Dig and Delve Part 2: Running Detrended Data

In my last post, Dig and Delve Part1, I showed how running trends are useful for showing the linear trend to any point in a dataseries, and that trends in different regions can be compared, after the first 10 to 15 years (120 to 180 datapoints).

In this post I use running trends to derive running detrended data, and analyse data for various Land regions using UAH anomalies.  Firstly, the following figure shows global mean UAH to November 2016 detrended using the current linear trend:

Fig. 1:  Global data detrended from linear trend

global-detrended-normal

This is the usual way to show detrended data.  It clearly shows where temperatures have been above or below the trend, however with each new data point the detrended data changes.  Running detrended data is calculated for each point as actual data minus  the running trend multiplied by the count of data points plus the running intercept.  Here is a plot of running detrended data and ordinary detrended data for Global UAH.

Fig. 2:  Global running detrended data and standard detrended data.

global-detrended-running-comp

After about 1987 they differ by less than +/- 0.1C, and UAH is accurate to +/- 0.1C anyway.   Note also that when temperatures are rising, running detrended data are greater and when falling, they are lower than standard detrended data.

The benefit of running detrended data is that they never have to be recalculated.  Historic detrended values are preserved.  As well, the running trend per month is conveniently not different from zero (which is why I showed it in Part 1 as degrees per 100 years by multiplying by 1,200), so it is easy to show the detrended data with a zero line.  The detrended value is also a measure of how much each month’s data has contributed to the trend- positive values indicate warming influence, negative values indicate cooling influence on the trend.

I now turn to using running detrended data to analyse what has been happening with Land data recently.

The following plots show running detrended data for Land TLT in the Northern Hemisphere.

Fig. 3:  Northern Hemisphere Land data detrended from running trend

nh-land-det

The large spike in February was followed by a plunge to October, but values in November have returned to trend.

Fig. 4:  Northern Extra Tropics Land data detrended from running trend

next-land-det

Similar to the Northern Hemisphere.

Fig. 5:  North Polar Land data detrended from running trend

np-land-det

Note how much North Polar data fluctuates.  However the Poles only contribute less than 7% to the Global mean.

Summing up:

  • Running detrended data never have to be recalculated, and historic values are preserved.
  • The detrended data show how much each month’s data has contributed to the trend at that point.
  • The recent plunge in Northern Hemisphere Land anomalies is nothing to get excited about as it is the recovery from a huge spike. The November value is still on trend.

The next in this series will use an estimate of discrete Extra Tropics (20-60 North and South) to look at trends and detrended data.

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7 Responses to “Dig and Delve Part 2: Running Detrended Data”

  1. michaelspencer2 Says:

    But! But! Where are the apocalyptic temperatures rising to a ‘tipping point’ where we will all be off to Hell in a handbasket unless we pay our dues to Al. Gore, James Hansen, Tim Flannery, David Karoly, etc. etc. etc.?

  2. MikeR Says:

    No sign of the apocalypse or a ‘tipping point’ in your figures above.

    The trends above are all flat. Amazing that data that has been detrended has no trend!

    Ken , I know you should not be held to account by those who comment here. It must be frustrating to have comments like the above posted on your site.

    Ken , wishing you an enjoyable new year.

    • kenskingdom Says:

      And a happy New Year to you too, and to all my readers. Michael, I think the running trend at zero might have confused you- that’s the trend per month. Multiply by 1200 to see the 100 year trend.

  3. MikeR Says:

    Ken, the running trend above looks very, very close to zero for the last point. Are you saying the last point of the North Pole is about 2.4/1200 =0.002 C? It is almost impossible to tell from your graphs. I am really puzzled why you would present the running trend line this way as you cannot tell without using a microscope what the actual trend is.

    If Michaelspencer above can do it with the unaided eye then I am mightily impressed. Actually it is totally impossible as the size of the embedded jpeg graphics is only 370 pixels high so 1 pixel in the vertical direction corresponds to 0.018 C. Trends of plus (or minus) 21 degrees C per decade would be required to displace the line up (or down) by 1 pixel. Now that would be an apocalypse!

  4. MikeR Says:

    Sorry, the last trend figure should be 21 degrees C per century of course! Despite this I think a trend this size, up or down, would still be apocalyptic.

    • kenskingdom Says:

      See the previous post (Part1) for trends per 100 years. Plots above are clearly labelled “deg. C / month”. As I explain above, this is not visibly different from zero, and I use it merely to emphasise the zero line.

  5. Dig and Delve Part III: Temperate Regions | kenskingdom Says:

    […] together ideas developed in previous posts- Poles Apart, Pause Updates, Dig and Delve Parts I and II– in which I lamented the lack of tropospheric data for the regions of the northern and […]

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