Significant trends

I see again a fuss at WUWT from Lord Monckton about "no significant warming for seventeen years and four months". I note wryly that the recent Keenan kerfuffle was about the Met Office answering a question about significant rise by citing the exact same statistic - whether with a AR(1) model the linear trend could be distinguished from zero. People wanted Dr Slingo sacked etc. But here we're back as usual - WUWT is  citing that very same statistic.

But it is indeed a fairly pointless statistic (the Met Office produced it on the insistence of a contrarian Lord). Statistical significance is important when you are trying to deduce some proposition from data. You need to know if your deduction could have arisen by chance.

But that's not the case here. We believe temperatures will rise because we've burnt a huge amount of carbon and boosted air CO2 by over 40%. And we look to temperatures and see a rise. Whether noise could have caused it is not the point; if you have a theory that predicts a rise and you see a rise, that's the best you can expect from the theory.

"Significant rise" relates to the wrong null hypothesis. You can only disprove a null, and a failure to disprove that trend is zero is not a very interesting result. It could just mean a not very powerful test. The logical question is - OK we expected a rise and we see a rise - is it the right amount? That is, can we reject the null that there is a trend of the expected magnitude?

That's the proposition that Lucia keeps testing, and though I argue there about whether what she tests is the actual AGW prediction, it is a test that makes sense.

Anyway. I'm sure that we'll hear more about no significant warming for x years, so I thought I would try to say something about the future course of x. It doesn't have a lot of degrees of freedom. And of course, it's as much affected by the ups and downs of temperatures in the '90s as those of today.

I'm basing this on the comprehensive trend plots I started a year or so ago.

TempLS global temp up 0.06°C in May

The TempLS monthly anomaly for May 2013 was 0.480°C, compared with 0.418° in April.

A climate blog reader

Google Reader is kaput at the end of June. I had been lazily eyeing alternatives, but I had also been looking into RSS systems, and it seemed that I could fairly easily write my own. It's a bit like re-inventing, but there are advantages. I used Google Reader a lot, though its limitations were painful. Improved searching is one aspiration. But if you read the feeds yourself, you can accumulate as much back data as you like.

Anyway, I found along the way that I could fairly easily compile an updated searchable list of comments on the main blogs that I was reading. My first attempt is below the jump. So far, I just have a few days data on the main Wordpress blogs. There are a lot of idiosyncracies, so I'll gradually extend it. When it has stabilized, I'll promote it to a page.

Draggable graphs

In the climate plotter a large amount of climate data could be plotted on an adjustable scale. There were bars on which you could click to move and expand the graph vertically and horizontally. Curves with different units could be moved independently. This is all based on the HTML5 canvas.

The bars were a bit clunky. I've been experimenting with mouse dragging. I had thought it would be slow, but it isn't. I'm planning to use it routinely in plotting, and for the climate plotter, and to post the code that enables it. Entering different data is easy.

Here's an example which I'll include in the monthly data tracking. It looks like just the last three years of monthly index data, similar to a graph that is currently shown. But it's backed by data back to 1850, which you can see by dragging back, and shrinking the scale if you want.

Jaxa Arctic Sea Ice - active polar plot

It's the time of year for tracking ice. I have kept current plots and tables of Jaxa daily reports. This year, there will also be daily updated movies of high resolution Arctic SST, both last 50 days and full year.

But I wanted to update the plotting methods using some of Javascript active features. I've made a polar plot, where the ice extent is represented as distance from the centre, and time progresses by angle, just as with a clock. Various parts can be magnified. When it has settled, I'll include it in the current page.

April GISS Temp down by 0.08°C

GISS LOTI went from 0.58°C in March to 0.50°C in April (back to February level). TempLS was fairly steady, satellites mixed.

Climate of the Past fails Fourier test

This is a belated post. I'm writing about a paper by Ludecke et al which was accepted in February by the EGU online journal "Climate of the Past". Eli wrote about several aspects, including data quality and how the paper made it to acceptance. Tamino gave a definitive mathematical takedown. Primaklima has a thread with some of the major local critics chiming in.

So what's left to say? And why now? Well, Ludecke had a guest post at WUWT a few days ago, promoting the paper. While joining in the thread, I re-read the online discussion, and was surprised at the lack of elementary understanding of Fourier analysis on display. Surprisingly, the guest post was not well received at WUWT, at least by those with math literacy.

I expect that notwithstanding this negativity, the paper's memes will continue to circulate. It comes from EIKE, a German contrarian website. And they have been pushing it for a while. Just pointing out its wrongness won't make it go away.

So here my plan is to redo a similar Fourier analysis, pointing out that the claimed periodicities are just the harmonics on which Fourier analysis is based, and not properties of the data. Then I'll do a similar analysis of a series which is just constant trend; no periodicities at all. Ludecke et al claim that their analysis shows that there is no AGW trend, but I'll show the contrary, that trend alone not only gives similar periodicities, but is reconstructed successfully in the same way.