Climate scientist John Christy has responded to the blog attack yesterday (7 May 2016) from fellow climate scientist Gavin Schmidt.
Christy, from the University of Alabama in Huntsville, was accused by Schmidt, who is director of NASA’s Goddard Institute for Space Studies, of giving “misleading” testimony to the US Congress earlier this year.
Christy told reportingclimatescience.com in an email that it has been “thoroughly demonstrated that Schmidt (again) was completely wrong”.
Schmidt’s post on the realclimate.org blog criticises the way Christy compares the performance of computer climate models in predicting future global temperatures with the temperature trend from historical observations by satellite. Christy presented a graphical comparison between model forecasts and satellite observations in testimony before the US House Committee on Science, Space and Technology on 16 February 2016 to support his contention that models exaggerate the forecast rate of future warming.
Schmidt states in his blog that the graphs Christy presented to the committee are misleading because of the choice of baseline, the use inconsistent data smoothing and the treatment of data and model uncertainties. Schmidt presents his own graphs that show that the satellite observations are, according to his analysis, within the range forecast by models.
Christy counters that “both the reference period and the alleged error analysis that I did were appropriate”. He points to an analysis by climate statistician Steve McIntyre on the ClimateAudit.org blog as supporting his case. Christy added that “when Schmidt’s “sleight of hand” is considered, his analysis SUPPORTS my results” – a reference to Schmidt’s choice of baseline and data for the comparison which has the effect of minimising the difference between observations and models.
The row over the use of these graphs erupted in public in April on Twitter when Schmidt criticised another climate scientist, Judith Curry from the Georgia Institute Of Technology, for planning to use Christy’s graphs in a presentation. Schmidt’s decision to publish his blog piece yesterday re-ignites this bitter dispute.
This argument is between two professional climate scientists who have sharply differing views on the issue of climate change. Schmidt is a forceful advocate of the case for human driven climate change and Christy is an acknowledged sceptic.
But, despite the personalities and the climate politics, a number of important scientific issues relating to climate change lie at the heart of this exchange, including: the reliability of climate models; the rate of global warming; and the sensitivity of the climate to increasing levels of greenhouse gases. Bluntly, if Christy is right then climate model forecasts are exaggerating the degree of future climate change leading to unnecessary and expensive mitigation policies being enacted by governments around the world; but if Schmidt is right, then the observations do in fact confirm the predictions of climate model forecasts and the risks of future climate change are all too real.
Gavin Schmidt’s blog on realclimate.org
John Christy’s presentation to the US House Committee on Science, Space and Technology.