Breakdown of effects of GHCN adjustments.

In a previous post, I showed how running TempLS with unadjusted or adjusted GHCN station data made a small difference to the final global average. That is useful to know, because some say that AGW is a creature of GHCN adjustments. This is certainly not true.

That analysis can be extended. I can trace the contribution to this small adjustment effect from various categories of stations - by continent, rural status, or airport status. And as before, it shows the difference by year, or effect on trend (to present time) by year.

A useful addition to the present post will be some trends calculated for land only in a NOAA paper by Lawrimore et al, 2011, Table 4 (h/t Victor Venema):

	v3 Uncorr	v3 Corr
1880–2010	0.61°C/Century	0.79°C/Century
1901–2010	0.70°C/Century	0.91°C/Century
1951–2010	0.16°C/Decade	0.18°C/Decade
1981–2010	0.27°C/Decade	0.27°C/Decade

Note the change of units (in the original). I got an approx land only difference of 0.17°C/Cen for 1900-2014 by dividing the global value by the land area fraction. That was pretty rough; the value in this post is more accurate, and agrees well.

In this post, I'll start with the usual active plot - see here for guidance. I've added a new "Norm" button. This allows you to toggle to a mode where the average adjustment for each category is calculated. The initial mode gives the contribution of that category to the global average. I think that is most useful, as it is area weighted. The category average can show high average adjustments for relatively rare stations. I'm using TempLS mesh exclusively; the grid style allows too much mixing between categories.

As usual with the active graph, you can select the set to show, move and zoom the graph, and show the numerical data. Then I'll show some ordinary graphs comparing the categories.

Here is the active plot. You can click on Trendback to togle a mode that shows trends to present, and on Data to pop up the numbers you see on screen.

Global with urban/rural breakdown

Here is the plot. All have a slight smoothing over 3 years. Note that all these plots can be generated on the zoomable active plotter, along with the associated trend graphs.


So you can see that the total global contribution is negative to about 1970, then positive. This has the effect that the contribution to trends from about 1960 onward is actually cooling. These are the trends that are vigorously debated as possible evidence of AGW. They are not enhanced by adjustment - on the contrary.

Before 1970 the adjustments "cool the past", by up to 0.05°C. However, on a land basis, that is up to 0.2°C. That is representative of the maximum average adjustment.

A virtue of the left style is that it is additive. So urban adjustments make up the larger part, but not by all that much.

There is an interesting sharp rise to about 1975, and then a decade plateau. We'll see more of it. It seems here associated with rural. My theory is that it is an airport effect, and may be associated with the move of some rural classified stations to airports.

There is also a WW2 effect, principally associated with Mixed (between rural and urban). Again I think it may have been connected with the moving of civilian stations to military airports, and maybe back again.

Breakdown by airport status

Here both of those features are markedly associated with airport status (hence my theory). Despite what you sometimes hear, adjustments to airports are a relatively minor net contributor. Note that the GHCN inventory ratings that I use refer to current conditions. Many "airports" have century plus records; they obviously weren't always airports. Some adjustments probably relate to the time when the station was originally transferred to the airport.

Breakdown by continent

Well, as you might expect from recent fusses, South America has the most negative adjustments. Africa is mostly positive. Less adjusted are Europe and Oceania (BoM and NIWA take a bow!).

Special cases

Finally, I'll show CONUS (continental US) and the Arctic. There has been a lot of fuss in recent times. The Arctic adjustments have been passionately excoriated by Booker of the Telegraph.



Well, as you'll see, the Arctic has made very little contribution to the global average, and it is quite flat. On the right, the average adjustment is also quite low (and again flat in trend).

CONUS, on the other hand, has the highest average adjustments (also noted here). That is mainly TOBS. Because CONUS is a smallish fraction of total land, the effect overall is modest, and also not so strong in trend. As previously noted, the adjustments reach a minimum in the 1930's.