Atmospheric water vapour is a feedback (not forcing) - on Watts and Eschenbach #AGU16 poster

Willis Eschenbach has a poster at AGU16, to which Anthony Watts added his name. Anthony's now written a blog article about it (archived here). Actually, Anthony put his name first although I strongly suspect he doesn't have a clue what the poster is all about.

They haven't made the poster available on the AGU16 website, or not at the time of this article. It is downloadable on Anthony's blog at WUWT, here.  He's also made available what he calls "data and code". The file is 500 MB or so, therefore I won't be downloading it till I get home in 20 hours or so.

There are a few points I'll make:

• The poster is based on a couple of blog articles by Willis Eschenbach at WUWT, including the one I wrote about here.
• Willis Eschenbach still doesn't know the difference between a forcing and a feedback (more below). Nor does Anthony Watts.
• Their poster supports what real scientists tell us, that there's more water vapour in the air because of global warming.
• Most of the data they use is ocean only, not land.
• They seem happy to rely on RSS data, while disparaging it elsewhere.
• They seem happy with lots of data carefully collected and analysed by climate scientists, despite calling it fraudulent elsewhere, and despite WUWT-ers wanting to stop all research.

To demonstrate that Willis and Anthony don't know the difference between forcing and feedback, at the bottom of the third panel of the poster, Willis wrote:

There is a clear trend in the TPW data. The total change over the period is ~ 1.5 kg/m2, centered around the long-term mean of 28.7 kg/m2. Utilizing the relationship between water content and atmospheric absorption derived above, this indicates an increase in downwelling radiation of 3.3 W/m2 over the period. Note that this 3.3 W/m2 increased forcing from the long-term increase in water vapor since 1988 is in addition to the IPCC-claimed 2.3 W/m2 increase since 1750 in all other forcings (see Figure SPM-5, IPCC AR5 SPM5). The IPCC counts as forcings the long-term changes in the following: CO2, CH4, Halocar-bons, N2O, CO, NMVOC, NOx, mineral dust, SO2, NH3, organic carbon, black carbon, land use, and changes in solar irradiance, but not the long-term changes in water vapor.

Key finding
This leads us to a curious position where we have had a larger change in forcing from water vapor since 1988 than from all the other IPCC-listed forcings since 1750.

Thing is of course that the statements in the IPCC report are about forcing. The increase in water vapour is a feedback, or response, to that forcing. This is what is stated in the IPCC AR5 SPM report, above the reference to Figure SPM.5, to which Willis and Anthony referred. I've emphasised the parts Willis and Anthony either didn't read or failed to understand:

Natural and anthropogenic substances and processes that alter the Earth's energy budget are drivers of climate change. Radiative forcing14 (RF) quantifies the change in energy fluxes caused by changes in these drivers for 2011 relative to 1750, unless otherwise indicated. Positive RF leads to surface warming, negative RF leads to surface cooling. RF is estimated based on in-situ and remote observations, properties of greenhouse gases and aerosols, and calculations using numerical models representing observed processes. Some emitted compounds affect the atmospheric concentration of other substances. The RF can be reported based on the concentration changes of each substance15. Alternatively, the emission-based RF of a compound can be reported, which provides a more direct link to human activities. It includes contributions from all substances affected by that emission. The total anthropogenic RF of the two approaches are identical when considering all drivers. 

In other words, forcing up (higher temperature) causes a feedback of more atmospheric water vapour, and the combined effect is included in the chart below. Correction: The chart below isn't the combined effect of forcing and feedback, it's just the radiative forcing.

Figure 1 | Radiative forcing estimates in 2011 relative to 1750 and aggregated uncertainties for the main drivers of climate change. Values are global average radiative forcing (RF15) partitioned according to the emitted compounds or processes that result in a combination of drivers. The best estimates of the net radiative forcing are shown as black diamonds with corresponding uncertainty intervals; the numerical values are provided on the right of the figure, together with the confidence level in the net forcing (VH – very high, H – high, M – medium, L – low, VL – very low). Albedo forcing due to black carbon on snow and ice is included in the black carbon aerosol bar. Small forcings due to contrails (0.05 W m–2, including contrail induced cirrus), and HFCs, PFCs and SF6 (total 0.03 W m–2) are not shown. Concentration-based RFs for gases can be obtained by summing the like-coloured bars. Volcanic forcing is not included as its episodic nature makes is difficult to compare to other forcing mechanisms. Total anthropogenic radiative forcing is provided for three different years relative to 1750. For further technical details, including uncertainty ranges associated with individual components and processes, see the Technical Summary Supplementary Material. {8.5; Figures 8.14–8.18; Figures TS.6 and TS.7}. Source: IPCC Summary for Policymakers Fig SPM.5

The IPCC reports discuss effects such as the increase in atmospheric water vapour as "responses" to the forcing, or feedback.

I'm out right now, and all day today. I won't be back for another 12 hours or more, but I thought it might be useful to get this article up now. I'll maybe do more on the subject later. Meanwhile, feel free to expand in the comments.