Update 2/7/17: I used the wrong GISS data (land only) in the comparison as pointed out by @cce! Agreement now is reasonably good for all temperature series.
This is my crib sheet for comparing temperature anomalies across ground and satellite data. Temperature anomalies are usually (but not always) defined relative to a baseline 30 year ‘climatology’. This simply means that a 30-year average temperature for each month is calculated at each location. The anomaly is then the difference of the mean temperature from that monthly ‘normal’. First here is a table showing which baseline each group uses.
|NASA GISS||1951 – 1980|
|Berkeley (BEST)||1951 – 1980|
|Hadcrut4.5||1961 – 1990|
|NOAA||1971 – 2000|
|UAH||1979 – 2010|
|RSS||1979 – 1984|
This means that you can only compare temperature anomalies once they have all been normalised to the same baseline. In order to do that you must first calculate the 30 year average monthly temperature for the new baseline and then subtract it. These are the normalisation ‘offsets’. The UAH baseline 1979-2010 is the only one where all datasets have overlapping values. These are the offsets you need to plot all series together.
|Group||Offset for 1979 – 2010 baseline|
UAH clearly has no offset and H4-ST is my own Spherical Triangulation of Hadcrut4.5 stations. The offsets above should be subtracted from all anomaly values in each series. Here is an animation of the results.
The agreement across groups.
is good except for GISS. The ‘warming’ observed by GISS is far greater than any other temperature index and renormalisation does not change the slope. It is an outlier.
Shown below is the table of offsets needed to normalise all series to the same baseline as Hadcrut4.5. The satellite offsets have been deduced by simply using the negative of the average Hadcrut4.5 anomaly in each of their respective baseline periods.
|Group||Offset for 1961 – 1990 baseline|
Here is the comparison for all series plotted on the Hadcrut4.5 baseline. GISS does show the largest overall warming trend, but it is not an outlier.
You can check my values and derive new ones using this spreadsheet. I also cannot understand why there is not already some agreed IPCC renormalisation. However, I am pretty sure it would be the same as mine.
Note: This post was prompted after a twitter exchange with Victor Venema. 😉