The newly-released Summary for Policymakers of the IPCC’s Working Group I for the AR5 report reveals a dogged attempt to salvage the IPCC’s credibility amidst mounting evidence that it has gone overboard in its attempts to scare the global public over the last quarter century.
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:
“It is extremely likely that human influence on climate caused more than half of the observed increase in global average surface temperature from 1951-2010.”
Let’s examine that last claim for a minute. For the sake of argument, let’s say that 60% of the surface warming (and increase in ocean heat content, as revealed by supposed warming of hundredths of a degree) is indeed due to increased CO2. What would that say about the sensitivity of the climate system?
One would think that this question would be addressed by the IPCC, since it doesn’t require a full-blown 3D climate model to answer.
But I suspect that they know the answer is: “very low climate sensitivity” (we will reveal more on this issue in a few weeks). Even if humans are responsible for 60% of the ocean heating in the last 60 years, it suggests a level of future warming well below what this report implies will happen.
I say “implies” because the new report is worded in such a way that the IPCC can be technically correct, and still convey a maximum amount of alarm (which has been the IPCC’s modus operandi for the last 20+ years). They still leave the door open to a climate sensitivity below 1 deg. C, since they could claim “we didn’t say we were 100% certain…only 95%”.
And probably the biggest omission of the report continues to be the almost total neglect of natural forcing mechanisms of climate change. The climate system is likely at least a little chaotic, with natural variations due to inherent system nonlinearities and time lags (courtesy of the ocean). As I keep harping on, the observed increase in ocean heat content over the last 60 years (if we can believe hundredths of a degree warming is accurate) equates to a global energy imbalance of only 1 part in 1,000. To believe that Mother Nature is incapable of causing such small imbalances, as the IPCC implicitly believes, is not based upon observations but upon assumptions.
What this means is that, 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, …pick your metaphor.