Make that nine...

I’ve now added the Japan Meteorological Agency’s temperature series to the global temperature plots on the graph pages (you may need a browser refresh to see the latest versions):

Global monthly temperatures since 1970 -- instrumental estimates

Global monthly temperatures since 1970 — instrumental

In my view the JMA series doesn’t have any special merit, but it does appear to have been developed independently, so it might add some further confidence to the overall picture if that was required (it wasn’t).

JMA uses 5-degree latitude-longitude grid based averaging. They include their own sea surface temperature analysis (“COBE-SST“), which may be the source of their slightly spikier monthly temperature estimates, particularly early in the record. (NASA GISTEMP previously used their own unsmoothed SST series, resulting in a very spiky monthly profile in early years.)

The most important differences between the various instrumental temperature estimates lie with their effective coverage. This diagram from Sceptical Science tells the story (click for source):

Global temperature series coverage and recent anomaly pattern, from Sceptical Science

You can see that, like HadCRUT, missing data areas (mostly near the poles) are just excluded from the JMA average, with the effective coverage being even smaller than HadCRUT (about 85% of the globe). The result is an underestimate of recent warming, because the excluded polar areas are known to have been warming very rapidly. That may be one reason why JMA has been running a little lower than the pack in recent years. In my opinion series like GISTEMP, Cowtan & Way and Berkeley Earth are superior in that regard (because they attempt to fill the gaps), but the differences are slight. Refer to the notes on the graph pages.

One more time for emphasis — for the purposes of understanding where we’re headed this century, all the global temperature series are the same:

Simplistic temperature extrapolations

Simplistic temperature extrapolations


Because JMA only provides gridded monthly data for download, my plotting spreadsheet is now very large (23MB). It includes automated update macros for all series. You can download it here:

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