Friday, February 14, 2020

Judith Curry's temperature predictions - charted

Sou | 7:27 AM Go to the first of 20 comments. Add a comment
It's been brought to my attention that there's another set of projections guesses about global surface temperature floating about, this time from Judith Curry.

I don't have time to go into her "arguments" in detail. Suffice to say she seems to be hanging on to the failed "stadium wave" theory and has maybe tossed in a few other ideas as well such as the Atlantic Multidecadal Oscillation flavoured with a smidgen of "it's the sun".

Judith has put up three options for the temperature change over the next 30 years: warmest +0.7C, moderate +0.11C and coldest -0.5C.

What I will do is what she hasn't (for reasons that seem obvious to me). I'll put up some charts showing her guesses. I can't tell from her post what she's used as a baseline, so I've taken it as the average global surface temperature for 2019. I've also made the assumption her predicted change relates to the last year of the prediction. That is, her prediction of 0.5 cooling is that in 2050 the average global surface temperature will be 0.5C colder than it was last year.

I've simplified the predictions by assuming a steady change from 2019 to the final temperature predicted, based on the above.

The charts are below. Not up to my usual standard with captions and labels, as I've not got time for that. Each chart shows the actual mean global surface temperature to 2019 based on NASA GISTEMP and is in Celsius.

First, the annual temperatures, with Judith's predictions. This chart also shows the linear trend line from mid-1970s to 2019 i.e. from the most recent change in trend to the present (0.19 C per decade).

Next her "warmest" prediction, as a decadal chart:

The "moderate" prediction as a decadal chart:

And the "coldest" prediction as a decadal chart:

If you're wondering why the next decade in all of them is warmer than the previous actual, it's because of averaging over the decades and the fact I've assumed a steady change with Judith's predictions.

Feel free to add your two bobs worth in the comments.


  1. One tiny quibble, or maybe a judgement call.

    Your first assumption is to continue from the 2019 value. I would start first with a different first assumption: Use the predicted value from your trend line.

    Why? Well by starting at the actual value you are actually adding a small constant (looks like about .1 or so) to Curry's prediction of rise over the whole period (making it harder for her to be correct...not that, that is the issue here).

    The reason I bring this up is because some years ago I spent a lot of time with some denier or other (forget who) who was "debunking" Hansen's 1980's work by doing the precise same logic as above. But it just "happened" he always wanted to start his prediction from a high point rather than a trough. That the specific first year was an el Nino year and so this meant that he was inadvertently or otherwise adding an unobserved constant to Hansen's work appear to be much farther off than it was.

    Basically trends fluctuate less than individual values.

    1. You're right of course, jgnfld. I wrote this in something of a rush as you can probably tell.

      You're also right that it probably doesn't make much difference. Also, last year may not be a "high point". There was no El Nino to force it up (not if you include the measures BoM uses).

      Anyway, my out is that I did put in all the assumptions. Plus, I don't think Judith gave any explanation of what she based her predictions on - whether last year, the last ten years, the trend or whatever.

      I'm not making excuses for myself. It would have been better if I'd used the trendline rather than a single year, but what the heck :D

    2. ABSOLUTELY no excuse called for. Not my point at all. And yes, the step change you may may possibly have built in with your assumption is clearly identifiable BECAUSE you took the time to spell things out...Unlike many instances from other sources which you've pointed out for us in the past.

  2. I dont suppose she is accepting bets? I could do with some more income...

    1. Why not ask her, Phil. I love it when people win their bets against deniers as they almost always do :)

    2. If she really believed in her prediction then she would find it just as likely that the actual temperature will fall below her median as above. Bet that it will fall above. Give her odds. 2:1 should be an even bet from her point of view, so give her 3:1. There is no way you can lose.

      My guess is that she would not accept this bet at any odds because she knows there is no chance it will only warm 0.11 C over 30 years.

    3. I'm mistaken. 1:1 would be even odds. Give her 2:1.

  3. Looks like a normal Judith Curry post, the subtext is always "we don't know so under no circumstances should we do anything that could *possibly* mean less money for fossil fuel billionaires."

    It's interesting she ends with:
    "the natural climate variability may help slow down the warming over the next few decades, allowing for time to make prudent, cost effective decisions that make sense for the long term."

    In this case society would underestimate climate risks and would probably take less (and less cost effective) action. My generation would get fisted, but the fossil fuel billionaires would get more money.

  4. Atomsk's Sanakan's comments are pretty funny and well referenced back to past claims by Judy Curry. Judy has not been responding like a scientist who follows the evidence and admits errors.

    1. That was excellent work by Atomsk's Sanakan in the comments there. Judith's excuses were lame and wrong. She doesn't know much about most aspects of climate science IMO. (Her main sources in her article are fringe at best, from people most regard as deniers.)

    2. This comment has been removed by the author.

  5. Is she publishing this in a respected peer-reviewed journal anywhere?

    1. In his 2010 profile on Curry, Michael Lemonick notes that, though Curry does not dispute the science produced by the IPCC (e.g. that the planet is warming, that human greenhouse gas emissions are largely to blame, or that the worst-case scenario could be catastrophic), she has major critiques of the IPCC as an organization. She said that she "does not have confidence in the process" due to the use of non-peer-reviewed papers.

    2. Hi PG :)

      BTW - I don't think Michael Lemonick would say the same in 2020, or not if he'd read her blog or her testimonies to the US government these past few years.

    3. Hi Sou. I have been absent because I became traumatised by AGW.
      My son who is now 22 has rehabilitated me. He is a loud climate bulldozer in Sydney and I expect soon nationally.

      But here's the thing. I hid the truth from him because I did not want him to be start adult life in fear.

    4. I hear you about being traumatised. I don't know if it's me, but feelings on social media appear to be ramping up. The climate prognosis hasn't changed but I'm sensing almost an air of hysteria which may not, or may, help matters.

      I think more people are waking up to what we're doing to the world, and people who've long been urging action are getting frustrated and anxious as what we've been warned would happen is happening more often.

  6. What's interesting is about her analysis is that the uncertainty is entirely in one direction. While volcanic activity has been high in recent decades, neither has it been zero. Solar activity has been below the maximums observed in the satellite era, so that it can only go lower is clearly inconsistent with observations.

    This is pretty much Curry in a nutshell, that is, "there is unknowable uncertainty in the system and the sign of that uncertainty is known" isn't a self consistent argument.

  7. I would pay cash to get her student ratings at Georgia Tech.


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