Doug I did it for her here September 16, 2014 at 10:04 am
In regard to the 50/50 argument by Judith Curry Pick one:
a) Warming since 1950 is predominantly (more than 50%) caused by humans.b) Warming since 1950 is predominantly caused by natural processes.
When faced with a choice between a) and b), I respond: ‘I can’t choose, since i think the most likely split between natural and anthropogenic causes to recent global warming is about 50-50′. Gavin thinks I’m ‘making things up’, so I promised yet another post on this topic.
The issue here is of the likelihood of human induced CO2 production causing the global warming detected from 1950 to 2014.
The basis of this argument is that CO2 increasing at 1.3 ppm a year [2.07 for last decade] from a base of 312 to now 400 PPM is all human induced and that this should cause a rise in average global temperature of 0.2 degrees a decade.
The attribution of the warming is made from assumptions [G and Curry] from models and the models are all programmed to input 0.2 degrees rise a decade [the rise that "must "occur when CO2 is going up at this rate"]. ” the climate models ‘detect’ AGW by comparing natural forcing simulations with anthropogenically forced simulations.
Gavin writes
The basis of the AR5 calculation is summarised in figure 10.5:
Figure 10.5 IPCC AR5
and herein lie a number of problems
Firstly anthropogenic global warming is really GHG [greenhouse gas] warming as humans are supposed to make all of the excess GHG. This is a lot more than the observed warming over this time as 0.2 degrees a decade for 64 years is 1.28 degrees. Strangely this is 130% of the observed warming that has occured, Guess the models did not predict the pause after all.
Secondly CO2 levels are increasing per decade from 0.75 ppm to 2.07 ppm but the models were set with the lower levels. At the same time as we should be seeing an increase in temperature rise we instead have a pause.
Thirdly anthropogenic global warming [ANT] is still put at greater than 100%, ie 110 %, after taking off the supposed negative aerosol effect [OA], which is so unknown that the error bars are bigger than the guesstimate.This is where Gavin obtains his 110% likely range of Anthropogenic warming that he attributes to the IPCC. This is 1.28 degrees minus largest guesstimate with a straight face for aerosol effect.
Fourthly Natural Variation gets a guernsey with the ridiculously low figure of 0.1 degree over 64 years either way, no guesswork here. Judith’s point that AO and PO oscillations and multidecadal waves which may go in 60 ,80 or 100 year cycles is completely ignored by saying that Natural variation should be ignored over a long time as it reverts to the mean. In the time frame given there is every possibility that natural variation, possibly in the order of 0.2 degrees a decade, Could be happening, but this could mean that the 1990’s rise was not caused by humans at all. In a different context on another matter Gavin himself said “in framing this as a binary choice, it gives implicit (but invalid) support to the idea that each choice is equally likely. That this is invalid reasoning should be obvious by simply replacing 50% with any other value and noting that the half/half argument could be made independent of any data.”
Fifthly, as kindly pointed out by Tom Curtis at Skeptical science to the maths challenged Russ R statement that G = +0.9±0.4°C and OA = -0.25±0.35°C. So, by simple math, ANT = 0.65± 0.75°C. So, the PDF would would be centered around 100% (not 110%) of the observed warming with (5-95%) uncertainty of ± 115%. [see first comment at blog , Judith, Russ R. at 06:27 AM on 16 September, 2014 ] , that would be a giant variability due to the OA uncertainty range if correct