Here’s an interesting paper that breaks with consensus. The only problem is that it is being ignored for the most part by the mainstream climate community, even going so far as to having a debate over the paper’s source of data (NCEP reanalysis of radiosonde data) and declaring the data to be too “iffy”. You can read all about that debate at Climate Audit called “A peek behind the curtain
“. It is a firsthand account of the attempt at publishing from one of the authors, Garth Paltridge. Here is how he characterized the debate at a conference:
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.
Since most of the objections seemed to be coming from GISS, who has a surface data set that one could also describe as “iffy”, I find their argument rather humorous.
What is really interesting though is this graph presented in comments at CA by Ken Gregory:
“The relevant discussion of the water vapour effect from the IPCC Fourth Assessment Report (Chapter 8 page 632):
The radiative effect of absorption by water vapour is roughly proportional to the logarithm of its concentration, so it is the fractional change in water vapour concentration, not the absolute change, that governs its strength as a feedback mechanism. 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 220.127.116.11). 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.
This means that changes in specific humidity in the upper troposphere (300 – 700 mb) may be very significant even though the amount of water vapour there is low due to the cold temperatures.
If relative humidity remains constant, CO2 induced warming would cause increasing specific humidity and a strong positive feedback. But if relative humidity is actually falling (due to water vapour being displaced by CO2 as per Miskolczi) then water vapour may cause a negative feedback. The specific humidity has declined dramatically in 2008 at ALL levels in the troposphere.
I do not know the accuracy of the NCEP reanalysis data on upper tropospheric humidity, but the direct measurement of humidity by weather balloons seems preferable to the very indirect determination from satellite data.”
I agree. Here is more on the paper and it’s conclusions. – Anthony
New Paper Suggests Long-Term Water Vapour Feedback is Negative
(1) Environmental Biology Group, RSBS, Australian National University, GPO Box 475, Canberra, ACT, 2601, Australia
(2) Johns Hopkins University, Baltimore, MD, USA
(3) Centre for Australian Weather and Climate Research, Hobart, TAS, Australia
The Abstract states:
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.
The paper concludes:
It is of course possible that the observed humidity trends from the NCEP data are simply the result of problems with the instrumentation and operation of the global radiosonde network from which the data are derived. The potential for such problems needs to be examined in detail in an effort rather similar to the effort now devoted to abstracting real surface temperature trends from the face-value data from individual stations of the international meteorological networks. As recommended by Elliot and Gaffen (1991) in their original study of the US radiosonde network, there needs to be a detailed examination of how radiosonde instrumentation, operating procedures, and recording practices of all nations have changed over the years and of how these changes may have impacted on the humidity data.
In the meantime, it is important that the trends of water vapor shown by the NCEP data for the middle and upper troposphere should not be “written off” simply on the basis that they are not supported by climate models—or indeed on the basis that they are not supported by the few relevant satellite measurements. There are still many problems associated with satellite retrieval of the humidity information pertaining to a particular level of the atmosphere—particularly in the upper troposphere. Basically, this is because an individual radiometric measurement is a complicated function not only of temperature and humidity (and perhaps of cloud cover because “cloud clearing” algorithms are not perfect), but is also a function of the vertical distribution of those variables over considerable depths of atmosphere. It is difficult to assign a trend in such measurements to an individual cause.
Since balloon data is the only alternative source of information on the past behavior of the middle and upper tropospheric humidity and since that behavior is the dominant control on water vapor feedback, it is important that as much information as possible be retrieved from within the “noise” of the potential errors.