Clive Best: Trends in Atmospheric Water Vapour

Posted: February 1, 2016 by tallbloke in Analysis, atmosphere, Dataset, modelling

Reblog from Clive Best’s site.

The basis of IPCC predictions is that any moderate warming caused by increased CO2 levels is enhanced by more evaporation from the oceans. Water vapour is itself a strong greenhouse gas and this increase results in a large “positive feedback” boosting climate sensitivity to a doubling of CO2 as high as 6C.
This is all just  theory however, so it is important to observe whether water vapour in the atmosphere has actually increased or not in response to increasing CO2. The data shown below are from the NASA NVAP [1] project based on radiosonde, TIROS,TOVS & SSM/I satellite based data. This data was kindly brought to my attention by Ken Gregory [2].

Fig 1: total Precipitative water vapour in 3 levels in the atmosphere im mm. The 3 curves are Northern Hemisphere, Southern Hemisphere and the “Global average” – see 2) below.

The data from NVAP shows little change in  water vapour from 1988 until 2001 at all levels in the atmosphere.  If anything a  small decrease in the important upper atmospheric layers  in the detail shown below Fig1b.

Fig 1b: detail of TWP for upper layers in atmosphere.

If we now integrate all layers to get the total water vapour column  we then get figure 2:

Figure 2 total water vapour content global averaged for all levels.

There is no evidence whatsoever in NVAP of any increase in water vapour in the atmosphere during the period 1988 – 2001 during which time CO2 levels increased by ~30 ppm (10%) and temperature anomalies by ~0.3C. The data show some  reduction in water vapour  in the radiative crucial upper layers of the atmosphere. Based on this data water vapour feedback looks to be  small or even negative.

This result is  evidence against significant positive feedback from water vapour to CO2 radiative forcing. Small changes in water vapour can completely offset (or enhance) any change in CO2 radiation flux to space. The evidence does not support any trend increase in water vapour with either surface temperature or CO2.


1. see also

2. Ken Gregory points out that our water vapour values calculated by the Fortran program supplied give slightly higher values than that quoted in the new paper: Weather and Climate Analyses Using Improved Global Water Vapor Observations. The reason for this is currently unknown. However that paper also shows no increase in water vapour from 1988 until 2010.


  1. A C Osborn says:

    Another nail in the CAGW theory.

  2. A C Osborn says:

    But it is like a Vampire, it needs a wooden stake through it’s heart.

  3. USteiner says:

    That first link in the Reference is broken. Any way to fix that?

  4. erl happ says:

    It would be good to see the data for the critical Hadley Cell latitudes of the southern hemisphere where cloud cover has a big influence on the uptake of energy by the oceans.

    In the last graph the peak in 1998 is common to other significant data like surface pressure in the mid and high latitudes of the southern hemisphere and 10 hPa temperature over the Antarctic pole let alone the start of the ‘hiatus’ in the progress of global temperature.

    Unfortunately, rational argument and observation will not suffice. There is no argument, no engagement and no responsibility.

  5. bobfj says:

    And WRT overall CO2 sensitivity according to Kevin Trenberth et al, about 50% of heat loss from the surface is due to evapotranspiration at almost 50%. It would seem that this has a big negative feedback. Unfortunately climate scientists are rather neglectful of this possibility and are all competing over radiative effects.

  6. catweazle666 says:

    I can’t remember when I first posted the analyses of the NVAP data from Humlum, Vonder Haar and Solomon et al as evidence that the CAGW thing was a load of old donkey droppings, it was several years ago now.

    Strange how few climate “scientists” seem to admit the implications.