I’ve been doing quite a lot of cycling during our holiday, and today cycled over Duke’s Pass (a classic Scottish cycling route, apparently) and then cycled back around the Loch on the banks of which we’re staying. Very nice, but very tiring. Given that I need a bit of a break, I thought I might highlight the Global Warming Policy Foundation’s (GWPF’s) latest illustrative series. A previous one was how to whine like a 7-year old. This one appears to have a running title of how to lack irony and self-awareness. After years of highlighting anyone who suggested that global warming stopped in 1997/1998, they finally say
When estimating trends, especially for such short periods in a noisy data set such as global surface temperatures, care must be taken with start and end points as they can affect the trend obtained.
Of course, the only reason they’ve done so is because Karl et al. (2015) have suggested that the trend since 1998 may now exceed the confidence interval (i.e., it might be statistically significant, for those who think that’s appropriate in this circumstance). I guess it’s good that the GWPF now recognise that one should take care when estimating trends over short time intervals in noisy data. It would have been much better if they’d recognised this when the trend did not exceed the confidence interval, and they were using this to claim that global warming had stopped.
The GWPF report also includes a discussion on statistical significance by Professor Gordon Hughes, from the University of Edinburgh!!!. The only time I’ve encountered Gordon Hughes was when Nic Lewis repeated some of what he’d said about the Marotzke & Forster paper. In that instance it was clear that Gordon Hughes did not understand the physical sciences particularly well. His most recent foray into this topic would seem to further confirm this lack of understanding. His basic argument seems to be that to estimate the variability in 17 years trends, one should use all possible 17 years trends. This may be true if all 17 year time intervals were essentially equivalent, apart from some kind of random variability, but they’re not. It’s true that the variability for different 17-year time intervals isn’t the same, but that doesn’t change that the variability in a particular 17-year time interval is determined by the data for that time interval, not by the data from a large sample of other 17-year time intervals.
If anything, what Gordon Hughes has illustrated is that it is quite likely that variability on 17-year timescales can mask an anthropogenic/forced trend. That’s why one should be careful of claiming that global warming has stopped if the time interval is short. It’s certainly not a reason for claiming that it has, as the GWPF has done, time and time again. In fact, one problem with over-promoting the Karl et al. result is that it’s not all that surprising that variability could have produced a slowdown in surface warming.
Anyway, that’s all I was going to say. There’s more that I could say, but the Wi-Fi here is very slow and I’m not even sure if this will actually post. It’s also why I haven’t included many links in this post. I’m also struggling to access the comments, so apologies if I don’t respond, and let’s keep everything civil and polite.