Description of HadCRUT3 data file found at:

http://hadobs.metoffice.com/hadcrut3/diagnostics/global/nh+sh/monthly

The data files contain 12 columns: 

Column 1 is the date.
Column 2 is the best estimate anomaly.
Columns 3 and 4 are the upper and lower 95% uncertainty ranges from the station and grid-box sampling uncertainties.
Columns 5 and 6 are the upper and lower 95% uncertainty ranges from the coverage uncertainties.
Columns 7 and 8 are the upper and lower 95% uncertainty ranges from the bias uncertainties.
Columns 9 and 10 are the upper and lower 95% uncertainty ranges from the combined station and grid-box sampling, and coverage uncertainties.
Columns 11 and 12 are the upper and lower 95% uncertainty ranges from the combined effects of all the uncertainties.