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Is something rotten in Alaska?

Via an open thread on Deltoid, I discovered a link to this article by E.M. Smith (reposted on Watt’s Up With That), looking at an odd map he’d managed to generate using a temperate map generator on the NASA GISS site. The map generator’s pretty fun to play with.

A map of the temperate anomalies can be generated by entering a base period and a time period. As I understand it, it then takes the difference in mean temperature between the baseline period and the time period and draws that on a map. Pretty simple, right?

Now, if you use the same base period as time period, you’d expect that the map anomalies would all just be zero, right? Well, almost. The default settings exclude ocean data, and E.M. Smith does not change that. Without the ocean data and a 250km smoothing radius, you actually get the following map:
Temperature anomalies, time period 1951-1980, base period 1951-1980

What’s going on? Well, the short answer is that in the GHCN data, 9999 is used as a flag value to designate missing data (see the help file at the bottom of a map page, “Missing data are marked as 9999.”). As there’s no ocean data, 9999 appears there. Now, probably those should be greyed out. In maps that have a different base period and time period, grey is used to designate regions that don’t have any data.

However, the simple fact that this was almost certainly just displaying a flag value didn’t stop the conspiracy! Oh no! Presumably, those 9999 values are leaking into the real graphs and causing all the red values in a map like this one:
Temperature anomalies, 2009, base period 1951-1980

Nice idea. So I ran with it. Don’t know how long this GISS map stays up on their site, but I just did 2009 vs 2008 baseline. The “red” runs up to 10.3 C on the key.

So unless we’ve got a 10 C + heat wave compared to last year, well, I think it’s a bug

So I think this points to the ‘bug’ getting into the ‘non-NULL’ maps. Unless, of course, folks want to explain how it is 10 C or so “hotter” in Alaska, Greenland, and even Iran this year: what ought to be record setting hot compared to 1998…

I’ll leave it for others to dig up the actual Dec 1998 vs 2009 thermometer readings and check the details. I’ve got other things taking my time right now. So this is just a “DIg Here” from me at this point.

It’s not the color red that’s the big issue, it is the 9999 C attached to that color… Something is just computing nutty values and running with them.

BTW, the “missing region” flag color is supposed to be grey…

Now, this is something of a leap: how unlikely is it that unusual values in the ocean would magically happen to manifest themselves as warming in Alaska or Greenland – let alone Iran – rather than in, oh, say, the oceans. Never mind the idea that a modest change in temperatures between two years is especially unlikely. But, even though this claim is extremely unlikely, let’s do a little investigating.

So, the question: was the temperature in Alaska during December 2009 really 4-12.3°C warmer than 1998, or are those 9999s leaking through? This is what NASA’s GISS temperature map shows:

Happily, this is an easy question to answer if you actually look at the data. I downloaded the unadjusted mean GHCN data for the various sites in Alaska (the headers are 42570398000-425704820011). I picked out all the sites which had data for 2009 (I’ve also uploaded the raw data for 1998, 2008, 2009 for these sites so you can look at them if you like). Note that the temperature values are in tenths of a degree.

Header Location Dec 1998 Dec 2009 Difference
425700260000 Barrow -186 -196 -10
425701330000 Kotzebue -173 -121 +52
425702000000 Nome -147 -94 +53
425702310006 McGrath -222 -182 +40
425702610000 Fairbanks -209 -198 +11
425702730000 Anchorage -100 -67 +33
425703080001 St Paul -22 -18 +4
425703160000 Cold Bay -22 14 +36
425703260000 King Salmon -125 -46 +79
425703610000 Yakutat -30 -22 +8
425703980000 Annette Island 19 12 -7

I’ve helpfully marked highlighted the differences for those sites in Alaska in the region which are particularly red in the map. There appears to be some sort of correlation. The average temperature difference between Dec 1998 and Dec 2009 at those sites is 4.9°C warmer. The darkest shade of red represents an anomaly of between 4 and 12.3°C, so, Alaska is properly represented. The average, Alaska-wide, was 2.8°C warmer.

It’s not just me. A commenter on Watt’s Up With That, carrot eater, points out:

First station I tried: Goose, Newfoundland.

is 8.6 C warmer in Dec 09 than Dec 08.

Let’s look for other stations in red splotches in Dec 09, compared to Dec 08

Egesdesminde, Greenland 5.1 C
Fort Chimo, Canada. 10 C

Looks like I found your 10 C difference between Dec 08 and Dec 09. Third station I tried. Hence, the range of the colorbar.

Let’s see what else we find.
Danmarkshavn, Greenland. 2.7 C
Godthab Nuuk: 5 C
Inukjuak Quebec: 6.6 C
Coral Harbor: 8.6 C

So I’ve found a bunch of stations that are between 5 and 10 C warmer in Dec 09 compared to Dec 08.

This is a fun game, after all. Let’s say I want to find the biggest difference between Dec 09 and Dec 98. There are lots of red splotches on the map, and the colorbar has poor resolution. So I’ll download the gridded data and have a look.

Scrolling past all the 9999s for missing data, and I find that I should be looking at some islands north of Russia. I try some station called Gmo Im.E.T, and I get:

Dec 09 is 12.3 C warmer than Dec 98. First try.

So, yeah, this “bug” turned out to just be a weather fluctuation. Colour me surprised.

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February 2, 2010 at 11:17 pm
  • April 6, 2010 at 11:57 pmDale

    The reason I come here a few times a week is because of the quality posts like this one. Please don’t ever change what you do or how you do it.

  • June 10, 2010 at 5:22 pmpell grants

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  • July 17, 2010 at 3:49 amOccupational Therapy

    nice post. thanks.

  • October 23, 2010 at 2:10 pmbadmash

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