I really thought I might only write a few posts here, but it’s hard to avoid commenting on what is said on Watts Up With That (WUWT). Bob Tisdale, in a recent post called Dana Nuccitelli misleads and misinforms in his first blog at the Guardian, has again referred to Skeptical Science’s Escalator. The point behind this graphic is to illustrates that global warming is a long-term trend. In other words, is there a tendency for the total amount of energy (as measured – in the case of the planet’s surface – as a temperature) to increase with time. You can’t choose a short period in which the trend is flat or negative to claim that global warming isn’t happening. You should consider as much of the relevant period as possible. If we think global warming has been happening for the last 40 – 50 years, we should consider the full 40 – 50 year period. When we do, as the graphic illustrate, there is indeed a positive trend indicating that – on average – the amount of energy in the climate system is greater today, than it was 40 – 50 years ago.
Bob Tisdale, in the above post, says (and I quote)
“The Escalator” by definition is an exercise in cherry picking. Let’s illustrate, with the same data used by Nuccitelli, how global surface temperatures actually warmed without cherry picking the time periods. We’ll simply highlight 3 naturally occurring events, and use them as start and end years for shorter-term data illustrations.
Just because you’ve chosen periods defined by 3 naturally occurring events doesn’t mean that you haven’t cherry-picked. Below is one of the figures that he produces. For some reason, he seems to think that this proves that global warming is a consequence of natural events (ENSO cycles). But all he’s done is to cherry-pick the start and end points so as to start at a high-point and end just before the next high-point so that the trend in each interval is flat. However, if you look at the full time interval it is fairly clear that there is a net warming trend. Given that ENSO cycles cannot produce energy from nowhere, where is this energy coming from? In an earlier post I posed a couple of basic questions for Bob Tisdale. I think these are fairly fundamental questions and I’d be quite pleased if he tried to answer them.
I’m really quite amazed by this. Bob Tisdale is – without irony – trying to illustrate that global warming is natural by doing precisely what climate skeptics have – in the past – been mocked for doing. I don’t understand how it isn't obvious that all he's done is cherry-pick his start and end points to get the result he would like to get. The only way one could show that global warming is not happening (without actually measuring the energy imbalance directly) is to show that over a long enough time period the amount of energy in the climate system remains flat or decreases. If one can show that it is increasing, then global warming has to be happening. Whether or not there are variations due to other natural events is irrelevant. If the total amount of energy is increasing with time, then global warming is real and this should not – in my opinion – be a controversial statement.