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Correcting climate models vs measurements

Discussion in 'Environmental Discussion' started by bwilson4web, Aug 3, 2015.

  1. bwilson4web

    bwilson4web BMW i3 and Model 3

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    I don't have the paper, yet, but this news report gives a good summary:
    Climate models are even more accurate than you thought | Dana Nuccitelli | Environment | The Guardian

    [​IMG]


    Thus looking at modeled air temperatures and HadCRUT4 observations isn’t quite an apples-to-apples comparison for the oceans. As it turns out, sea surface temperatures haven’t been warming fast as marine air temperatures, so this comparison introduces a bias that makes the observations look cooler than the model simulations. In reality, the comparisons weren’t quite correct. As lead author Kevin Cowtan told me,

    We have highlighted the fact that the planet does not warm uniformly. Air temperatures warm faster than the oceans, air temperatures over land warm faster than global air temperatures. When you put a number on global warming, that number always depends on what you are measuring. And when you do a comparison, you need to ensure you are comparing the same things.

    The model projections have generally reported global air temperatures. That’s quite helpful, because we generally live in the air rather than the water. The observations, by mixing air and water temperatures, are expected to slightly underestimate the warming of the atmosphere.

    The new study addresses this problem by instead blending the modeled air temperatures over land with the modeled sea surface temperatures to allow for an apples-to-apples comparison. . . .

    There is more in the article about Arctic sea ice and random forcing functions including volcanoes. But knowing the error sources, the models can be tuned to include these external, random functions. Piece of cake.

    Bob Wilson
     
  2. austingreen

    austingreen Senior Member

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    I've had some experience with modeling, and those models leave a lot to be desired. Normally before a model is made you choose a measure, then after you get the data you compare to that meausre. If you are off you should .... change the model based on your understanding of the data.

    That is what needs to be done here.

    I have no idea which measure they were supposed to replicate, but that is what they should do. If it was Hadcrut, then we should not willy nilly change the measure because the models seem to be closer to another one. If hadcrut is the wrogn measure, no problem switch it to BEST, or NCDC, or NASA, but give a reason why the new measure is better. I myself like NCDC and my reason for disliking Hadcrut, is they do not have an open explanation of how the algorythim they used to create the data. BEST goes the furthest, providing both data and algorithm, so with a modeler objects to a measure they can set their new algorithm for the test and justify the open methods for reviewers.

    IPCC V gave 2 possible problems in models. Poorly modeled osculations - ENSO was clearly spelled out, sensitivity possibly too high and the lower bound was lowered from IPCC IV, poorly modeled ocean temperatures. Modelling is important but we should not grade existing models on a curve because we like what they say, or don't like what they say. We should ask for accurate models, and hopefully the next batch will improve.
     
  3. bwilson4web

    bwilson4web BMW i3 and Model 3

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    #3 bwilson4web, Aug 3, 2015
    Last edited: Aug 4, 2015
    austingreen likes this.