He starts: FIGURES in the final draft of the UN’s fourth five-year report on climate change show that the previous report, in 2001, had overestimated the human influence on the climate since the Industrial Revolution by at least one-third. Also, the UN, in its 2007 report, has more than halved its high-end best estimate of the rise in sea level by 2100 from 3 feet to just 17 inches.
Interesting if true… but is it true? Oddly enough, no. The first he amplifies as the 2001 report showed that our greenhouse-gas emissions since 1750 had caused a “radiative forcing” of 2.43 watts per square metre. Our other effects on climate were shown as broadly self-cancelling. In the current draft, the UN has cut its estimate of our net effect on climate by more than a third, to 1.6 watts per square metre. Note the apples-and-oranges juxtaposition of 2.43 and 1.6. The correct value to compare to 2.43 is 1.66 (CO2) + 0.98 (other GHG) = 2.64. So the GHG forcing is assessed as larger not smaller which is unsurprising as we have another 6 years. *Net* anthro is 1.6 in AR4, but should be compared to… there isn’t quite a comparable value from the TAR SPM. Sulphate is about -0.5 in both; land use about -0.2. In the AR4, most of the rest of the negative comes from aerosol indirect, as -0.7 (range -1.8 -0.3); whereas the TAR only gives a range (-2 to 0), but this is about the same as before. So the negatives are pretty well the same as before (though their certainty is now “low” rather than “very low”), the positives a bit bigger, Moncktons supposed reduction is nonsense.
And after that, the sea level rise? The TAR SPM pic is here. The SLR is 0.88 top-of-range and this is presumably what M is using for 3 feet. But thats all-models all-SRES plus land ice uncertainty (except for the WAIS). The value sans land ice uncertainty (which is what the AR4 uses) is 0.7 in the TAR against 0.59 in the AR4. But hold on, 0.7m is 27″. 17″ is 0.43m. Where has M got that from? Top of the B2 range? Average of the A1F1 range? Why would he choose either of those? Also I’m told, but have not verified, that the TAR range is 95% but the AR4 range is 90% uncertainty. So perhaps its better to look at the mid value for which AR4 sez For each scenario, the midpoint of the range in Table SPM-2 is within 10% of the TAR model average for 2090-2099.
[Update: I'm told that 17" = 43cm *is* from the A1F1 mean, which was in an early draft but later removed. But of course that can't be compared to a top-of-range estimate from the TAR]
Thats M’s first two points disposed of. What else? The UN’s draft Summary for Policymakers contains no apology for the defective and discredited “hockey-stick” graph… Indeed no, to the contrary, it reaffirms it: “Average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years and likely the highest in at least the past 1300 years.”
Even less sanely: Globally, temperature is not rising at all, and sea level is not rising anything like as fast as had been forecast. The temperature bit just relies on cherry-picking a start point of 1998 and is just silly. The sea level assertion is incomprehensible: current SLR is 3 mm/yr from satellite; the mid-range value for 2100 from the TAR was 0.4m which is 4 mm/yr. But since the graph is convex the “prediction” was clearly for about 3 mm/yr which was spot on.
You should also, of course, read the RC post.
[Forgot to include: The UN's best estimate of projected temperature increase in response to CO2 reaching 560 parts per million, twice the level in 1750, was 3.5C in the 2001 report. Now it is down to 3C. Is not clear what he means by this so you have to guess. AR4 doesn't give a single value. But the A1B best-estimate is 2.8 which is the closest number to 3 in the table. In the TAR it was... 2.9 reading of fig 5. Where M gets 3.5 from I don't know. Oh hold on... what does he mean "560 ppmv"? Thats not A1B at 2100. Is he confusing climate sensitivity with warming-at-date?]
[Update: sadly those clever chaps at the WSJ have been taken in by Moncktons nonsense :-(. I suppose its too much to ask for them to understand any of this well enough to even look up the numbers... -W]