Monday, November 21, 2011

Giss, TempLS and the October GMST

Late this month, so GISS is already out. Both GISS and TempLS recorded an almost identical small rise in the October Land/Ocean anomaly. TempLS was up from 0.424 to 0.486°C, and GISS up from 0.48°C to 0.54°C. The graph is below the jump::

Observed SST and model trends

Bob Tisdale has a post at WUWT comparing sea surface temperature trends predicted by a mean of IPCC models versus HADISST observed trends. He notes that the 17 year (204 month) trends do not agree very well.
Update - I've added an appendix showing how the all-trend plot can be used to understand the arithmetic behind the current drop in 17-year trend.

Tamino pointed out that the model mean that Bob used had far less variability than individual model runs, and could not be expected at all to reproduce the decadal variation of observations.

You can see some of this in the following plot, which includes two other SST measures, HADSST2 and HADSST3 in the mix. These of course are far more interdependent than model runs, but you can already see that the model mean is within the variation of the observations, with the exception of an oscillation between about 1930 and 1960.

I'm interested in this, because I have been writing a series of posts here, here. and here, which try to give a wider view of how calculated trends are part of a larger picture, which can indicate whether the choice is special in some way.

To see decadal trend variation in greater breadth, I made an interactive plot similar to the one described here. It's below the jump.

Wednesday, November 16, 2011

A picture of statistically significant warming.

This is the third in the series of plots showing color maps of all possible trends that can be derived from a dataset. The first post was designed to show how noisy short-term trends were, and how you could pick almost any color, representing a trend value, and find a period where it applied. But with some Javascript enhancement, it's also a good way of visualizing trends on a graph.

The scientific damper to choice of trends in a noisy signal is the significance test. So I've adapted the figures to show significance. I'm using the device of transparency - the colors just fade away as significance is lost. There is a small change at 99%, a big drop at 95% and a small further fade at 90%. The small changes are hard to see. The test is whether the trend is significantly different from zero. Colors fade when either the period is short or the estimated trend is in fact close to zero.

The data here are monthly temperature anomalies, so there is correlation, which affects significance. I've used the Quenouille correction for loss of dof. It gives results very close to AR(1) modelling. I'll give details.

I have included two new series - the NOAA land only index and the HADSST2 sea surface temperature. You can choose the series and time intervals by using the radio buttons on the right. I have redesigned the plot to make full use of the screen space. Because it overwrites the sidebars, I'll keep it below the jump.

Sunday, November 13, 2011

A numbers puzzle.

OK, this has nothing to do with climate. But it's connected with the trends gadget. I made a nudger that looked like this <<<<>>>>. If you click on the center symbols, you nudge by one month. Next out by 2, then four, and in this version, the outermost move by 8.

Well, suppose the sequence of symbols continued, in powers of 2, as far as needed. How far can you be sure of being able to move with, say, 2, 3, 4 or 5 clicks. More precisely, what is the least number that requires n clicks.

For n=2, it's 3. For n=3 it's 11 (8+2+1 or 16-4-1). But 4? 5? Can anyone think of a rule?

I can think of an upper bound for any n. It's less that 4^(n-1). But not a general formula.

Friday, November 11, 2011

A JS gadget for viewing temperature trends.

In my previous post I showed a map of all possible trends calculated over sub-time intervals of a period, with a mechanism for selecting different datasets and periods. Since there seem to be ongoing interest in viewing trends, I thought a useful Javascript gadget could be developed from that.

Now when you select a dataset/time combination, a corresponding time series plot is displayed, with two colored balls representing the start and end of each trend period. The numerical data are displayed on the right. There are several ways of controlling the horizontal position of the balls:
  • You can click on the colored triangle. Each position represents a start/end combination, so the balls will move to the endpoints of the fitted regression line, and the slope and locations will appear on the right. It's a realisation of the color on the plot, and should correspond.
  • You can move the balls by clicking on the red or blue bars on the graph.
  • You can nudge, for fine control, using the <<<<>>>> device of the appropriate color. The outside symbols move the ball of that color by 8 months, the next by 4 and the innermost by 1.
Update: It seems to be working now.
Well, it almost works. Unfortunately, on this blog system you can't test JS in the editor - I have to go straight from the home computer (where it worrks) to live. In fact everything is working except the movement of the balls. In particular, you can click on the color plot and the numerical values will appear on the right. The issue with the balls is that I have to move them by absolute position, and so I have to find out what Blogger containers they are in. We'll get there.
Update. I've posted this at another site here. It seems to work correctly there. It's possible Blogger just isn't going to let me set the balls in motion.


Monday, November 7, 2011

GMST trends - a cherrypicker's guide.

I've developed the diagram of this post into an interactive trend-viewer here.

With the conversation about the new BEST data, there has been an uptick in the posts showing plots from WoodForTrees with trends proving something or other. Here is a recent duel.

So I decided to expand the plots from the previous post to maybe make all this redundant. You'll see a plot of all the popular time intervals, with trends presented in a colorful array. Now all you have to do is spot the color you like, and look up the endpoints on the axes. Or if your disposition is wonkier you can try to spot patterns in the way the trends vary.

Some math details - I've taken each of nine indices and done an OLS regression of the monthly temperature against time for each pair of start and end points an various ranges. No prior smoothing, no annual averaging. There is a little colored square indicating the trend, in °C/century, for each pair. I haven't included periods shorter than four years. I've used rainbow colors, except for two ranges which help to calibrate by eye. These are zero trend, in gray, and 1.7°C, representing a recent average, in brown.

The plot itself is an interactive compendium of 36 images, for the 9 datasets and four time ranges. The times are from 1999 to present, 1989 to present, 1960 to present, and 1901 to present. They are presenting different fragments of the same trend array. I chose 1999 to present a popular contention at the moment that over a decade the trend is zero or less. For the land/sea indices there are certainly ranges for which that is true - I think this plot gives a fuller picture.

To use the interactive aspect, you can click on either of the legends in red to get any combination of index and time. Your current choice will be shown in black. As with all these plots that I do, the images are downloaded when requested, so when you first click there is a short pause - however, when you revisit that image, it's now in cache.

Below the jump, I'll say a bit more about some stationary images.

Saturday, November 5, 2011

Stopped warming? Paused?

More in the saga of the BEST data and whether "there is no scientific basis for saying that warming hasn't stopped" (Judith Curry). Or in the latest from Judith
"Has the rate of warming continued unabated, or has there been a pause in the warming?"

Judith has now offered a criterion: "Here I define “pause” to mean a rate of increase of temperature that is less than 0.17 – 0.2 C/decade."
Stopped means below zero. Now you might think that, with the short periods involved, there would be some notion of significance involved. But no:
"Note that the short time scales considered here preclude determination of a statistically significant trend at the 95% confidence level, although lack of statistical signficance does not negate the existence of a pause as defined here."

Well, it occurred to me that if any drop, significant or not, below, say, 0.17C/decade is a pause, then we'd be seeing a lot of them over the years. So I thought I would check that out.

The period of time Judith and others is looking at is about ten years. So lets look at ten year periods in the recent past, and see how many "pauses" show up.