by Bob Irvine

A knowledge of Greenhouse gases is fundamental to any understanding of global surface temperatures. The presence of GHGs in our atmosphere has increased the global surface temperature by about 33C.

There are multiple lines of evidence, however, that challenge the strong water vapour feedback to a small initial CO2 forcing.  These strong positive feedbacks are central to the IPCC narrative.

These lines of evidence include.

  • The failure of all models and catastrophic warming projections.
  • The stubborn refusal of atmospheric Precipitable Water Vapour (PWV) concentration to rise in recent years.
  • The strength of convection cells in the tropics that have kept tropical temperatures approximately the same for many millions of years.
  • Irrigation and extra humidity generally coincide with cooler temperatures.
  • The hot spot as a signature of the positive Water Vapour (WV) feedback and its opposite, the negative lapse rate feedback, has not occurred.


The IPCC and most sceptics believe that a doubling of CO2 in the atmosphere will produce about 1.04 ± 0.1C (Andrews 2012, CMIP5) warming at equilibrium if we assume that there are no feedbacks in the system. This is not controversial.

The IPCC then multiplies this by three to get an after feedback warming of 3.0 ± 1.5C largely due to the amplifying effect of extra water vapour and cloud changes. This has been their position for 40 odd years now. It is political death to change your mind, apparently. Positive feedbacks of this size would be destabilizing, utterly improbable, and are likely the result of political interference in the scientific process.

These exaggerated feedbacks have caused all the IPCCs projections to fail within 10 years of their announcement. The first of these was James Hansen in 1988.

To understand why these models have failed we need to understand the workings of the atmosphere and the way increasing CO2 increases temperature. We also need to understand the important role water vapour and convection play in this process.


Increasing CO2 warms the atmosphere in two ways.

These are the “surface” and “atmosphere” effect. These two mechanisms combine to give a total effect as depicted in Figure 1.

  1. The Surface or Radiative Effect.

There is a transparent window to space at wavelengths approximately between 9 to 16 microns. Long wave radiation in this wavelength range generally passes unrestricted to space through this window. The introduction of CO2 to the atmosphere restricts radiative flow centred around 15 microns. It closes this window slightly. This warms the planet, as shown in Figure 1 but loses all potency by the time CO2 concentrations reach about 600 ppm.

2. The Atmosphere Effect

The atmosphere effect involves the balancing of two factors. Higher CO2 concentrations mean a higher average CO2 emission height.

  • A Higher average emission height means lower gas concentrations at this emission height. This implies a longer free path for energy photons with a consequent cooling of the planet as more of these photons make it out to space.
  •  A higher emission height also means lower individual emissions due to lower temperatures at the average emission height. This implies an opposite tendency to warm the planet.

Figure 1. The two ways (Radiative and Atmosphere) CO2 increase causes warming and their total effect. The “Y” access is “outgoing radiation”, so a decreasing line indicates warming of the planet. Acknowledgement to Clive Best for this graphic.

The Atmosphere Effect

At lower CO2 concentrations changes in individual emissions due to temperature do not play as big a part as changes in free path length. At these lower concentrations, temperatures actually fall due to the atmosphere effect as CO2 concentrations increase.

By calculating the radiation to space from each level, these two conflicting forces can be combined to give an effective emission height for varying CO2 concentrations. See Figure 2.

The net result is shown as the “Atmosphere” curve in Figure 1. Emission to space via the “Atmosphere” effect alone increases as CO2 concentrations increase from zero to 300 ppm cooling the atmosphere. At concentrations higher than 300 ppm emission to space falls warming the planet.

Clive Best observes (Ref. 1) that this 300 ppm just happens to be the historical pre-industrial CO2 concentration. Can this possibly be a coincidence?

Figure 2. Varying emission heights for different CO2 concentrations. Notice greater emissions to space due to the “Atmosphere” effect at 280 ppm than at 200 ppm. The “Atmosphere” effect cooled the planet as CO2 concentrations rose from 200 to 280 ppm. Acknowledgement to Clive Best for this graphic.


GHGs are produced by two dominant mechanisms. Solar heating of the oceans (WV) and the Carbon cycle (CO2).

The sun delivers 340 W/Mto the earths system. This is reduced to 240 W/Mafter the earth’s albedo or reflectivity is considered. This 240 W/Mmust eventually be reradiated back to space either at the surface or at some level of the atmosphere. The earth system needs to be in balance.

If the atmosphere had no GHGs or there was no atmosphere, then the earth would reradiate this 240 W/Mat or near the surface. By calculation, the surface would be, in this case about minus 18C.

As GHG concentrations increase, the passage of this radiation to space is restricted. This warms the surface which increases emissions at the surface. A hotter surface emits more radiation. No system can emit more than it receives so the average emission height must rise in the atmosphere to the point where the 240 W/Mis again radiated to space. The earth system must remain in balance.

This process has developed on the earth to the current settings. The surface is now at plus 15C and radiating at about 390 W/M. The atmosphere cools as we rise to the point where it averages minus 18C and radiates 240 W/Mto space. The earth system is in balance again. This height is known as the emission height and averages about 5 km at the present time (higher in the tropics and lower at the poles).

The Greenhouse gases are therefore responsible for the 33C (15C minus -18C) warming seen at the earth’s surface. This greenhouse effect is currently made up of approximately 20% CO2 and other minor GHGs and 80% Water Vapour (WV) and cloud. The 80% GHG contribution of WV and cloud is almost totally caused by the sun’s 240W/M2. The 3.7W/Madded by a doubling of CO2 makes very little difference to the atmosphere’s WV and cloud content, for obvious reasons.

CO2 also has an efficacy problem when it comes to ocean warming. Water is opaque to the wavelengths reemitted by CO2 while solar energy is absorbed efficiently. It is quite possible that this further reduces the CO2 effect on WV, although this is difficult to quantify as energy from CO2 is returned immediately to the atmosphere as both radiation and latent heat.

See Ref. 2 for a summary of the various estimates of WV feedback.

It is no surprise then that no rise in atmospheric WV content has been detected in recent years despite CO2 concentrations moving from 280 ppm to 410 ppm due largely to human activity. see also

Figure 3. Global Precipitable Water Vapour. NASA.

New paper on Global Water Vapor puts climate modelers in a bind – Watts Up With That?

 “Weather And Climate Analyses Using Improved Global Water Vapor Observations” By Vonder Haar Et Al 2012

Figure 4. Global Precipitable Water Vapour. Vonder Haar et al, 2012.

Figure 5. ECMWF(red) and NCEP(blue) Precipitable Water Vapour (PWV) time series averaged over (a) global, (b) tropical, (c) temperate, and (d) polar regions during the period 1979–2014. These are modelled PWV series. (Chen, Lui 2016)

From the paper’s abstract;

“The variability and trend in global precipitable water vapor (PWV) from 1979 to 2014 are analysed using the PWV data sets from the ERA‐Interim reanalysis of the European Centre for Medium‐Range Weather Forecasts (ECMWF), reanalysis of the National Centres for Environmental Prediction (NCEP), radiosonde, Global Positioning System (GPS), and microwave satellite observations. 

PWV data from the ECMWF and NCEP have been evaluated by radiosonde, GPS, and microwave satellite observations, showing that ECMWF has higher accuracy than NCEP. Over the oceans, ECMWF has a much better agreement with the microwave satellite than NCEP. 

An upward trend in the global PWV is evident in all the five PWV data sets over three study periods: 1979–2014, 1992–2014, and 2000–2014.     ……..

It is found that ECMWF overestimates the PWV over the ocean prior to 1992. Thus, two more periods, 1992–2014 and 2000–2014, are studied. Increasing PWV trends are observed from all the five data sets in the two periods: 1992–2014 and 2000–2014.”

In other words, the red model in Figure 5 is more accurate and shows close to zero increase in PWV from 1979 to 2014.

I cannot let this pass. Climate science truly is amazing. The hat-tipping to the dominant warming narrative not only knows no bounds it also knows no subtlety. The last two periods mentioned start at the low point of the Mt Pinatubo eruption (1992) and the low point of the strong La Nina in 2000. The only reason they show an increasing upward trend is because they start at the lowest possible points and are run over shorter and shorter periods. Extraordinary!

Also, if ECMWF overestimates the period 1979 to 1992 then so does NCEP as they both have similar rates of declining PWV (0.5mm) as measured using the authors methods.

It should be remembered that both these series, ECMWF and NCEP, are models and subject to the usual biases. The cherry picking of the two later period start dates is, therefore, not a good look. The figures the authors use to justify their conclusion are in the paper linked. They are taken from single year to single year and not smoothed in any way.

These, however, are annoying side issues. PWV has not increased in any significant way since 1979 according to the ECMWF. Without the Mt Chichon eruption in 1982 it is likely that, according to the more accurate ECMWF model, PWV would have fallen over the period 1979 to 2014.


We have already seen how the main positive feedback (WV and clouds) claimed by the IPCC does not appear to be happening as expected. Now let’s look at the three main negative feedbacks.

  1. Plank Feedback.

A body radiates according to the 4th power of the temperature of that body implying that a large proportion of any warming due to CO2 is quickly returned to space. The initial 1.04C warming from a doubling of CO2 is reduced significantly in this way.

  • Convection.

Higher temperature drives increased convection. The Earth hosts 1000 or more powerful tropical storms at any one time. These storms are driven by water vapour content and temperature. They transfer an enormous amount of energy from the surface to space. Without this transfer of energy, the surface would be significantly hotter.  

Convection in the atmosphere is extremely complex. If the allowances made by the IPCC for convection are only slightly out, their sensitivity estimates will be miles out. This alone could explain the failure of the climate models that are based on these estimates.

The strength of convection in the moist tropics has an enormous stabilising effect as seen in Figure 6 below.

Credits: Christopher R. Scotese. Palemap Project 2015

Figure 6. Convection has kept the tropics approximately the same temperature for many millions of years. There is no significant change in tropical temperatures from a severe icehouse earth to an extreme hothouse earth.

  • The Lapse rate feedback.

A direct result of surface warming from increased CO2 is increased atmospheric moisture content at the surface. This reduces the lapse rate toward the moist adiabat. A reduced lapse rate must mean that condensation and average emission to space occur at a higher altitude.

Condensation at a higher altitude must mean warming of the upper atmosphere, particularly above the tropics. This is known colloquially as the “hot spot”. It is a direct consequence of increased water vapour and is a significant negative feedback for the following reasons.

As CO2 increases it emits from a higher cooler altitude and consequently emits less energy to space, warming the planet (See the “Atmosphere” effect in Figure 1.). The hot spot discussed above increases the temperature at this higher CO2 emission height, thereby reducing the warming effect of CO2. It is for this reason a negative feedback.

This predicted hot spot high above the tropics does not appear to be happening. The most likely explanation for this is that surface warming increases convection to the point where it overwhelms most of the warming from CO2.

The IPCC attempted to hide this lack of a hot spot in the AR5. It is after all critical to their exaggerated positive feedbacks. Professor Christy explains in the quote below.

          “Unfortunately, it was buried in the Supplementary Material of Chapter 10 without comment.  In Fig. 4, I present the figure that appeared in this IPCC section.  I was a reviewer (a relatively minor position in that report) in the AR5 and had insisted that such a figure be shown in the main text because of its profound importance, but the government appointed lead authors decided against it.  They opted to place it in the Supplementary Material where little attention would be paid, and to fashion the chart in such a way as to make it difficult to understand and interpret.”

For the period 1979 to 2016. Compare NASA GISS Model (Top Left) to satellite bulk atmosphere observations from UAH (Bottom Left), RSS (Bottom Right) and the Universal RAwinsonde Observation Program (RAOB) (Balloon Data) (Top Right). The observations clearly indicate the lack of the predicted hot spot.

Figure 7. The lack of a hot spot as actually measured compared to modelled.


These exaggerated positive feedbacks have caused all the IPCCs forecasts to fail within 10 years of their announcement. These forecasts have consistently failed since the first one was attempted by James Hansen in 1988. See Figure 8 below. The most recent of these is the predicted temperature increase in the Fourth Assessment Report 2007. See Figure 9 below.

Figure 8. Hansen’s failed predictions from 1988. CO2 concentrations have actually grown faster than scenario “A”. The black and red lines are the heavily adjusted surface record (Always adding extra warming on average).

Current CO2 concentrations are increasing at a rate similar to the A1T and B2 scenarios in the 4AR IPCC report copied here. I have used them for this reason.

These scenarios result in between 750ppm and 800 ppm CO2 concentration in the year 2100. Read the above link to get a sense of the IPCCs processes and their position on future warming.

Figure 9, The IPCC forecast from 2007 compared to actual temperatures. The red line is the Hadcrut4 temperature series.  It is similar to the NASA GISS series and has been adjusted many times. The blue line is the more accurate Mid Troposphere Satellite Temperature data. The yellow line is the NAS data from 1975. NAS was the precursor of NASA and was considered state of the art in 1975.  The 2007 model predictions (Grey Line) are already 0.7C warmer than the measured data in 2021.

 Five-year averaged values of annual mean (1979-2015) global bulk (termed “midtropospheric” or “MT”) temperature as depicted by the average of 102 IPCC CMIP5 climate models (red), the average of 3 satellite datasets (green – UAH, RSS, NOAA) and 4 balloon datasets (blue, NOAA, UKMet, RICH, RAOBCORE).

Figure 10. The graph presented to the US House Committee on Science, Space and Technology by John Christy in 2016.  According to the GHG theory, Mid-Tropospheric temperature rise is the fingerprint of GHG warming. It is obvious that the models with their high feedbacks produce more warming in this area than do our most accurate temperature measure, the satellites.  The balloon data also agrees well with the satellites and is well below the models.

Reference 1;  Effective Emission Height | Clive Best

Reference 2; climate feedbacks

via Watts Up With That?

May 16, 2021