Watt about the “escalator”?

A little while ago Skeptical Science produced a graphic that they used to try and illustrate the difference between short-term variations and long-term trends. It was called The Escalator and I include it below. As I discussed in a previous post, one problem with determining if global warming is happening (using temperature anomaly data) is that you can’t actually detect a statistically significant signal if you don’t consider a sufficiently long time period. This is simply an issue with the intrinsic scatter and not some problem with the data analysis. Something else that “The Escalator” was trying to illustrate is that even if global warming is happening, you still expect to see other variations – from solar variablity, ENSO – in the temperature anomaly data. There will be periods where the temperature anomaly might rise quite quickly and others where it might actually fall. What’s important is whether or not there is a underlying, long-term warming trend.

Graphic illustrating the difference between short-term signal and long-term trends.

Graphic illustrating the difference between short-term signal and long-term trends.

Now, I’ve been trying to be quite balanced when discussing posts on Watts Up With That, but a recent post by guest author Jan Zeman appears sufficiently inane, that I’m finding it difficult to not be particularly rude. The post is called Another “escalator” and compares temperature anomaly data with data showing solar variability. I include one of the main figures below. What the author appears to have added are some short linear trends that illustrate how the temperature anomaly varies on time periods comparable with the Solar cycle. The claim then seems to be along the lines of “AGW people seem to think the Sun doesn’t influence the climate, but look there is a clear dependence on solar variability”. Yes, everyone knows this. Noone is saying the Sun doesn’t influence the climate. However, what people are saying is that if the prime drivers of climate change were the Sun, ENSO, and other non-CO2 related processes, then we should see variability but the average should tend to zero. However, what can be clearly seen in the figure below is a long-term warming trend. The mean in 2010 is clearly about 0.5oC higher than in 1965. The author completely fails to point this out (unless I missed it) and seems to think that by showing that there is a signal that correlates with solar variability that they’ve someone disproved global warming. All they seem to have done is completely mis-interpret the figure below and ignored a very obvious long-term warming trend.

Figure comparing HADCRUT4 temperaturs anomalies with solar variability.

Figure comparing HADCRUT4 temperaturs anomalies with solar variability (credit : Jan Zeman and Wood for Trees.

The reason I’m always a little concerned about being too rude about a WUWT post like the one discussed here is that I worry that there is some subtlety that I’ve missed. This one seems so ridiculous that I can’t quite believe someone’s actually written this. I can’t quite believe that someone can produce a figure like that above and not realise that it illustrates precisely what Skeptical Science was trying to illustrate with their Escalator. To then use this to – in some sense – rebut Skeptical Science’s Escalator is remarkable. Given how ridiculous this seems to be, makes me worry that maybe it is actually incredibly clever and subtle and I’ve just misunderstood what it’s saying. If someone can convincingly explain why this is a clever and subtle bit of work, I’d be happy to accept that. Until that time, however, I have to conclude that this is someone who has basically proven the point they were trying to refute.

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2 Responses to Watt about the “escalator”?

  1. Paul Clark says:

    First, you have to remember that the sun is not the only factor and that the PDO was slightly up in the latter 20th century explaining at least some of the warming. The other thing is, you have to keep in mind the time integral of the sunspots. That is, a few consecutive high sunspot maxima in a row accumulate energy decade on decade. The four tall peaks all add to each other, while the current quiet peak on the right spells global cooling. More here:


  2. Paul, it really can’t be the Sun and, no, you don’t really have to keep in mind the time integral of the sunspots.

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