Why are we defining ‘dangerous climate change’ with respect to the climate of the 18th century, which was the coldest period in the last millennia, with wicked winters? Why not use a reference point of 2000 or 1970? The IPCC doesn’t provide a convincing explanation for the overall warming between 1750 and 1950; according to climate models, human causes contributed only a very small amount to the global warming to during this period (so presumably this overall warming was caused by natural climate variability). Co-opting the period between 1750 and 1950 into the AGW argument muddies the scientific and the policy waters.
It would make much more sense — from a scientific perspective, from the perspective of adaptation and engineering, and in the public communication of climate change — to refer to warming relative to a more recent reference period. Since the emissions reference periods are between 1990 and 2005, this also adds to the argument of citing a more recent reference period for defining ‘dangerous’.
The argument that human caused warming is already ‘dangerous’ — widely made by politicians, the media and some scientists — flies in the face of scientific evidence reported by the IPCC AR5 and SREX. Extreme weather events were worse earlier in the 20th century, and sea level has been rising for millennia, with recent rates of sea level rise comparable to what was observed in the middle 20th century.
It’s almost as though there’s some sort of political agenda at work.
This is all part of the Democrats’ war on science:
Looking forward to a new U.S. President next year, whether the Democrats or the Republicans are in power, I don’t expect a continuation of the status quo on climate science funding. The Democrats are moving away from science towards policy – who needs to spend all that funding on basic climate science research? Global climate modeling might be ‘saved’ if they think these climate models can support local impact assessments (in spite of widespread acknowledgement that they cannot). If the Republicans are elected, Ted Cruz has stated he will stop all funding support for the IPCC and UNFCCC initiatives. That said, he seems to like data and basic scientific research.
It occurs to me to wonder whether this error in the GISS-E2-R ocean mixing parameterisation, which gave rise to AMOC instability in the Pliocene simulation, might possibly account for the model’s behaviour in LU run 1. It looks to me as if something goes seriously wrong with the AMOC in the middle of the 20th century in that run, with no subsequent recovery evident.
But let’s make wealth-destroying policy based on this!
It’s sad how so many people who (ironically) accuse me of being a “climate denier” or a “science denier” are so profoundly ignorant of how science actually works.
[Bumped]
[Update a while later]
An analysis from Judith Curry and Nic Lewis on the latest climate crap from Mann et al:
As I see it, this paper is a giant exercise in circular reasoning:
Assume that the global surface temperature estimates are accurate; ignore the differences with the satellite atmospheric temperatures
Assume that the CMIP5 multi-model ensemble can be used to accurately portray probabilities
Assume that the CMIP5 models adequately simulate internal variability
Assume that external forcing data is sufficiently certain
Assume that the climate models are correct in explaining essentially 100% of the recent warming from CO2
In order for Mann et al.’s analysis to work, you have to buy each of these 5 assumptions; each of these is questionable to varying degrees.