Water vapor feedback followup?

This is an interesting question, and I'm actually organizing a seminar on the subject of water vapor and global circulation next quarter and I'll point people toward these references. The constant relative humidity assumption (based on models) is a bit mysterious and definitely bears further looking into.

While I'm a user of reanalysis myself, I would be cautious on using q globally from reanalysis. Many places in the world are very far from radiosonde observations and the quality will suffer. I'm not sure what other humidity data they've assimilated into the NCEP reanalysis, but I don't think there would be that much else going back to 1973. The question I wonder (I've only skimmed the Paltridge et al paper so far) is why didn't they just use the global radiosonde data directly? It's nice to have gridded data set for the whole world that's been run through a numerical model, but in areas where data is sparse I think reanalysis is still going to be shaky.

To be honest, though, even the radiosonde data can have problems. Bob Maddox has been complaining for years about the switch to the Sippican sounders that are currently being used. I think the prospect is much better for excellent water vapor data going forward than it is looking backward. Personally I'm trying to reconstruct integrated water vapor datasets looking backward at archived GPS delays, but there is very little data once you get back to the early 90's.

Unfortunately I've been quite busy lately and haven't had as much time to read these resources as I'd like. From what I have read, it seems as though Dessler is confident that most studies agree that water vapor will be a net postive feedback. The Paltridge paper you link appears to disagree, with some caveats about the data quality.

This is why water vapor remains one of the largest uncertainties in climate models. It's a difficult effect to predict, but from what I've read I agree with Dessler's conclusion that the majority of studies have concluded it will be a fairly strong positive feedback.

2 key quotes from their abstract:

"The upper-level negative trends in q are inconsistent with climate-model calculations and are largely (but not completely) inconsistent with satellite data. "

Why is it inconsistent?

"It is accepted that radiosonde-derived humidity data must be treated with great caution, particularly at altitudes above the 500 hPa pressure level. "

There's a variety of lines of evidence on the positive water vapor feedback that go beyond the direct observations (i.e. Dessler studies).

http://www.realclimate.org/index.php?p=142

More info on radiosonde data, and several studies that reveal large inconsistencies.

http://www.realclimate.org/index.php/archives/2008...

EDIT

"What exactly are you saying? "go beyond the direct observations"? Sure, there is theoretical support. But direct observations are far more interesting."

From my link:

"How do we know that the magnitude of this feedback is correctly simulated? A good test case is the response to the Pinatubo eruption. This caused cooling for up to 3 years after the eruption - plenty of time for water vapour to equilibriate to the cooler sea surface temperatures. Thus if models can simulate the observed decrease of water vapour at this time, it would be a good sign that they are basically correct. A good paper that demonstrated this was Soden et al (2002) (and the accompanying comment by Tony DelGenio). They found that using the observed volcanic aerosols as forcing the model produced very similar cooling to that observed. Moreover, the water vapour in the total column and in the upper troposphere decreased in line with satellite observations, and helped to increase the cooling by about 60% - in line with projections for increasing greenhouse gases."

Your Dessler article goes into other lines of evidence.

You wrote:

"Yes, there were some large problems with the Douglass study as your last link points out. And yes, you must be careful when relying on radiosonde data, but radiosonde data is still good data"

Why would you conclude it's good data, given the various large problems found, many still outstanding and unresolved? It was certainly enough to warrant a large caveat in the abstract of the study based on it - specifically with regards to the height range they were deriving humidity from, and contradicted by a variety of other evidence based on more sound data and observations (also mentioned in the abstract). Additionally, radiosonde data was designed to detect short-term trends, and is less robust over long periods of time, which the study looks at.

Here are some comments from Dessler on water vapor feedback in climate models. For contrarians: even Spencer agrees.

http://gristmill.grist.org/story/2009/2/23/18157/0...

As a sidenote, the lead author of the study cited above (Garth Paltridge) is a member of this group.

http://www.sourcewatch.org/index.php?title=Natural...

http://www.nrsp.com/scientists.html

<sigh>...and I was assuming good faith.

EDIT2

"Why would you no longer assume good faith? The paper was still published in a legitimate peer reviewed journal. "

True - which is why I'm taking the time to address it. But remember, peer review is not a sufficient condition for reliability.

http://www.realclimate.org/index.php?p=111

I question why the author would attempt to make inferences from unreliable data. Since they included the strong caveat and showed it was inconsistent with other data, that might have been enough to pass peer review. It's also enough to be quite cautious when looking at this study.

I find it interesting that alarmists will inevitably take the worst evidence and conjecture as fact yet find any reason whatsoever to discount things which might jeopardize their theory that we are harmfully warming the planet. They are not looking for the truth but advocating a cause. That is certainly not a very good scientific attitude. Skepticism is the heart of science.

I sure got wacked on that question from Dana. I had 5 down arrows before I could edit the thing. It always fascinates me how those down arrows seem to come in packs.