In 2006, Willis Eschenbach digitized Hansen A,B and C scenarios to 2005 (see here ). I used these values together with my own visual digitization extension to 2010 in my recent post. Subsequently Lucia drew my attention to a digital version of the NASA data placed online at realclimate here , referenced in a realclimate post here.
I carried out a routine comparison of the two versions. The realclimate version of Hansen Scenario C was 0.166 deg C warmer than Willis’ digitized version. In reviewing the data, realclimate Scenario C was higher than realclimate Scenario B, so an error has been introduced somewhere in the process.
Which raises the question: how did this error get introduced
into the NASA data published digitally for the first time at realclimate? Did it get introduced in digital copying? Or did NASA itself digitize the Hansen scenarios from print media and introduce the error then? In fact, exactly what is the provenance of the digital version presently archived at realclimate? Gavin did not say in his post. Did Gavin digitize the print media? Did someone else digitize it? Or is it digital data? [Update: these matters have been resolved]
Steve: For some reason, the 1994 value of Scenario C is lower than the 1994 value of Scenario B in the original graphic, notwithstanding the lower forcing of C versus B.
It appears that Willis’ digitization is from a later and muddier version of the graphic and is incorrect at a few points though the average difference is not material. This leaves the question of why C is higher than B in 1994.
Update Jan 21: Willis digitized an image from 1999. Gavin said in an RC comment on Dec 22, 2007 (but not in the note itself) that the scenario data was digitized (presumably from the Hansen et al 1988 graphic). However,as far as I can presently determine, the other data sets e.g. radiative forcing in wm-2, also archived by Gavin, does not correspond to a Hansen et al 1988 graphic and therefore could not be digitized from a Hansen et al 1988 figure. Maybe it’s a digitization from another publication or maybe it was calculated; hard to say at present. I’ll email Schmidt and ask him.