How can Richard Lindzen continue to defend his IRIS hypothesis when the water vapor feedback is positive?

Question

According to the IRIS hypothesis, precipitation efficiency during deep convection events will increase as the planet warms. This, in turn, will significantly reduce water vapor content in the upper troposphere. High cirrus cloud cover will then decrease, leading to an increase in ORL. 

In a recent paper, Richard Lindzen made the following claim in support of the IRIS hypothesis:

“Lindzen and Choi [2009] studied variations in the outgoing radiative fluxes with respect to changes in the average tropical temperature in intraseasonal scales. A total negative feedback was deduced from the outgoing long- wave response of the tropics. If a strong positive water vapor feedback is realistic [e.g., Dessler et al., 2008], then the combined effect of water vapor feedback and lapse rate feedback must be more than compensated by a strong unknown process acting on modifying the longwave flux. This process cannot be distinguished from the bulk of the longwave response in the analysis by Lindzen and Choi [2009], but it most likely resides in the combined behavior of clouds and water vapor in the tropics. This leaves open the possibility that a negative feedback such as the iris is operating in the present climate.”
http://www.dgf.uchile.cl/~ronda/Geologia/ronandlin10a.pdf
 
To me, it seems that the IRIS hypothesis cannot be correct. Dessler (2008) concluded that, “At all altitudes...global-average specific humidity was higher during the warmer periods, with the difference growing with altitude.” 
http://geotest.tamu.edu/userfiles/216/Dessler2008b.pdf

However, as mentioned previously, the IRIS hypothesis predicted that tropospheric water vapor content would actually decrease. 

How can Lindzen continue to defend his IRIS hypothesis when he also supports Dessler's conclusions?

bob326 · Accepted Answer

Well, it's a little more nuanced than that. Dessler & Zhang (2008) did indeed find a positive water vapor feedback consistent with constant RH overall, but the vertical profile of RH was not conserved, decreasing slightly in the tropical upper troposphere. Specific humidity increased, but both the direct radiative effects of WV and cloud coverage is more closely tied into relative humidity.

In any case, Lindzen's IRIS *could* still be consistent with DZ 2008. Cirrus detrainment is determined more by the amount of time for which condensation can occur during DC events, since RH is near to the saturation value in the tropics below the boundary level anyway. Too long and you get rain droplets, too short and the cloud droplets freeze in the UT forming high thin Cirrus. The whole issue is somewhat convoluted, and upon re-reading my answer to your last question I made it sound as though the IRIS effect hinged upon the WV feedback, but that's not necessarily the case.

This ignores the theoretical problems with IRIS highlighted by e.g. Hartmann & Michelson (2002) [1], as well as observational issues found by Lin et al. (2002) [2] and Su et al. [3] among many others.

Anonymous · Answer

Richard Lindzen, along with Roy Spencer, has long been considered to be one of the last remaining true skeptics.

Of course, since the IRIS hypothesis supposes that water vapor is a negative feedback, Dessler's finding to the effect that water vapor is a positive feedback falsifies the IRIS hypothesis. If no evidence contrary to the conclusions of Dessler's paper can be found, Lindzen would have to change his views. If Lindzen refuses to acknowledge the evidence, he would no longer be a skeptic, but a denier.

Dana1981 · Answer

The short answer is that Richard Lindzen is an intellectually dishonest denier.

First off, the study he refers to - Lindzen and Choi 2009 - is absurdly flawed.  It was torn to shreds by several subsequent studies from other climate scientists.  Even Lindzen admitted it contained many errors, but he claimed he had addressed those errors, and they didn't change his results significantly.  Except he couldn't get his revised paper published, which means he failed to adequately respond to the criticisms.  To continue referencing this abysmal paper is flat-out dishonest.

There have also been several studies which have demolished the Iris hypothesis.  Back in 2006, in an interview Lindzen basically admitted the hypothesis was wrong - he got upset that the interviewer even brought it up, calling it old news.  Yet now he's still trying to argue that it's correct?  He's trying to defend one wrong paper with another wrong paper!

So how can Lindzen make this contradictory argument?  Because he doesn't care about being correct or honest or a good scientist, he just wants to somehow find an argument that we dont have to worry about global warming.  It's the same thing as I described in the article below, where he builds one wrong argument on top of the next, on top of the next, until he's got this beautifully wrong house of cards put together.

The only way to defend a wrong argument is with another wrong argument.

Anonymous · Answer

very interesting question

How can Richard Lindzen continue to defend his IRIS hypothesis when the water vapor feedback is positive?

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