Tropospheric hotspot and positive feedback?

Sounds like he's channeling Roy Spencer's argument, but rather confused about it.

"One of the most robust feedback relationships across the IPCC climate models is that those models with the strongest positive water vapor feedback have the strongest negative lapse rate feedback (which is what the “hot spot” would represent). So, the lack of this negative lapse rate feedback signature in the satellite temperature trends could be an indirect indication of little (or even negative) water vapor feedback in nature."

http://www.drroyspencer.com/2010/09/five-reasons-w...

Problem with Spencer's argument is that there is empirical data showing that the water vapor feedback is positive.

"although there continues to be some uncertainty about its exact magnitude, the water vapor feedback is virtually certain to be strongly positive, with most evidence supporting a magnitude of 1.5 to 2.0 W/m2/K, sufficient to roughly double the warming that would otherwise occur."

http://www.see.ed.ac.uk/~shs/Climate%20change/Data...

So unless the guy wants to take a possible correlation in climate models over empirical observations (and last I checked, deniers usually think models are worthless), his argument is bunk.

*edit @ eric* "Proponents...use other studies to suggest that there is a positive water vapour feedback"

Yes, I can't understand why we would use direct measurements of water vapor to calculate the water vapor feedback. What a bunch of frauds!

I recommend reading the summary paper I linked above, from Dessler and Sherwood (published several years after the last IPCC report, during which time we've learned a lot about the water vapor feedback). It's only 2 pages long and addresses the lapse rate feedback. Some more excerpts:

"the sum of the two feedbacks [water vapor and lapse rate] is insensitive to errors in predicted warming of the upper troposphere, and to quantify the sum accurately, one only needs to know how relative humidity (the ratio of specific humidity to that in a saturated condition) changes as the climate warms....Both observations and models suggest that the magnitude of the water vapor feedback is similar to that obtained if the atmosphere held relative humidity constant everywhere....evidence for the water vapor feedback—and the large future climate warming it implies—is now strong."

*edit* Eric, read your own sources more carefully. Solomon specifically discusses a *short-term* decrease in *stratospheric* water vapor. And I didn't say anything about opinions, I'm talking about empirically observed data. You're the one referencing opinions (i.e. Zagoni).

The poster is indeed correct. From ar4-wg1-chapter8.p.632

" Calculations with GCMs suggest that water vapour remains at an approximately constant fraction of its saturated value (close to unchanged relative humidity (RH)) under global-scale warming (see Section 8.6.3.1). Under such a response, for uniform warming, the largest fractional change in water vapour, and thus the largest contribution to the feedback, occurs in the upper troposphere. In addition, GCMs find enhanced warming in the tropical upper troposphere, due to changes in the lapse rate (see Section 9.4.4). This further enhances moisture changes in this region, but also introduces a partially off setting radiative response from the temperature increase, and the net effect of the combined water vapour/lapse rate feedback is to amplify the warming in response to forcing by around 50% (Section 8.6.2.3). The close link between these processes means that water vapour and lapse rate feedbacks are commonly considered together."

We know that clouds and water vapour are closely related. It is also commonly acknowledged by climate scientists that clouds are poorly understood. But what will happen to this water vapour? Will it turn into clouds that will act as a negative feedback? Is the lack of a hotspot due to clouds acting a negative feedback? The notion that the role of water vapour is greatly understood, but clouds are not, is odd.

Proponents downplay the lack of a hotspot by saying that there is problems with both the satellite and balloon data, and use other studies to suggest that there is a positive water vapour feedback. If you think you are being scientific by only looking at data that supports your theory and ignoring those that do not, downplaying the uncertainties and still say you believe you are close to 100% correct, then go right ahead.

Edit to Dana: One person's opinion does not make it fact. Susan Solomon found that water vapour decline during this past decade:

"Observations from satellites and balloons show that stratospheric water vapor has had its ups and downs lately, increasing in the 1980s and 1990s, and then dropping after 2000. The authors show that these changes occurred precisely in a narrow altitude region of the stratosphere where they would have the biggest effects on climate."

http://www.noaanews.noaa.gov/stories2010/20100128_...

Miklós Zágoni, who produced the hypothesis that the greenhouse effect always remains constant, back up his hypothesis by stating that humidity has declined over the past couple of decades.

Like I said, there is evidence for and against. You are denying that there is evidence against it.

The hotspot is a predicted consequence of more water vapor making its way aloft in the tropical troposphere as the surface warms. There is conflicting evidence as to its existence, but if the hotspot was not detected, it would mean both a less positive water vapor feedback and a less negative to even slightly positive lapse rate feedback.

Given the issues with observed temperature profile trends in the tropical troposphere, measurements of water vapor content itself might yield a better understanding of the water vapor feedback. The study below confirms that, as the troposphere warms, the moisture content in the upper troposphere also increases in such a way that is consistent with little change in relative humidity, indicating a strongly positive feedback.

Eric

"Miklós Zágoni, who produced the hypothesis that the greenhouse effect always remains constant, back up his hypothesis by stating that humidity has declined over the past couple of decades."

Yes, and Zagoni uses the NCEP-NCAR reanalysis to do so. The fact that there are *known* issues with the NCEP reanalysis -- changes in spatio-tempero-resolution, improving observing systems, large model bias -- that lead to spurious trends in humidity data, and that the NCEP data is in conflict with all other observational datasets including more modern reanalysis and satellites should lead most people to question its accuracy. This isn't simply a case of "warmies ignoring data that conflicts with their ideology", but a legitimate argument for why NCEP shouldn't be used for long-term global humidity trends.

Zagoni/Misklozci's supposed "proof" of a constant greenhouse effect using an inaccurate dataset and a physically irrelevant parameter like the "greenhouse optical depth" (among other issues) is not convincing.

Never having had a discussion on YouTube I don’t know what that involves, if it’s in written format are you able to copy and paste the salient points of the conversation as it would help to be able to put into context what the other guy is talking about.

As Dawei and Dana have said, it sounds like he’s getting confused – badly confused.

The whole notion of the causes and effects of a tropospheric hotspot usually gets confused when people talk about it, in reality it’s probably not even a TH they’re talking about. A TH, such as it is, is consequential to the ALR, there are both pos and neg feedbacks but of such a low order as to be inconsequential.

This sounds like the sort of discussion where the other guy has gone off on a tangent after digging himself into a hole.

I think he's confused. The positive feedback is due to a global increase in specific humidity, which can already be observed:

http://hadobs.metoffice.com/hadcruh/

The existence of the water vapor feedback does not depend on the tropospheric hot spot signature. Skeptics love to talk about the hot spot because they think it proves that AGW is wrong, when in reality a hot spot would be expected with any type of warming, no matter what the driver is.

Goobley **** double talk by a globat warmist, They think it make them sound intelligent, only fools the ignorant