IPCC really doesn't know Clouds at all.

Bows and flows of angel hair
And ice cream castles in the air
And feather canyons everywhere
I've looked at clouds that way

But now they only block the sun
They rain and snow on everyone
So many things I would have done
But clouds got in my way

Joni Mitchell admitted that she really didn't know clouds at all and now, a new peer-reviewed paper shows that the IPCC's Climate models don't know clouds either.
    Published in Geophysical Research Letters Vol 39 Issue 21:

    The ‘too few, too bright’ tropical low-cloud problem in CMIP5 models (link)

    1. C. Nam,
    2. S. Bony, 
    3. J.L.Dufresne,
    4. H.Chepfer
    Previous generations of climate models have been shown to under-estimate 
    the occurrence of tropical low-level clouds and to over-estimate their 
    radiative effects. This study analyzes outputs from multiple climate models 
    participating in the Fifth phase of the Coupled Model Intercomparison 
    Project (CMIP5) using the Cloud Feedback Model Intercomparison Project 
    Observations Simulator Package (COSP), and compares them with different 
    satellite data sets. Those include CALIPSO lidar observations, PARASOL 
    mono-directional reflectances and CERES radiative fluxes at the top of the 
    atmosphere. We show that current state-of-the-art climate models predict 
    overly bright low-clouds, even for a correct low-cloud cover. The impact of 
    these biases on the Earth' radiation budget, however, is reduced by 
    compensating errors. Those include the tendency of models to under-
    estimate the low-cloud cover and to over-estimate the occurrence of mid- and 
    high-clouds above low-clouds. Finally, we show that models poorly represent 
    the dependence of the vertical structure of low-clouds on large-scale 
    environmental conditions. The implications of this ‘too few, too bright 
    low-cloud problem’ for climate sensitivity and model development are 

              I've looked at clouds from both sides now,
                  From up and down, and still somehow

              It's cloud illusions i recall.

                  I really don't know clouds at all. (Joni Mitchell)

The authors write that the response of low-level clouds has long been identified as "a key source of
uncertainty for model cloud feedbacks under climate change," citing the work of Bony and Dufresne
 (2005), Webb et al. (2006), Wyant et al. (2006) and Medeiros et al. (2008). And they state that "the
ability of climate models to simulate low-clouds and their radiative properties" plays a huge role in
assessing "our confidence in climate projections."

What was done
In studying this unresolved dilemma, Nam et al. analyzed "outputs from multiple climate models
participating in the Fifth phase of the Coupled Model Intercomparison Project (CMIP5) using the
Cloud Feedback Model Intercomparison Project Observations Simulator Package (COSP), and
compared them with different satellite data sets," including "CALIPSO lidar observations, PARASOL
mono-directional reflectances, and CERES radiative fluxes at the top of the atmosphere."

What was learned
In the words of the four French researchers, "the current generation of climate models still
experiences difficulties in predicting the low-cloud cover and its radiative effects." In particular,
they report that the models: (1) "under-estimate low-cloud cover in the tropics," (2) "over-estimate
optical thickness of low-clouds, particularly in shallow cumulus regimes," (3) "poorly represent the
dependence of the low-cloud vertical structure on large-scale environmental conditions," and (4)
"predict stratocumulus-type of clouds in regimes where shallow cumulus cloud-types should
prevail." However, they say that "the impact of these biases on the Earth's radiation budget ... is
reduced by compensating errors [italics added]," including "the tendency of models to under-
estimate the low-cloud cover and to over-estimate the occurrence of mid- and high-clouds above

What it means
Well isn't that just dandy! We have the leaders of numerous nations forging ahead with energy
policy prescriptions for halting global warming - which has been non-existent for close to two
decades now - based on climate change projections derived from mathematical models harboring
acknowledged problems that are supposedly overcome by compensating errors. If these people
were building bridges, would you want to drive across one of them???

Read More at CO2 Science.