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Friday, November 15, 2013

Salby's Ratio in Hamburg

Just over a year ago, I drew attention to Murry Salby's efforts to suggest that CO2 was not a major contributor to ongoing warming in the twentieth century by the simple expedient of changing the scale ratio between two graphs that compared CO2 concentrations and temperature.  By greatly reducing the number of parts per million of CO2 in the scale relative to the degrees centigrade when comparing observations, Salby drastically increases the apparent slope of the CO2 observations relative to the temperature observations, thereby artificially creating an appearance of disparity where none exists.

I recently noticed the same two charts were used by Salby in his lecture at Hamburg.  Not only were the same two charts used, but much of the discussion was the same.  First he draws attention to the close match between CO2 concentrations and temperatures in model projections of the twenty first century, telling us that:
"Global temperature doesn't just increase with increasing CO2 - it tracks it, almost perfectly."

As in Sydney, having overstated the close relationship between temperature increases and CO2 increases in the model world, Salby goes to great lengths to draw attention to the disparity between the observed rise in CO2 and that in temperature - a disparity almost entirely created by his manipulation of scale ratios.  He says (1:02:00):
"In blue is the observed record of global temperature from the satellite MSU.  In green the observed record of CO2.  The long term evolution of temperature parallels that of CO2 during the 1980s.  It's been scaled to match the trend then, as was obtained by models of the IPCC.  With account of the eruption of Mount Pinatubo in 1992, their correspondence is similar during the 1990s.  But after the El Nino of 1997, CO2 continued to increase.  Global temperature did not.  Their divergence over the last decade and a half is now unequivocal."
(My emphasis) 
As can be seen by comparing with the transcript of his Sydney Institute lecture from a year ago (in my article linked above), that is almost word for word.  The only significant difference lies in the addition of the sentence which I have bolded; a sentence which purports to explain the choice of scale ratio.  That sentence is rather ambiguous.  It is not clear what Salby mean by it, and he nowhere specifies the method whereby he "scaled to match the trend".  More importantly, there is no interpretation of that sentence in which it is both relevant and true.