The longer I am involved in the global warming debate the more frustrated I am getting with the CRU temperature data. This is the one of the most commonly cited sources of global temperature data, but the numbers just don’t stay put. Each and every month the past monthly temperatures are revised. Since I enter the data into a spreadsheet each month I am constantly seeing the shift in the data. If it was the third significant digit it wouldn’t bother me (very much), but it is much more than that.
For example, I have two very different values for January of 2010 since September 2010. Here are the values for January based on the date I gathered it.
Sep 10th, 2010: January 2010 anomaly was 0.707 °C
Jan 30th, 2011: January 2010 anomaly is now 0.675 °C
That is a 5% shift in the value for last January that has taken place in the past 4 months. All of the initial months of the year show a fairly significant shift in temperature.
Oddly enough the yearly average seems to stay the same, but the monthly values that create the average are in constant flux. It seems that May of 2010 is the current transition point for the year. The latest data has the early part of 2010 as the cooler version, but past May the latest data is warmer than the earlier data. It is very frustrating to use data that is this unstable.
It just isn’t 2010 that is in flux. December of 2009 has undergone at least 3 significant revisions in the past 4 months.
Sep 10th, 2010: December 2009 anomaly was 0.411 °C
November 2010: December 2009 anomaly was 0.473 °C
Jan 30th, 2011: December 2009 anomaly is now 0.438 °C
This constant variation in the data makes comparing temperatures even a year ago impossible. According to the data available by the CRU, December of 2010 was somewhere between 0.151-0.213 °C cooler than 2009. The current data indicates that 2010 was 0.178 °C cooler than 2009, but it seems likely that this will also change in the months to come.
I am going to start saving the full revision each month and will be putting together future comparisons of what should be a stable temperature set. The changes might not seem significant, but the constant revision of global temperature data from the CRU is very concerning as it makes comparisons to past data slippery. If I can’t trust the data from December 2009 from the CRU, how can I possibly trust data from December of 1909?