Comparison of CRU and GISS Temp Data
Posted by Jeff Id on December 10, 2009
A short analysis by Kenneth Fritsch on differences between land surface temperature datasets. I’m extremely busy tonight and have not been able to verify anything here, but am familiar with the quality of Ken’s work. I’m sure he’ll stop by to answer questions from time to time.
Also, reader Ian has an interesting reply with an email from Ed Cook. I want to discuss more in the future but am way too busy today. It shows the fear of doing what’s right in climatology– rather shockingly. It’s comment #52 here.
Guest post Kenneth Fritch,
For those of you who are looking for a complete refutation of global warming, I will disappoint. My point in this whole exercise is more subtle. I wanted to determine whether we could compare temperature series for regions of the globe and over certain time periods where the temperature difference would show statistically significant differences. As far as we know these temperature series are constructed using much of the same raw and perhaps adjusted data. These series, while used separately, like to advertise the fact that they closely follow one on another. I would think that to show statistically significant differences between sets would place uncertainty on all sets as we do not have an independent and absolute standard for comparison. Even smallish differences would place doubts.
To that end, I compared the data sets described below and measured the normalized differences over several global regions and mainly two time periods. I used CRUTEM3+HadSST2 and GISS 1200 km and GISS 250 km for temperature data sets of land and sea for comparisons from the link:
That link is very useful for extracting zonal temperatures from the globe. I used the globe, and the zones (around the globe longitudinally): 0-20N, 0-20S, 20N-40N, 20S-40S, 40N-60N, 40S-60S, 60N-80N and 60S-80S. Unfortunately when comparing polar regions, the CRU data set did not have sufficient data points to do a reasonable comparison. Why the GISS data sets had more data points (filled in?) I do not know at this time.
The results are listed below and a graph is linked here:
For the time period 1900-2008 for the globe we get the following statistical results:
The trend is from a linear regression of data set differences versus time and is in degrees C per century. The adjusted R^2 has its usual meaning. The probability that the trend could happen by chance is given by p carried only to 3 decimal places. The lower and upper trend values at the 95% CIs are listed.
Trend = 0.07; Adj R^2 = 0.26; p = 0.000; Low95% = 0.05; Up95% = 0.09
Trend = 0.02; Adj R^2 = 0.00; p = 0.265; Low95% = NA; Up95% = NA
There is nothing very different about these data sets except that the CRU-GISS1200 is significantly different – but not by much. However, when the difference time series are viewed as, by example in the linked graph above, an apparent step is noted around the mid 1940s. A trend from 1945-2008 yields some very significant differences for the globe as noted below:
Trend = 0.14; Adj R^2 = 0.34; p = 0.000; Low95% = 0.09; Up95% = 0.19
Trend = 0.17; Adj R^2 = 0.34; p = 0.000; Low95% = 0.11 ; Up95% = 0.23
Using these same methods the results below show the differences for the time period 1900-2008 (except where noted) and 1945-2008 for global zonal regions. Results are shown only for CRU-GISS1200. The differences between CRU-GISS250 while different were of the same magnitude.
0-20N for 1900-2008:
Trend = 0.05; Adj R^2 = 0.11; p = 0.000; Low95% = 0.02; Up95% = 0.08
0-20S for 1900-2008:
Trend = 0.15; Adj R^2 = 0.47; p = 0.000; Low95% = 0.12; Up95% = 0.18
20N-40N for 1900-2008:
Trend = 0.02; Adj R^2 = 0.01; p = 0.192; Low95% = NA; Up95% = NA
20S-40S for 1900-2008:
Trend = 0.17; Adj R^2 = 0.44; p = 0.000; Low95% = 0.13; Up95% = 0.21
40N-60N for 1900-2008:
Trend = 0.01; Adj R^2 = 0.00; p = 0.405; Low95% = NA; Up95% = NA
40S-60S for 1956-2008:
Trend = 0.44; Adj R^2 = 0.31; p = 0.000; Low95% = 0.26; Up95% = 0.62
0-20N for 1945-2008:
Trend = 0.16; Adj R^2 = 0.49; p = 0.000; Low95% = 0.12; Up95% = 0.20
0-20S for 1945-2008:
Trend = 0.20; Adj R^2 = 0.58; p = 0.000; Low95% = 0.16; Up95% = 0.24
20N-40N for 1945-2008:
Trend = 0.08; Adj R^2 = 0.23; p = 0.000; Low95% = 0.05; Up95% = 0.12
20S-40S for 1945-2008:
Trend = 0.43; Adj R^2 = 0.82; p = 0.000; Low95% = 0.37; Up95% = 0.48
40N-60N for 1945-2008:
Trend = -0.09; Adj R^2 = 0.13; p = 0.002; Low95% = -0.15; Up95% = -0.03
60N-80N for 1945-2008:
Trend = -0.24; Adj R^2 = 0.08; p = 0.015; Low95% = -0.43; Up95% = -0.05