Failure of IPCC to properly consider solar influence

From CO2Sceptics.com

As I understand it the solar effect on climate has been discounted by the climate modellers because the variation in total solar irradiance between the peak and the trough of a single eleven year (approximately) solar cycle seems far too small to make any difference to global temperature.

There are a number of problems with their assumption as follows:-

The concept of total solar irradiance is purely a convenient construct. We do not know all the different mechanisms by which the sun can have an influence on global temperature either directly or indirectly. The use of the word "total" is therefore misleading. Even the concept of irradiance is vague and maybe incomplete.

The fact is that in the real observed world over centuries cooler weather has been seen to occur at a similar time to longer less active solar cycles and warmer weather similarly occurs with shorter more active solar cycles. If total solar irradiance does not seem to account for it that is no reason to ignore the phenomenon yet the modellers and the IPCC do so. I assume that the reason they ignore it is because, being unaware of the cause of the observed phenomenon, they have no numbers representing it to feed into the models. Their model output should therefore be qualified by an admission that at least one substantial observable real world phenomenon has been wholly omitted. Unfortunately for them that would render the models useless for policy making purposes.

The IPCC and the modellers do recently seem to have come to accept the influence of the EL NINO/ LA NINA cycle as a warming/cooling process. However they currently regard it as a purely redistributive mechanism rather than one which could actually be part of a driving mechanism. They would be in error if variations in solar energy input to the Earth operated a switch between the predominance over time of either EL NINO or LA NINA.

The variation between peaks and troughs in the solar cycle may be very small but if continued over long periods the effects could soon accumulate. If, say, the difference is only 1% then if a reduction or increase in incoming solar energy continues for many years, perhaps over several solar cycles, then it is the cumulative effect that should be considered and that could well be substantial over a number of decades.

There could also be other unknown mechanisms driven by solar changes that exaggerate the effect of small variations in total solar irradiance. A current possibility being investigated is a suggested link between cosmic ray flux and cloudiness. The flux varies depending on the energy from the sun and may drive cloudiness changes.

It is possible that over the millennia the earth has become a very accurate "thermometer" in terms of its reaction to solar heat or other forms of solar energy input. The entirety of the global heat budget may be very sensitive to solar changes. Over millions of years the earth has arrived at a temperature balanced between incoming solar energy and outgoing radiation of energy to space. The balance could well be much finer than we have so far realised. There are certainly no available figures that describe the sensitivity of the global temperature to variations in solar input and without knowing that level of sensitivity as a first step I fail to see how we can know anything useful about the sensitivity of the Earth to other influences.