Spencer: 'The recent ~15 year lull in warming is hardly mentioned at all (nothing to see here, move along). A best estimate for climate sensitivity — unarguably THE most important climate change variable — is no longer provided, due to mounting contradictory evidence on whether the climate system really cares very much about whether there are 2, or 3, or 4, parts of CO2 per 10,000 parts atmosphere. YET…the IPCC claims their confidence has DOUBLED (uncertainty reduced from 10% that 5%) regarding their claim that humans are most of the cause behind the warming trend in the last 50 years or so.'
'Without knowing just how much of recent warming is natural, there is no way to know how much is anthropogenic *nor* how sensitive the climate system is. This is a glaring source of uncertainty that the IPCC continues to gloss over, sweep under the rug'