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!


Ugo Bardi is a member of the Club of Rome, faculty member of the University of Florence, and the author of "Extracted" (Chelsea Green 2014), "The Seneca Effect" (Springer 2017), and Before the Collapse (Springer 2019)