Climate models

Discussion in 'Environmental Discussion' started by bwilson4web, Dec 7, 2019.

  1. bwilson4web

    bwilson4web i3 and Prime

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    Source: Even 50 Years Ago, Climate Models Were Way More Accurate Than Deniers Claim

    The study, published Wednesday in Geophysical Research Letters, finds that most of the models examined were uncannily accurate in projecting how much the world would warm in response to increasing amounts of planet-warming greenhouse gases. Such gases, chiefly the main long-lived greenhouse gas pollutant, carbon dioxide, hit record highs this year, according to a new UN report out Tuesday.

    They are now higher than at any other time in human history.

    The study does fault some of the models, including one of the most famous calculations by former NASA researcher James Hansen, for overestimating warming because they assumed there would be even greater amounts of greenhouse gases in the atmosphere than what actually occurred. These assumptions mostly involved non-CO2 greenhouse gases, such as methane.

    Hansen's projection, says study lead author Zeke Hausfather, a researcher at the University of California at Berkeley, erred by about 50 percent because it did not foresee a significant drop in emissions of substances that deplete the stratospheric ozone layer.


    Many of those gases are also powerful global warming agents. Hansen also didn't foresee a temporary stabilization in methane emissions during the 2000s, Hausfather says.

    However, his model, like many of the others examined in the new study, got it right on the basic relationship between greenhouse gas emissions and the amount of warming they would cause. The errors came from poorly predicting bigger wild cards: How societal factors would govern future emissions through economic growth, emissions reduction agreements, and other factors.

    Bob Wilson
     
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  2. fuzzy1

    fuzzy1 Senior Member

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    See also: Climate Models Got It Right on Global Warming

    "But the issue with Hansen’s model wasn’t its physics, Hausfather and colleagues point out. The model assumed higher emissions of methane and chlorofluorocarbons, both potent greenhouse gases, than actually occurred. That’s in part because the model did not account for the future impact of the Montreal Protocol, an international agreement to phase out the use of chlorofluorocarbons in an effort to reverse the ozone hole.


    “If you went back and reran that model with the actual levels of CO2 in the atmosphere and methane and chlorofluorocarbons, you would have gotten a value that was indistinguishable from the warming that we’ve actually observed,” Hausfather said."
     
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  3. tochatihu

    tochatihu Senior Member

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    I am downloading this article now.

    Hausfather quote @2 seems like a reasonable thing to attempt. But that Hansen model is pretty old news in the current broader scheme of things.

    Hausfather et al. ran this suite of models without solar and volcanic forcing and justified that decision. But there again is an opportunity for redoing. I wonder how sensitive these models would be over a range of solar flux variations that might occur in coming decades.

    All the science media websites I've seen describe this as ending in 2007, which made me wonder why not continue? The article shows they actually did, for some models, through 2017.

    Figure 2 shows range of observed +T in degrees C per decade. All the midpoints were from 0.16 to 0.2, which is what we were all thinking (right?).

    I asked grad students to combine such +T with knowledge of tropospheric lapse rates vs. elevation (~6 oC per 1000 m). How fast are climates moving uphill? They did not understand how to begin, so Dec 18 I will present a workshop on 'dimensional analysis'.
     
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