On Feb 26, Garth Paltridge, Albert Arking and Michael Pook’s report on a re-examination of NCEP reanalysis data on upper tropospheric humidity was published online by Theoretical and Applied Climatology. Upper tropospheric humidity is a critical topic in assessing the strength of water vapor feedbacks – knowledge that is essential to understand just how much temperature increase can be expected from doubled CO2. Paltridge and Arking are both senior climate scientists with lengthy and distinguished publication records. They reported:
The National Centers for Environmental Prediction (NCEP) reanalysis data on tropospheric humidity are examined for the period 1973 to 2007. It is accepted that radiosonde-derived humidity data must be treated with great caution, particularly at altitudes above the 500 hPa pressure level. With that caveat, the face-value 35-year trend in zonal-average annual-average specific humidity q is significantly negative at all altitudes above 850 hPa (roughly the top of the convective boundary layer) in the tropics and southern midlatitudes and at altitudes above 600 hPa in the northern midlatitudes. It is significantly positive below 850 hPa in all three zones, as might be expected in a mixed layer with rising temperatures over a moist surface. The results are qualitatively consistent with trends in NCEP atmospheric temperatures (which must also be treated with great caution) that show an increase in the stability of the convective boundary layer as the global temperature has risen over the period. The upper-level negative trends in q are inconsistent with climate-model calculations and are largely (but not completely) inconsistent with satellite data. Water vapor feedback in climate models is positive mainly because of their roughly constant relative humidity (i.e., increasing q) in the mid-to-upper troposphere as the planet warms. Negative trends in q as found in the NCEP data would imply that long-term water vapor feedback is negative—that it would reduce rather than amplify the response of the climate system to external forcing such as that from increasing atmospheric CO2. In this context, it is important to establish what (if any) aspects of the observed trends survive detailed examination of the impact of past changes of radiosonde instrumentation and protocol within the various international networks.
A few days earlier on Feb 20, Dessler and Sherwood published a review article in Science on upper tropospheric humidity. This was accompanied by a podcast and a blog article at Grist here . They reported:
Interestingly, it seems that just about everybody now agrees water vapor provides a robustly strong and positive feedback
They made no mention of the pending Paltridge et al results.
OK, climate scientists disagree. What else is new. However, today you get a little peek behind the curtains, courtesy of Garth Paltridge who sends in the following account of the handling (and rejection) of their article at Journal of Climate.
Garth Paltridge writes:
LOADED DICE IN THE CLIMATE GAME
Back in March of 2008, three of us sent off a manuscript to the Journal of Climate. It was a straightforward paper reporting the trends of humidity in the middle and upper troposphere as they (the trends) appear at face value in the NCEP monthly-average reanalysis data. NCEP data on atmospheric behaviour over the last 50 years are readily available on the web and are something of a workhorse for much modern research on meteorology and climate.
The paper did two things:
(1) It pointed out that, according to the NCEP data, the zonal-average tropical and mid-latitude humidities have decreased over the last 35 years at altitudes above the 850mb pressure level – that is, in the middle and upper troposphere, roughly above the top of the convective boundary layer. NCEP humidity information derives ultimately from the international network of balloon-borne radiosondes. And one must say immediately that radiosonde humidity data have more than their fair share of problems. So does the NCEP process of using an operational weather forecasting model to integrate the actual measurements into a meteorologically coherent set of data presented on a regular grid.
(2) It made the point (not an original point, but on the other hand one that is not widely known even among the cognoscenti) that water vapour feedback in the global warming story is very largely determined by the response of water vapour in the middle and upper troposphere. Total water vapour in the atmosphere may increase as the temperature of the surface rises, but if at the same time the mid- to upper-level concentration decreases then water vapour feedback will be negative. (There are hand-waving physical arguments that might explain how a decoupling such as that could occur).
Climate models (for various obscure reasons) tend to maintain constant relative humidity at each atmospheric level, and therefore have an increasing absolute humidity at each level as the surface and atmospheric temperatures increase. This behaviour in the upper levels of the models produces a positive feedback which more than doubles the temperature rise calculated to be the consequence of increasing atmospheric CO2.
The bottom line is that, if (repeat if) one could believe the NCEP data ‘as is’, water vapour feedback over the last 35 years has been negative. And if the pattern were to continue into the future, one would expect water vapour feedback in the climate system to halve rather than double the temperature rise due to increasing CO2.
Satellite data from the HIRS instruments on the NOAA polar orbiting satellites tend (‘sort of’, only in the tropics, and only for part of the time) to support the climate model story. The ‘ifs and buts’ of satellite information about upper tropospheric humidity are of the same order as that from balloon radiosondes.
Anyway, our paper concluded by suggesting that, in view of the extreme significance of upper-level humidity to the climate change story, the international radiosonde data on upper-level humidity should not be ‘written off’ without a serious attempt at abstracting the best possible humidity signal from within the noise of instrumental and operational changes at each of the relevant radiosonde stations. After all, we are not exactly over-endowed with data on the matter. The attempt would be similar in principle to the current efforts at abstracting a believable global warming signal from the networks of surface-temperature observations.
Suffice it to say that after 3 or 4 months the paper was knocked back. This largely because of an unbelievably vitriolic, and indeed rather hysterical, review from someone who let slip that
“the only object I can see for this paper is for the authors to get something in the peer-reviewed literature which the ignorant can cite as supporting lower climate sensitivity than the standard IPCC range”.
We argued a bit with the editor about why he took notice of such a review. We are not exactly novices in the research game, and can say with reasonable authority that when faced with such an emotive review the editor should simply have ignored it and sent the paper off to someone else. The argument didn’t get far. In particular we couldn’t get a guarantee that a re-submission would not involve the same reviewer. And in any event the conditions for re-submission effectively amounted to a requirement that we first prove the models and the satellites wrong.
A couple of weeks after the knock-back, and for unrelated reasons, two of us went to a small workshop on water vapour held at LDEO in New Jersey, whereat we told the tale. The audience was split as to whether the existence of the NCEP trends in humidity should be reported in the literature. Those ‘against’ (among them a number of people from GISS) simply said that the radiosonde data were too ‘iffy’ to report the trends publicly in a political climate where there are horrible people who might make sinful use of them. Those ‘for’ simply said that scientific reportage shouldn’t be constrained by the politically correct. The matter was dropped. I found after the event that the journal editor had come (I think specifically) to hear the talk. He didn’t bother to introduce himself.
I guess the story doesn’t amount to much. Perhaps it is significant only in that it shows how naïve we were to imagine that climate scientists might welcome the challenge to examine properly and in detail even the smell of a possibility that global warming might not be as bad as it is made out to be. Silly us.
After some kerfuffle, the paper was accepted by “Theoretical and Applied Climatology” and appeared on February 26 on the journal’s web site. (One can if so inclined, and if one has personal or institutional access to the journal, find it here). We presume it will be ignored. Being paranoiac from way back, we wonder at the happy chance by which a one-page general-interest article appeared in ‘Science’ on February 20. With some self-referencing, it extolled the virtue of the latest modelling research, and of new(?) satellite observations of short-term, large amplitude, water vapour variability, which (say the authors) strongly support model predictions of long-term positive water vapour feedback. Well, maybe. It would be easy enough to argue against that conclusion. The paranoia arises because of another issue. We know that at least one of the authors is well aware of the contrary story told by the raw balloon data. But there is no mention of it in their article.