Thursday, June 9, 2016

Never Cry Wolf! The Worst Climate Prediction Ever Made

If you cry wolf, and the wolf doesn't come, you'll make a fool of yourself. But it will be much worse if you don't cry wolf, and the wolf comes.


Professor Nicola Scafetta, showing his 2010 predictions for global temperatures (from Meteo Live News). These predictions turned out to be spectacularly wrong. 


The debate on anything that has to do with the future often becomes a peculiar version of the story of "Crying Wolf". Assume that somebody cries wolf and that the wolf doesn't come. Then, someone else will often conclude that wolves don't exist (or are something nobody should be worried about). Something similar occurs in areas such as climate science when past uncertainties are taken as indicating that climate change does not exist (or is something nobody should be worried about.)

Truly, it is a perversion of logic, but it has its reasons. Suppose that the appearance of wolves is relatively rare; then, even though you may know nearly nothing about wolves, it is a safe bet that you will be much more popular with shepherds if you tell them that the wolf won't come. And, normally, you will be able to claim that you were right; except when the wolf comes, of course, But, in that case it is likely that shepherds will be much more worried about saving their sheep than about chastising you for your incompetence in wolf matters.

Something similar seems to be happening with climate change where plenty of people, usually knowing very little about climate science, tend to reassure people that climate change doesn't exist or that it is nothing to be worried about. Inasmuch as waterfront houses are not normally washed away every week by hurricanes and sea level rising, these reassuring predictors can claim to have been right,

But sometimes even doomslayers may have a bad time when they try to make quantitative predictions. One remarkable case is that of Nicola Scafetta, who attempted to use a sophisticated statistical treatment (aka: let's torture the data until they confess) to prove that global warming is mainly caused by long-term planetary cycles. On the basis of his models, in 2010, he predicted that global temperatures should have remained constant or should have been going down; while in 2012 he predicted that temperatures should have been growing at a much slower rate than predicted by the standard climate models. On the basis of these predictions he gained a certain notoriety in some circles.

Well, if there existed a prize for the worst climate predictions, I think these ones by Scafetta could legitimately concur for it. Global temperatures refused to follow his prediction and are actually exceeding the result of the IPCC models that Scafetta had criticized.

Judge by yourself; below, you can see the results presented by Scafetta in 2010 (N. Scafetta. I cicli climatici e le loro implicazioni. Periodico semestrale dell’Associazione Normalisti. n.2 dicembre 2010) (see also this link). Recent temperature data added in red.


Some more recent predictions by Scafetta are a little better, but still widely off the mark (recent  temperature data added in red)


So, here is the conclusion: since we have solid physical evidence that wolves exist (unlike dragons and unicorns), you'd better pay attention to those who tell you that your sheep could be in danger. In the same way, since we have solid physical evidence that greenhouse gases cause warming and that their concentration is increasing, you'd better pay attention to those who tell you that your waterfront property is in danger (and not just that!)

Acknowlegement: Stefano Caserini prepared the figures shown in this article.


Note: this article was prompted by a debate that I had today with Nicola Scafetta at the AIGE-IIETA 2016 conference, in Naples. In his talk, Scafetta spent most of his time criticizing the standard general circulation models, saying that they don't reproduce well the historical data and that they are affected by huge uncertainties. He said that these models much exaggerate the climate sensitivity to CO2, although he stated that he does not deny that greenhouse gases have an effect on global temperatures. Then, he showed the results of his models compared with historical data, but always stopping the comparison with 2012 or 2013. He also said that according to some new work he has performed, he believes that Jupiter has a strong effect on the earth's temperatures. 

In my comment, I showed to the public the data that I am publishing in this post and I asked Scafetta how he can justify such glaring errors. Scafetta said that these are old results and that now he has better models. I countered saying that he can't change his assumptions every year and every year pretend to make reliable predictions. He reiterated that his model works now. Then, the moderator said that we had to stop and he recommended to everyone caution in believing models. And that was it!


7 comments:

  1. grande Ugo sei tutti noi!

    ReplyDelete
  2. Wow, he didn't include the recent El Nino. Once La Nina settles in, maybe you can revisit this ;)

    ReplyDelete
  3. "he believes that Jupiter has a strong effect on the earth's temperatures"

    Is Scafetta now an 'independent' researcher or did he end up with a position somewhere else after leaving Duke? (Somewhere else, one would have to assume, with lower standards.)

    ReplyDelete
  4. Mi mancava l'influenza di Giove sulla temperatura della Terra. Paragonabile, secondo alcuni esperti, a quella del Sagittario

    ReplyDelete
  5. oooooo it's all Theo Landscheidt. . . (look that up, you will not be able to stop laughing.

    ReplyDelete
  6. Ugo
    Sometimes one has to wonder if there are enough adults in the room!

    You know all this stuff of course but careful addressing of uncertainty is what a mature science is all about. You have said rightly in the past that climate science is such a mature science. It is hard to understand therefore that recent gross changes not seen for millions of years in climate forcing by non-condensing greenhouse gases, pre-eminently CO2 and CH4, can be so easily set aside in favour of pettifogging calculation. This particular maverick has not bothered to read and understand the careful literature and data.

    As I said, you know this stuff, but James Hansen in 2013 exemplifies the careful attempt to find and test data so that we might understand the very big picture. Really very suddenly, and remarkably, the ‘very big picture’ of aeons now includes us and our immediate descendents in time measured by the human life-span.

    Others might find this useful; Hansen et al:
    http://rsta.royalsocietypublishing.org/content/371/2001/20120294

    “Earth's response to climate forcings is slowed by the inertia of the global ocean and the great ice sheets on Greenland and Antarctica, which require centuries, millennia or longer to approach their full response to a climate forcing. …

    “… Climate models, numerical climate simulations, provide one way to estimate the climate response to forcings, but it is difficult to include realistically all real-world processes. Earth's palaeoclimate history allows empirical assessment of climate sensitivity, but the data have large uncertainties. These approaches are usually not fully independent, and the most realistic eventual assessments will be ones combining their greatest strengths. …

    “… We use the rich climate history of the Cenozoic era … [65 million years of rich data] … inferring climate sensitivity empirically. [Using improved calculations]… Finally, we use an efficient climate model to expand our estimated climate sensitivities beyond the Cenozoic climate range to snowball Earth and [to] runaway greenhouse conditions. [That is they model both directions of ‘runaway’ self-reinforcing – in one direction sufficient cooling causes the major greenhouse gas (GHG), which is water vapour, to condense out (“snowball earth” which existed in the very remote past), and in the other direction, runaway warming reinforces all major GHG emission including water vapour and has gross temperature and other effects, as in the PETM which happened about 50 million years ago.]

    “We hypothesize that the global climate variations of the Cenozoic can be understood and analysed via slow temporal changes in Earth's energy balance, which is a function of solar irradiance, atmospheric composition (specifically long-lived GHGs) and planetary surface albedo.

    “Estimates of climate sensitivity cover a wide range that has existed for decades [3 references to earlier climate science papers]. That range measures our ignorance; it does not mean that climate response from a specified state is stochastic with such inherent uncertainty.

    And so on …

    best
    Phil H

    ReplyDelete

Who

Ugo Bardi is a member of the Club of Rome and the author of "Extracted: how the quest for mineral resources is plundering the Planet" (Chelsea Green 2014)