPCC Report will be examined to ascertain if there is substantive evidence to bolster their conclusion.
Thanks again! I`ve really enjoyed our conversation!
Posted by: Timothy Birdnow at May 15, 2007 04:38 PM (4iWSl)
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