I have calculated from scratch the global averaged temperature anomalies for the 73 proxies used by Marcott et al. in their recent Science paper. The method used is described in the previous post. It avoids any interpolation between measurements and is based on the same processing software that is used to derive Hadcrut4 anomalies from weather station data. Shown below is the result covering the last 1000 years averaged in 50-year bins. I am using the published dates. Re-dating is a separate issue discussed below.
There is no evidence of a recent uptick in this data. Previously I had noticed that much of the apparent upturn for the last 100 year bin was due to a single Proxy : TN05-17 situated in the Southern Ocean (Lat=-50, Lon=6). The blue dashed curve shows the 50 year resolution anomaly result after excluding this single proxy.
Figure 2 shows the anomaly data using the modified carbon dating (re-dating). This has been identified by Steve McIntyre and others as the main cause of the up-tick. However I think this is only part of the story.
The new dating suppresses the anomalies from 1600-1800. There is a single high point for the period 1900-1950. The much larger spike evident in the paper around 1940 (see also here) is in my opinion mainly due to the interpolation to a fixed 20 year interval. This generates more points than measurement data and is very sensitive to time-scale boundaries. I believe you should only ever use measured values and not generated values.
There is no convincing evidence of a recent upswing in global temperatures in either graph based on the published or on the modified dates. I therefore suspect that Marcott’s result is most likely an artefact due to their interpolation of the measurement data to a fixed 20 year timebase, which is then accentuated by a re-dating of the measurements.
updated 24/3 : include re-dating graph