Maybe I'm not sure what point you're trying to make here re sunspot numbers etc.. It seem like you're saying the IPCC sould be taking into account as yet unknown forcings.
That's exactly what I'm saying. One of the basic mandates of scientific methodology is to control or account for all significant variables. Of course this is easy when the experiments are relatively simple and well understood, but with climatology, some of the known forcings and the associated variables are poorly understood and there is an inherent complexity that quickly multiplies the uncertainties to a point where useful conclusions become difficult to make.
Specifically regarding sunspots, it is known that there is a causal link between their aggregate number at maxima and warming of the Earth's atmosphere. Yet the mechanism for how this works is unknown and the magnitude of this effect is also unknown. It may be significant or it may not be.
For the purposes of attributing the correct amount of the observed warming over the 20th century to human activity - which is likely to be the majority, as the IPCC reports state - we need to know roughly how much or how little warming is attributable to sunspot activity, independent of solar irradiance.
The IPCC correctly considers, in considerable detail, variations in solar irradiance as a forcing and also correctly rejects it as a significant factor in warming during the 20th century. Yet, sunspot activity apparently has an effect on the Earth's climate that is independent from solar irradiance and this can't just be ignored because the mechanism isn't understood. This is the mistake the IPCC is making.
The real problem is there is no way to judge this factor's effect on warming because there simply is no information to go on other than we know it exists in some amount. Perhaps the amount truly is minuscule and can be ignored. Or it might be significant and greatly affects the calculation of climate sensitivity.
From the vantage point of proper scientific methodology, the correct action is to acknowledge the uncertainty with an appropriately sized margin of error. The IPCC apparently construes our lack of knowledge as irrelevance and dismisses the issue.
If, in the future, we discover that the effect is truly minuscule, then we can count our blessings that our current calculations were correct in that regard. But if we find out that there was a natural cause behind a significant portion of the warming that we assumed was entirely caused by human activity then the reputation of many scientists, and of science in general, has been flushed down the toilet, providing the true global warming deniers with the ammunition to say the alarmists were using bogus science all along.
And they'd be justified in saying so. Unfortunately, society would then have reason to assume that the entire global warming issue was a hoax and any plans we may have to mitigate the effect of man-made global warming in the future we can kiss goodbye. This can't be allowed to happen, which is why it's so important to rigorously follow proper methodology and accurately account for all variables, even if such accounting might imply global climate change was a bit less of a crisis than we first thought. Sloppy assumptions which exaggerate, however slightly, the effect we humans are having on the climate will prove to be disastrous for long term credibility. I repeat: this can't be allowed to happen.
My assertion is that the way the data is processed limits the use to which the subsequent graph can be used. The processed information is certainly scientifically valid for many purposes germane to the IPCC report. But one use it's been put to is to support the claim that climate temperatures were relatively stable over the past few thousand years while those temperatures began to vary dramatically during the 20th century. This is an unjustified conclusion because the data that makes up the graph has been processed in such a way that this conclusion is unavoidable. Large variations in temperature have been artificially smoothed out during the time period that the proxy data covers, while they are left intact in the period that uses direct data from the 20th century.
This is important to know because some estimates of the ECS use this exact paleo-climate data and the associated observable trends to calculate the results. Further, the assumption that paleo-climate temperatures varied little compared to the past century is used as partial justification to dismiss the significance of all natural forcings as a factor in the observed warming of the 20th century. [See IPCC AR4, Chapter 9 - Understanding and Attributing Climate Change: 9.1, 9.2, 9.3, 9.6, 9.7, FAQ 9.2]
