image Figure 4 from Vonder Haar et al 2012

As promised by Tom Vonder Haar; see the posts

“Water Vapor Feedback Still Uncertain” By Marcel Crok

Statement By Vonder Haar Et Al 2010 on Using Existing [NASA Water Vapor] NVAP Dataset (1988 – 2001) for Trends

The new dataset covering 20+ years will be available to the public in 2012 or 2013.

The initial results are now ready as reported in the paper

Vonder Haar, T. H., J. Bytheway, and J. M. Forsythe (2012), Weather and climate analyses using improved global water vapor observations,

Geophys. Res. Lett.,doi:10.1029/2012GL052094, in press.

The abstract reads [highlight added]

The NASA Water Vapor Project (NVAP) dataset is a global (land and ocean) water vapor dataset created by merging multiple sources of atmospheric water vapor to form a global data base of total and layered precipitable water vapor. Under the NASA Making Earth Science Data Records for Research Environments (MEaSUREs) program, NVAP is being reprocessed and extended, increasing its 14-year coverage to include 22 years of data. The NVAP-MEaSUREs (NVAP-M) dataset is geared towards varied user needs, and biases in the original dataset caused by algorithm and input changes were removed. This is accomplished by relying on peer reviewed algorithms and producing the data in multiple “streams” to create products geared towards studies of both climate and weather. We briefly discuss the need for reprocessing and extension, steps taken to improve the product, and provide some early science results highlighting the improvements and potential scientific uses of NVAP-M.

The current paper is not the final word on this subject. The end of the paper reads

The results of Figs. 1 and 4 have not been subjected to detailed global or regional trend analyses, which will be a topic for a forthcoming paper. Such analyses must account for the changes in satellite sampling discussed in the supplement. Therefore, at this time, we can neither prove nor disprove a robust trend in the global water vapor data.

However, the figure at the top of this post, if it turns about to be robust, raises fundamental issues with respect to the ability of global climate models to skillfully model the role of humans in altering the climate. Indeed, the Vonder Haar et al 2012 provides further support to the conclusion by De-Zheng Sun in the paper

Sun, D.-Z., Y. Yu, and T. Zhang, 2009: Tropical Water Vapor and Cloud Feedbacks in Climate Models: A Further Assessment Using Coupled Simulations. J. Climate, 22, 1287-1304

that I posted on in

Tropical Water Vapor and Cloud Feedbacks in Climate Models: A Further Assessment Using Coupled Simulations by De-Zheng Sun, Yongqiang Yu, and Tao Zhang

As part of their conclusions, they wrote

“The extended calculation using coupled runs confirms the earlier inference from the AMIP runs that underestimating the negative feedback from cloud albedo and overestimating the positive feedback from the greenhouse effect of water vapor over the tropical Pacific during ENSO is a prevalent problem of climate models.

While De-Zheng was reluctant to relate his findings to multi-decadal global climate model simulations of the role of humans in the climate system, the new Vonder Haar et al 2012 paper provides further support that the water vapor feedback is overstated by the IPCC models.