1. HadCRUT4-gl.txt is a copy of:
http://www.cru.uea.ac.uk/cru/data/temperature/HadCRUT4-gl.dat
which is available among other files here:
http://www.cru.uea.ac.uk/cru/data/temperature/
and explained here:
http://www.metoffice.gov.uk/hadobs/hadcrut4/
This file contains global average temperature anomalies from 1950 to (part of) 2014, based on combined land [CRUTEM4] and marine [sea surface temperature (SST) anomalies from HadSST3, see Kennedy et al., 2011] temperature anomalies on a 5° by 5° grid-box basis. The file consists of lines like this:
1850 -0.690 -0.279 -0.728 -0.565 -0.322 -0.215 -0.130 -0.234 -0.439 -0.455 -0.191 -0.265 -0.374
1850 22 20 18 19 18 20 22 22 23 23 24 25
1851 -0.295 -0.346 -0.468 -0.441 -0.304 -0.189 -0.216 -0.159 -0.111 -0.054 -0.021 -0.056 -0.219
1851 23 22 20 21 20 20 21 23 18 20 18 20
The year is followed by 12 monthly temperature anomalies, followed by an annual temperature anomaly, relative to 1961-1990. The year is then repeated and followed by 12 numbers which are the corresponding data coverage as a percentage of the Earth’s surface area.
2. HadCRUT4_monthly_temperatures_1850-2014.csv is a file built from the previous one, containing just 1968 = 164 times 12 numbers, which are monthly temperature anomalies from 1850 to 2013.
3. HadCRUT4_monthly_temperatures_1850-2014.jpg is a plot of these temperature anomalies.
4. HadCRUT4_monthly_temperatures_1850-2014.png is a nicer plot of the same thing, made by Alok Tiwari.
Items 5-9 were made by Blake Pollard:
5. TempAnomaliesPlotsWithAndWithoutTrend.jpg is a plot of the same temperature anomalies showing a linear trend line, and a plot of the "detrended" temperature anomalies - that is, with the linear trend subtracted.
6. DetrendedNotSmoothedFFTModulus.jpg is a plot of modulus of the Fourier transform of the detrended temperature anomalies.
7. ZoomedInDetrendedNotSmoothedFFTModulus.jpg is a zoomed-in version of the image in 6.
8. DetrendedSmoothedFFTModulus.jpg is a plot of modulus of the Fourier transform of a smoothed version of the detrended temperature anomalies. Smoothing tends to damp the Fourier transform at high frequencies.
9. ZoomedInDetrendedSmoothedFFTModulus is a zoomed-in version of the image in 8.
Blake Pollard writes:
If I am interpreting the results correctly, that first big peak after the low-frequency stuff is at about .0834 in units of 1/months. This corresponds to a 11.99 month period, so a year. The next peak is at about .1646 1/months or at about a 6 month period.
There is too much going on at low-frequencies. If you look at the 'ZoomedInDetrendedNotSmoothedFFTModulus', you'll see a plot zoomed into low frequencies. A two year period would be around .042. There are some things going on there but nothing compelling. The two big peaks above .4 right next to each other are at a frequency of .023 1/month or 43.25 month period.
Items 10 and 11 were made by Blake Stacey:
10. HadCRUT4_global_monthly_temperatures_1850-2014_stacey.png is is a plot of the temperature anomalies, essentially the same as items 3 and 4, but with the x axis more conveniently labelled by years.
11. parse-HadCRUT.py is the python program Blake wrote to do this. It is well-commented and illustrates some useful features of the language.