Curry on model tuning

Using lots of tuning, CCSM3 agreed well with observations. Without that tuning, and with a better model, CCSM4 shows warming that is way too strong and ends up 0.5C too warm by 2005.
- Judith Curry

Judith,
you keep saying that, but I haven’t seen any evidence for this claim, here or in your uncertainty papers.
- doskonaleszares

Read the Gent et al. paper, they describe this.
- Judith Curry

Where? Could you please provide a quotation?
- doskonaleszare

The relevant text is on page 4, in section 3
- Judith Curry

I assume you mean the following fragment:
[...]
But in this case I’m afraid you are mistaken. They didn’t tune the CCSM3 to “give the correct 20th century variability”, or to “give a good 20th century simulation”, they didn’t even tune the CCSM3 to “the 20th century observations”, and it makes absolutely no sense to claim that the period 2000-2005 is “untuned”, and this is the reason for the temperature discrepancy.

The NCAR team used 1990s values of forcings and observed climatology as the initial state, but
1) their goal was to tune the model to near-zero TOA imbalance for the UNFORCED control run, which is of course inconsistent with “a good 20th century simulation.”
2) since the proper preindustrial control used in 20CEN runs wasn’t that stable, and kept drifting cold with the TOA imbalence of 0.6 Wm-2 even after centuries of integration, your claim that the CCSM3 “was tuned to the 20th century observations” makes no sense at all.
- doskonaleszare

I did not make a mistake. No one from the NCAR team has objected to what I said.
- Judith Curry

Well, I’m afraid that’s no longer true. I contacted with dr. Gerald Meehl Meehl, and he confirmed that they didn’t “tune the model response to fit 20th century observations, and never have.”
- doskonaleszare

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