Dire predictions of global warming all rely on positive feedback from water vapor. The argument goes that as surface temperatures rise so more water will evaporate from the oceans thereby amplifying temperatures because H2O itself is a strong GHG. Climate models all assume net amplification factors of between 1.5 and 6. But in the real world has the water content of the atmosphere actually been increasing as predicted?

NASA have just released their latest NVAP-M survey of global water content derived from satellite data and radio-sondes over the period from 1988 to 2009. This new data is explicitly intended for climate studies . So lets take a look at the comparison between actual NVAP-M atmospheric H2O levels and those of CO2 as measured at Mauna Loa. I have extracted all the daily measurement NVAP-M data and then calculated the global average. Figure 1 shows the running 30 day average of all the daily data recorde between 1988 and 2009 inclusive. The 365 day (yearly) running average is also shown. Plotted on the right hand scale are the Mauna Loa CO2 concentration data in red over the same period.

There is indeed some correlation in the data from 1988 until 1998, but thereafter the two trends diverge dramatically. Total atmospheric water content actually falls despite a relentless slow rise in CO2. This fall in atmospheric H2O also coincides with the observed and now widely accepted stalling of global temperatures over the last 16 years. All climate models (that I am aware of) predict exactly the opposite, so something is clearly amiss with theory. Is it not now time for “consensus” climate scientists perhaps to have a rethink ?

more to follow…

My thanks to Ken Gregory for help with the data. The conversion from NetCDF was a bit of a nightmare ! NASA NVAP-M data is available here. Thanks to NASA Water Vapor Project-Measures (NVAP-M) team.

update 22/4: There is no inherent reason why atmospheric water content should be correlated with CO2 content. However, models typically assume a constant relative humidity so that if surface temperatures rise (AGW) then so does the total H2O content in the atmosphere. This post highlights the lack of correlation between the measured CO2 levels and the measured H2O levels in the atmosphere.

The instrument accuracy of the NVAP-M data has been questioned in the comments. If it can really be shown that systematic errors still dominate the data, then no firm conclusions can be drawn as yet.

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