Guest post by Bob Tisdale
A number of bloggers on the WattsUpWithThat thread “Tom Karl’s Senate Dog & Pony Show – it’s worse than we thought, again” noted the curious errors in the trend lines in Tom Karl’s presentation to Senate. The one that stood out for me was slide 21, presented here as Figure 1. It showed the global land surface temperature anomalies and linear trends for the new (Version 3) versus existing (Version 2) Global Historical Climatology Network (GHCN) dataset.
First Observation: The slide title states the data is monthly, but the data illustrated are annual averages. Figure 2 is a graph of monthly Global Land Surface Temperature anomalies presented by the NCDC from January 1900 to April 2010. Monthly global land surface temperature anomaly data should look like that, with lots of month-to-month variation.
Second, there are two linear trends listed on the Karl slide. Version 2 is noted to have a linear trend of 0.83 deg C/Century, while Version 3 is claimed to have a linear trend of 0.91 deg C/Century. But the trend lines are nearly identical and they present linear trends of approximately 0.75 deg C/Century, Figure 3. The trend lines are erroneous or the values listed for the trends are wrong.
Trend lines of 0.83 and 0.91 deg C/Century should be noticeably different, as shown in Figure 4.
And for reference, the NCDC’s Monthly Global Land Surface Temperature anomaly data, Figure 5, has a linear trend of 0.78 deg C/Century.
And the the NCDC’s Annual Global Land Surface Temperature anomaly data, Figure 6, has a linear trend of 0.77 deg C/Century.
Makes one wonder. If a simple comparison graph with linear trends is so error filled…
Tom Karl’s Powerpoint Presentation is available here:
A full-sized copy of Slide 21 is here:
The NCDC Land surface temperature anomaly data is available through the KNMI Climate Explorer: