In a prior post, “GISTEMP: 1200km vs 250km Smoothing Radius Comparison”, I examined the difference between the 1200 and 250 km radius smoothing in GISS Global Temperature Anomaly data over the term of January 1978 to April 2008. The intent was to determine the impact of the 1200km radius smoothing used by GISS in their global temperature anomaly data.
In it I described the process I used to retrieve the two sets of data. I employed the same methods for the annual long-term data used in this post.
This post examines the effect of the 1200km radius smoothing on the long-term global temperature data, using annual data from 1880 to 2007.
GISTEMP – 250km VS 1200km SMOOTHING
Figure 1 illustrates the raw GISS global temperature anomaly data using 250km and 1200km radius smoothing. For the majority of the term, there is little apparent difference between the two curves, but this perception may be due to the scale of the graph. What stands out for me is the amplification of the 1200km curve after the 97/98 El Nino, but I look for that.
In Figure 2, the data has been smoothed with a 7-year running-average filter. Again, there appears to be little difference between the two data sets.
But when the difference (1200km radius smoothing minus 250km radius smoothing) is illustrated, Figure 3, the magnitude of the adjustments becomes clearer. Using the lowest (-0.07 deg C at 1888) and highest (0.1 deg C at 2007) values as reference, the 1200km smoothing contributes 0.17 deg C to the warming over that period. Referring back to the 250km radius smoothed data in Figure 1, the difference between the minimum (-0.33 deg C at 1890) and maximum (0.53 at 1998 and 2005) GISS global temperature anomalies is only 0.86 deg C. Using these two extremes, the GISS 1200km radius smoothing contributed more than 20% to the maximum global temperature rise illustrated.