Home > AGW, Data, Omniclimate, Science, Skepticism > Climate Models: How Much Difference is Too Much Difference?

Climate Models: How Much Difference is Too Much Difference?

Does anyboy know the answer?

I re-post here a comment I just left at RealClimate (one never knows what gets published over there, and what doesn’t…)

Re: #101 As a matter of fact if you search on PubMed http://www.ncbi.nlm.nih.gov/pubmed/ there are four articles with my name. In two of them I appear as first author. And no, they are not first-rated earth-shattering Science or Nature articles about climate science.

But as we all agree now, that’s beside the point.

Let’s me start again from a simple question. Hansen et al did compare model results to observations.

“Climate simulations for 1880–2003 with GISS modelE”, Clim Dyn (2007) 29:661–696 – DOI 10.1007/s00382-007-0255-8

For example, consider fig. 9 (the PDF of the article is on the internet, apologies but I do not have time to search for it right now):

“Fig. 9 Global maps of temperature change in observations (top row) and in the model runs of Fig. 8, for 1880–2003 and several subperiods. […]”

Observations there are shown in periods respectively of 124 years (1880-2003), 54 years, 61 years, 40 years and finally 25 years (1979-2003).

Presumably, this provides a first approximation of what time spans are needed to talk about climate (around 25 years). The actual shortest period may be 40 years or longer, as 1979-2003 has been chosen primarily as “the era of extensive satellite observations”. Please correct me if am wrong.

Let’s take now a clear-cut example. The authors write “All forcings together yield a global mean warming ~0.1C less than observed for the full period 1880–2003.”. And that’s a remarkable result.

But…may I ask this rather elementary question: say, if the global mean warming yielded by all forcings together had been much less, or much more than observed, what would have been the (absolute) threshold above which the climate simulations would have been declared a failure?

Or has this question no meaning either? If not, why not?

Once again, I am consciously simplifying things here but this is a blog…more a brainstorming session than a week-long workshop.

  1. 2008/05/11 at 20:36

    A very disturbing thing about the IPCC approach is the willfull negligence of validation. Picking on aspect after fact and proclaim model skill in its prognosis is so wrong on so many accounts that I cannot possibly see a scientist making such a claim without being disingenuous.

    The issue Realclimate should answer is not if models may be correct, but wether someone have SHOWN them to have any skill. As the IPCC have neglected validation my assumption is that models have no skill at all.

  2. 2008/05/07 at 22:52

    Oh, sorry. I posted this in the wrong forum! I’ll better try at RC again. 😉

  3. 2008/05/07 at 22:51

    Ray Ladbury #104: “what is already known (e.g. CO2 sensitivity)”

    I think this is a false prerequisite, and those isn’t good in any science.

    You clain that something is already known. The direct temperature sensitivity is for 560 ppm about 1 degrees C, but the climate models gives CO2 a major importance of climate fluctuations, and also it assumes positive feedback which at least shall double the direct warming effect.

    For sure we don’t know if we have positive feedback. The climate may very well be dominating by negative feedbacks (many physicists and/or people with good knowledge in system control thinks so). We also don’t know from empirical science that CO2 is a dominating force in climate change.

    Quite likely CO2 isn’t dominating force. The climate model engineers have a fixed view on this so that they can achieve climate models, but actually they know very little about e.g. the impact of clouds in natural climate change. Due to Penn State Paleoclimatologists Lee Kump and David Pollard says that CO2 didn’t caused the warmth during the Cretaceous and Eocene periods. Instead they have found that the sun’s warming effect increased 6-10 percent due to fewer low lwvwl clouds. (Surprice… May Svensmark be right in the end?)


    Also rmember that NASA’s satellite Aqua recently found that a warmer atmosphere contains less water, so the most important positive feedback in the climate models is actually no more! This is of course damaging to CO2 sensitivity prediction in the AGW science (which I regard as bad science). The impact directly from additional CO2 in the atmosphere shall at this point be at most some 10th of a degree Celsius. It may very well be less.

  4. 2008/05/07 at 20:24


    I just gave a comment on realClimate too. (I hope they don’t erase it. I have the same experience, often when Realclimate and the guys there are criticized in my reply to any reader.)

    I just wanted to mention something “sligthly” (or a lot!) offtopic in my comment, about a study which explains warm periods millions of years ago with lack of clouds. I guess Svensmark and Shaviv would like it!

    Brett Anderson about the study it here:

    An article here:

    Maybe you already knew it well..!

  1. 2008/05/02 at 23:47

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