An *Inconsistent With* Spotted, and Defended

May 21st, 2008

Posted by: Roger Pielke, Jr.

Readers following recent threads know that I’ve been looking for instances where scientists make claims that some observations are “inconsistent with” the results from climate models. The reason for such a search is that it is all too easy for modelers to claim that anything and everything under the sun is “consistent with” their predictions, sometimes to avoid the perception of a loss of credibility in the political battle over climate change.

I am happy to report that claims of “inconsistent with” do exist. Here is an example from a paper just out by Knutson et al. in Nature Geoscience:

Our results using the ensemble-mean global model projections (Fig. 4) are inconsistent with the notion of large, upward trends in tropical storm and hurricane frequency over the twentieth century, driven by greenhouse warming.

The climate modelers at Real Climate apparently don’t like the phrase “inconsistent with” in the context of models and try to air brush it away when they write of Knutson et al.:

. . .we know that (i) the warming [of the oceans] is likely in large part anthropogenic, and (ii) that the recent increases in TC frequency are related to that warming. It hardly seems a leap of faith to put two-and-two together and conclude that there is likely a relationship between anthropogenic warming and increased Atlantic TC activity.

Knutson et al. respond in the comments that this in fact is not how to interpret their paper, and — kudos to them — take strong, public issue with the weaselly words implying a connection that they don’t show (emphasis added in the below, and I’ve copied the whole comment for the entire context):

Mike [Mann],

Statement (i), that “the warming [of the tropical Atlantic Ocean] is likely in large part anthropogenic.” is reasonable, taking “anthropogenic” to mean “greenhouse gas”, given the work of Santer et al (2006, PNAS), Knutson et al (2006, J. Clim.), and Gillett et al (2008, G.R.L.). To quote from Gillett et al:

…our results indicate that greenhouse gas increases are indeed likely the dominant cause of [tropical Atlantic] warming…

However, statement (ii), that “the recent increases in [Atlantic] TC (tropical cyclone) frequency are related to that warming” is vague – with “related to” allowing an interpretation that includes anything from a negative relationship, to a minor contribution, to local SST warming being the dominant dynamical control on TC frequency increase. Some might interpret “related to” to mean “are dominantly controlled by”, and we think the evidence does not justify such a strong statement. In particular, the results of Knutson et al (2008) do not support such an attribution statement,if one focuses on the greenhouse gas part of the anthropogenic signal. Quoting from page 5 of the paper:

Our results using the ensemble-mean global model projections (Fig. 4) are inconsistent [emphasis added] with the notion of large, upward trends in tropical storm and hurricane frequency over the twentieth century, driven by greenhouse warming

We agree that TC activity and local Atlantic SSTs are correlated but do not view this correlation as implying causation. The alternative, consistent with our results, is that there is a causal nonlocal relationship between Atlantic TC activity and the tropical SST field. The simplest version uses the difference between Atlantic and Tropical-mean SST changes as the predictor (Swanson 2008, Non-locality of Atlantic tropical cyclone intensities, G-cubed, 9, Q04V01). This picture is also consistent with non-local control on wind shear (e.g. Latif et al 2007, G.RL.), atmospheric stability (e.g., Shen et al 2000, J. Clim.) and maximum potential intensity (e.g., Vecchi and Soden, 2007, Nature).

We view the SST change in the tropical Atlantic relative to the rest of the tropics as the key to these questions. Warming in recent decades has been particularly prominent in the northern tropical Atlantic, but such a pattern is not evident in the consensus of simulations of the response to increasing greenhouse gases. So, whether changes in Atlantic SST relative to the rest of the tropics – that according to our hypothesis have resulted in the changes in hurricane activity – were primarily caused by changes in radiative forcing, or whether they were primarily caused by internal climate variability, or (most likely) whether both were involved, is obviously an important issue, but this is not addressed by our paper

Now a word of caution — Knutson et al. 2008 is by no means the last word on hurricanes and global warming, and the issue remains highly contested, and will remain so for a long time. Of course, you heard that (accurate) assessment of the state of this particular area of climate science here a long time ago (PDF ;-)

Knutson et al. is notable because it clearly identifies observations “inconsistent with” what the models report which should give us greater confidence in research focused on generating climate predictions. We should have greater confidence because if practically everything observed is claimed to be “consistent with” model predictions, then climate models are pretty useless tools for decision making.

8 Responses to “An *Inconsistent With* Spotted, and Defended”

  1. lucia Says:

    In my opinion, admission that some results are inconsistent with models also gives us more confidence in the modelers themselves. The process of improving models requires modelers to identify inconsistencies with data and subsequently, to focus on the improvements required to create more skillful models.

    If inconsistencies exist, but are either not noticed or are denied, then appropriate steps to improve models will likely not be undertaken. In most fields, modelers take even apparent inconsistencies between the central tendencies of their predictions and the phenomena they wish to observe quite seriously.

    Hopefully, climate modelers are able to identify and admit inconsistencies in private, even if they wish to prevent others from discussing them in public.

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  3. Douglas Hoyt Says:

    According to Lozier et al (, the spatial warming of the North Atlantic provides no confirmation that it is due to greenhouse gases.

    The abstract reads

    “The total heat gained by the North Atlantic Ocean over the past 50 years is equivalent to a basinwide increase in the flux of heat across the ocean surface of 0.4 ± 0.05 watts per square meter. We show, however, that this basin has not warmed uniformly: Although the tropics and subtropics have warmed, the subpolar ocean has cooled. These regional differences require local surface heat flux changes (±4 watts per square meter) much larger than the basinwide average. Model investigations show that these regional differences can be explained by large-scale, decadal variability in wind and buoyancy forcing as measured by the North Atlantic Oscillation index. Whether the overall heat gain is due to anthropogenic warming is difficult to confirm because strong natural variability in this ocean basin is potentially masking such input at the present time.”

    “Inconsistent with AGW” might be an appropriate phrase to describe this paper and confirms some of the quotes from Knutson that you give.

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  5. Roger Pielke, Jr. Says:

    Douglas- Thanks for the link, seems like a nice site ;-)

    I do want to emphasize that there is an important distinction between being “inconsistent with” predictions and “inconsistent with” AGW as you write.

    Nothing in my comments should be taken as being “inconsistent with” AGW . . .

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  7. Len Ornstein Says:


    Could you please clarify your statements in response to Douglas?

    By “‘inconsistent with’ AGW” do you mean inconsistent with ‘reasonable’ projections of average global temperature OBSERVATIONS?

    By “‘inconsistent with’ predictions” do you mean inconsistent GCM projections?

    Both seem to be predictions, subject to uncertainty.

    Len Ornstein

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  9. Roger Pielke, Jr. Says:


    Sure, if by AGW Douglas means that the increase in greenhouse gases emitted by humans has effects of the climate system, and among these effects include a long-term warming of the globe, then nothing I’ve posted is inconsistent with this perspective of AGW.

    Now given that, there are a lot of things that might be observed which are inconsistent with the specific predictions of climate models on the short (and long-term). We’ve discussed the short term frequently here. But I don’t put much faith into, for instance, predictions for crop yields in Zimbabwe in 2085.

    My interest here has continued to be in predictions, and especially their usefulness in decision making, given AGW (as Douglas puts it).

    Hope this clarifies.

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  11. Boris Says:

    For once, can you have a post that mentions RC without the childish jabs? You’re beginning to sound like Steve McIntyre over here, maybe not up to his “vicious little men” level, but stil…

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  13. Roger Pielke, Jr. Says:

    Boris- Thanks for your comment on tone, noted and I’ll try to keep it above board.

    I see that RC has a post today that begins “when global warming inactivists need to trot out somebody with some semblance of scientific credentials . . .”

    I hope you’ll express your concerns about tone there as well . . . Thanks!

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  15. Lupo Says:

    Boris suggest RC do that? Or RC change their tone? Roger, you need a vacation!