From AGU highlights, measurements from 2002 to 2009 show short term feedback still subject to short-term climate variability, long term feedback still in the realm of models.
Measuring the effect of water vapor on climate warming
Water vapor is a potent greenhouse gas. In the atmosphere, the concentration of water vapor increases with the temperature, setting up a powerful positive feedback loop. This water vapor feedback is the strongest known positive feedback, with the potential to roughly double the effect of warming caused by other sources. Determining the exact strength of the water vapor feedback, then, is incredibly important to limiting uncertainty in future climate change projections.
From 2002 to 2009, an infrared sounder aboard NASA’s Aqua satellite measured the atmospheric concentration of water vapor. Combined with a radiative transfer model, Gordon et al. used these observations to determine the strength of the water vapor feedback. According to their calculations, atmospheric water vapor amplifies warming by 2.2 plus or minus 0.4 watts per square meter per degree Celsius. This value, however, is only the “short-term” feedback—the strength of the feedback as measured during the observational period. This value is subject to short-term climate variability. The true value of the feedback, the “long-term” value, is what the short-term observed values should trend towards when given enough time.
Using a series of climate models, the authors estimate the strength of the long-term water vapor feedback. Extrapolating from their short-term observations they calculate a long-term feedback strength of 1.9 to 2.8 watts per square meter per degree Celsius. They find that most models get to within 15 percent of their long-term value within 25 years. The accuracy of calculations, then, could be improved with a longer set of observations.
Source: Journal of Geophysical Research-Atmospheres, doi: 10.1002/2013JD020184, 2013 http://onlinelibrary.wiley.com/doi/10.1002/2013JD020184/abstract
Title: An observationally based constraint on the water-vapor feedback
Authors: N. D. Gordon: Lawrence Livermore National Laboratory, Livermore, California, USA; A. K. Jonko: National Center for Atmospheric Research, Boulder, Colorado, USA; P. M. Forster: School of Earth and Environment, University of Leeds, Leeds, UK: K. M. Shell: College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, Oregon, USA.
Abstract:
The increase in atmospheric concentrations of water vapor with global warming is a large positive feedback in the climate system. Thus, even relatively small errors in its magnitude can lead to large uncertainties in predicting climate response to anthropogenic forcing. This study incorporates observed variability of water vapor over 2002–2009 from the Atmospheric Infrared Sounder instrument into a radiative transfer scheme to provide constraints on this feedback. We derive a short-term water vapor feedback of 2.2 ± 0.4 Wm−2K−1. Based on the relationship between feedback derived over short and long timescales in twentieth century simulations of 14 climate models, we estimate a range of likely values for the long-term twentieth century water vapor feedback of 1.9 to 2.8 Wm−2K−1. We use the twentieth century simulations to determine the record length necessary for the short-term feedback to approach the long-term value. In most of the climate models we analyze, the short-term feedback converges to within 15% of its long-term value after 25 years, implying that a longer observational record is necessary to accurately estimate the water vapor feedback.
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Seeing that atmospheric CO2 was over 1000 and as much as 8000 ppm in dinosaur days without the planet going Venus, I would say that there is no strong positive feedback loop.
The notion of strong positive water vapor feedback is not supported by observations. We have slightly more than 13 years of CERES radiative balance measurements right now, which have their own problems, but still, they indicate a pretty attenuated response to increasing carbon dioxide mixing ratio.
Isolate the water vapor variable from all other possible feed backs in the real world, clouds, precipitation, aerosols,, then plug it into faulty models and create the scenario that fits the established projections —- catastrophe.
Full paper at:
http://www.researchgate.net/publication/259534208_An_observationally_based_constraint_on_the_water-vapor_feedback/file/9c96052cf1064dc1af.pdf
This paper derives water vapor feedback from 2002 to 2009 to be 2.2 W/m2/1.0C. This amount is roughly equivalent to an increase in water vapor of 7.0% per 1.0C increase in temperatures which is also the number that is derived from the Clausius Clapeyron relation and is central to the global warming theory.
The recent IPCC AR5 report revised their water vapor feedback assumption down to 2.0 W/m2/K from 2.3 W/m2/K in previous reports. This AR5 feedback value results in a CO2 sensitivity of 2.52C per doubling (including the values for the other feedbacks like cloud and albedo) but for some reason, this sensitivity number was not outlined in the report.
But here is a far longer timeseries of water vapor feedback going from 1948 to Feb 2014. Its from NCEP Reanalysis (starting in 1948) and from RSS (starting in 1988) which uses SSM/I F08 through F15, SSMIS F16 and F17, AMSR-E, WindSat and cross-calibrates with ground-based GPS water vapor data demonstrate. This then includes far more data than this study which just uses the AIRs satellite data.
So this chart shows water vapor back to 1948 and the forecasts from IPCC AR5 (which is lower than this study) and also the ENSO since it seems to be the main governing factor.
http://s27.postimg.org/eexakr5wz/ENSO_PCWV_48_Feb14.png
Yeah, the models are way off.
In addition, if one starts the data at 2002 and then ends in 2009, right at the height of a very large El Nino, you are going to get a large positive feedback value. But this cherrypicking.
Starting in 1958 versus the lower troposphere temps, the water vapor feedback is only 4.14% per 1.0C versus the 7.0% in the theory (and the numbers from this study.)
http://s21.postimg.org/5g73ffe87/Temps_vs_PCWV_Scatter_1958_Feb14.png
This feedback rate is enough to drop the climate sensitivity to 1.8C per doubling rather than 2.5-3.0C in the theory.
All water vapor studies from pro-global warming scientists cherrypick starting and ending timelines to take advantage of the ENSO conditions.
Guess I ought to wait until someone else takes this to bits, but it is really becoming tiresome.
“Radiative transfer”? If that was all that is involved I would not be here writing this. Don’t they know that the effect works in both directions? Eg cloudy days are cooler than sunny days? And at night, sure, it takes longer for the heat to escape if there is cloud overhead here at 19°S but it is still gone well before sunrise.
Question from a non-scientific learned person …
If, as some have said, the warming impact of increases in CO2 have been significantly overstated (thereby making CO2’s impact fairly low) does it therefore appear that a key driver of warming assuming a more “nature-driven” warming (ie., termination of the Little Ice Age circa mid-19th Century) is water and/or water vapor?
Many thanks for your insights.
Pete
Bill Illis says:
March 11, 2014 at 5:36 pm
Like, totally awesome, dude!
Actually, I’m surprised that IPeCaC´s assumption is even that close to observations (4.14% v. 7.0%).
Why is water vapor considered feedback to enhance the CO2 “greenhouse effect” when it is a “greenhouse gas” at concetrations much greater. The direct greenhouse effect of water vapor is probably at least an order of magnitude greater than any CO2 effect. Add clouds and it gets even more complex.
Hmmm.
They derive a short-term, all-in water vapor feedback of 2.2 W/Km^2. Now, doubling CO2 is equivalent to about 3.7 W/m^2 and results in about 1 K of temperature increase before feedbacks kick in. That means the water vapor positive feedback is (3.7+2.2)/3.7 = 1.6.
That is, a 1 K temperature increase from CO2 results in an additional warming of 0.6 K from water vapor feedback.
Put another way, CACC has been ‘nailed to its perch.’
Why is this positive feedback so much lower than previous claims?
Since they have found positive water vapor feedback based on measurements, did they also mention where the water vapor induced tropospheric hot spot is hiding? Perhaps below 2000m in the oceans?
“Determining the exact strength of the water vapor feedback, then, is incredibly important to limiting uncertainty in future climate change projections.”
Sorry, pet peeve of mine but risking being called a pointy headed nitpicker because I think it weakens an important post. Of course you don’t mean “incredibly important.”
“Important” by itself is sufficient. Or you could use “critical,” or “crucial.”
Oops, never mind. I missed who wrote this. My bad.
Bill Illis says:
March 11, 2014 at 5:36 pm
The temperature record has been fiddled upwards on the recent end and downwards on the earlier end (recent end constrained, thank goodness, by satellite measurements), particularly by Hansen who had a mission to get rid of the exasperating 1930s records in the USA in 1998 because he saw this El Nino as the last chance to get a new global temperature high. We seem fated to use this abused record. Hadcrut 4 was a way to exploit the incomplete coverage of the polar regions by satellite and the “amplification” permitted lifting the recent temps a bit as did a recent paper purporting to show that there was not ‘pause”. Willis with Ceres data showed the amplification was countered by lower heating in the tropics so the adjustment wasn’t necessary.
I think 4.14% water vapor increase is an index of the cooking the temperature record has taken. Probably, in reality, it represents 4.14/7.0 *1.0 degree Celsius as the amount of temp rise we are talking about. This works out to 0.59 degrees C temperature rise. Yeah, that’s about right they’ve jacked it up several tenths of a degree. I see that Clausius Clapeyron is going to be helpful when we come to undo the damage done by zealots. It also shows how naive it is to think you can fiddle with a part of such a complex system without screwing up other parts.
Since relative humidity is not going up:
http://www.climate4you.com/images/NOAA%20ESRL%20AtmospericRelativeHumidity%20GlobalMonthlyTempSince1948%20With37monthRunningAverage.gif
Since specific humidity is not going up:
http://www.climate4you.com/images/NOAA%20ESRL%20AtmospericSpecificHumidity%20GlobalMonthlyTempSince1948%20With37monthRunningAverage.gif
Someone should tell these guys…
“2.2 plus or minus 0.4 watts per square meter per degree Celsius”
Is that with an African or a European swallow’s tailwind ? Or both with a string?
The purported precision of these “global studies” is always hilarious and instructive.
Actually the plateau in temperatures is probably part of the screw up. If you raise these temps too steeply, you end up starting the plateau too early and making it too long. Let’s not let any of these linear thinkers undertake any geoengineering – the unintended consequences certain to occur could ruin a perfectly good planet.
Where exactly do clouds appear in Clausius Clapeyron? Or in models?
Let’s see now. Increased heating, more water vapor, more clouds, increased albedo, less heating.
Looks like negative feedback to me.
We should recognize that water vapor does go up with increased temperature (and down with decreased temperature). Specific Humidity does go up when it gets warmer. The tropics have far more water vapor in the atmosphere than does the poles. The Clausius Clapyeron equations are mostly right.
It is important to understand that climate science and the water vapor feedback is not one single feedback loop. It feeds back on itself so that there are several rounds of temperature increases which then leads to more water vapor which then leads to more water vapor increase which then …. and so on and so on. It really take a loop of about 11 feedbacks on feedbacks before the diminishing impacts set in and there are no more temperature impacts from increased water vapor.
11 feedbacks on feedbacks rather than 1.
So a very small change from 7.0% per 1.0C or 2.2 W/m2/K results in a big change in the eventual temperature change from a 1.2C increase in temperatures from a doubling of CO2 (if one assumes this was calculated correctly and I don’t necessarily believe that either).
But if one does accept the 1.2C from CO2 doubling, the X.X W/m2/K water vapor feedback value is then carefully chosen so that it does not result in a runaway greenhouse impact or a minimal greenhouse impact. Double the assumed water vapor feedback assumption to 4.4 W/m2/K and one gets 35C of temperature change per doubling of CO2. Drop it by half to 1.1 W/m2/K and one gets just 1.6C of temperature increase per doubling.
So a small change in the way the real Earth(tm) responds to GHG increases is indeed a very important change in the eventual warming.
Make clouds a negative -0.75 W/m2/K (instead of a positive 0.75) and drop the water vapor feedback to 4.14% per 1.0C (as the actual data shows), then the climate sensitivity is only 1.1C per doubling.
Climate science did these little feedback assumption calculations long ago and decided to keep all the assumptions at rates which would result in 3.0C per doubling. They then built these numbers into their climate models.
It is important to find out how the real Earth(tm) responds because it is a make or break on the eventual warming. Climate science likes to reinforce itself rather than find out what’s really happening. And they are willing to adjust temperature records (which is why I use the lower troposphere non-adjusted ones) and why they cherrypick timelines to keep the feedback assumptions at the right level. Much money and reputation is at stake.
fhhaynie says: @ur momisugly March 11, 2014 at 5:51 pm
Why is water vapor considered feedback to enhance the CO2 “greenhouse effect” when it is a “greenhouse gas” at concetrations much greater….
>>>>>>>>>>>>>>>
Because CO2 is a wimp. Only by adding in H2O as a ‘Feedback’ of CO2 can you get Catastrophic Global Warming and even then you have to completely ignore the fact H2O unlike CO2 changes phases thereby giving you Willis’s Thunderstorm Thermostats
Combined with a radiative transfer model,
*****
Model based upon what?
The same old pseudo-science. Neatly summarised by the following:
http://kitshaper.files.wordpress.com/2011/08/cga0226l1.jpg
In average, the surface cooling by evaporation is greater than the claimed water vapor GHE. So, H2O is cooling the Earth’s surface overall (net cooling effect). Even the consensus agrees with this.
Gordon, Jonko & Forster ignore clouds, never mention ’em, but posters at “Watts Up With That” bring ’em up right way. Why do you suppose that is?
Berenyi
AIRS is observations. In fact you might want to familiarize yourself with the sensors.
Launched in 2002 it will fly until 2020.
Allegedly increased water vapour means increased latent heat of vapourisation shunting energy to the upper atmosphere and out into space a la Trenberth diagram as part of an energy flow about 200 times greater than the 0.4 Watts/sq metres from C02. 1 kg of water evaporated can cool about 2000 kg of air by 1˚C. Sound very much like a negative feedback to me and that is before we talk about clouds.
The paper sounds like more good for a goose therefore good for propaganda to me.