The IPCC back up reports are released months after the Summary for Policymakers for good propaganda reasons.
After people are told the conclusions in the Summary, they have no opportunity to look up the details to see if the conclusions exaggerate, omit uncertainties, omit assumptions, etc.
It also does not matter what the IPCC said in the 1980s or early 1990s.
It does matter what they say NOW, and natural causes of climate change are not featured in the Summary for Policymakers.
If you want to go far back in time, when the IPCC was almost an honest organization, rather than a leftist propaganda machine ... the IPCC once provided wisdom about climate science that seems completely missing from recent Summaries for Policymakers.
For example:
"14.2.2
Predictability in
a Chaotic System"
The climate system is particularly challenging since it is known that components in the system are inherently chaotic; there are feedbacks that could potentially switch sign, and there are central processes that affect the system in a complicated, non-linear manner.
These complex, chaotic, non-linear dynamics are an inherent aspect of the climate system.
As the IPCC WGI Second Assessment Report (IPCC, 1996) (hereafter SAR) has previously noted, “future unexpected,
large and rapid climate system changes (as have occurred in the past) are, by their nature, difficult to predict.
This implies that future climate changes may also involve ‘surprises’.
In particular, these arise from the non-linear, chaotic nature of the climate system
... Progress can be made by investigating non-linear processes and sub-components of the climatic system.”
These thoughts are expanded upon in this report: “Reducing uncertainty in climate projections also requires a better
understanding of these non-linear processes which give rise to thresholds that are present in the climate system.
Observations, palaeoclimatic data, and models suggest that such thresholds exist and that transitions have occurred in the past.
... Comprehensive climate models in conjunction with sustained observational systems, both in situ and remote,
are the only tool to decide whether the evolving climate system is approaching such thresholds.
Our knowledge about the processes, and feedback mechanisms determining them, must be significantly improved in order to extract early signs of such changes from model simulations and observations.” (See Chapter 7, Section 7.7).
14.2.2.1
Initialization and
flux adjustments
" ... Models, by definition, are reduced descriptions of reality and hence incomplete and with error.
Missing pieces and small errors can pose difficulties when models of sub-systems such as the ocean and the atmosphere
are coupled.
As noted in Chapter 8, Section 8.4.2, at the time of the SAR, most coupled models had difficulty in reproducing a stable climate with current atmospheric concentrations of greenhouse gases, and therefore non-physical “flux adjustment terms” were added."
In plain English -- the climate models are "all fluxed up".