Christy: Schmidt Is “Completely Wrong”

A tale of two graphs. Both graphs compare the record of computer climate model forecasts of global warming with historical observations of global temperature change. Christy's graph (on the left) was branded as "misleading" by Schmidt and Schmidt (whose own version of the graph is on the right) has been called "completely wrong" by Christy. Courtesy: John Christy and Gavin Schmidt.A tale of two graphs. Both graphs compare the record of computer climate model forecasts of global warming with historical observations of global temperature change. Christy's graph (on the left) was branded as "misleading" by Schmidt and Schmidt (whose own version of the graph is on the right) has been called "completely wrong" by Christy. Courtesy: John Christy and Gavin Schmidt.

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.

Appropriate

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.

Sources

Gavin Schmidt’s blog on realclimate.org

John Christy’s presentation to the US House Committee on Science, Space and Technology.

Steve McIntyre’s ClimateAudit.org posts here and here.

See also

Schmidt Blasts Christy For “Misleading” Congress

5 Comments on "Christy: Schmidt Is “Completely Wrong”"

  1. Christy is correct!

    In plain English: If you want to compare trends between model predictions and observations over a fixed period of time, you do so from the beginning of that fixed period, not at some later data weighted point in time.

  2. Christy and his cohort Roy Spencer continue to defend an “analysis” that is deeply flawed. Citing McIntyre as backing him up isn’t really credible, because McIntyre could not be considered an unbiased resource.

    Here’s something I wrote about it, emphasizing from a different source all that is wrong with what Christy and Spencer have been pushing.

    http://tugpullpushstop.blogspot.com/2013/06/on-roy-spencer-and-his-model-post.html

    And here’s a quote from the source I quote in the article (much more at length in the article):

    “What I’m trying to say is that the variance and mean of the “ensemble” of models is completely meaningless, statistically because the inputs do not possess the most basic properties required for a meaningful interpretation.”

  3. John Shade | May 9, 2016 at 9:35 am | Reply

    Schmidt’s tweeted rudeness to Curry was unbecoming, and the subsequent analyses more calmly presented by McIntyre and Christy reveal just how thin the ice was upon which he chose so unwisely to venture. Was it on the spur of the moment, or had he been seething for a while over Christy’s (in my opinion excellent) presentation to Congress? It should be troubling to the political and scientific establishments to see how often the promoters of alarm over CO2 have been demonstrated to be sadly lacking in statistical skills. See ‘The Hockey Stick Illusion’ book for a gripping read on one of the more highly visible blunders.

  4. Dan Aldridge | May 9, 2016 at 8:57 am | Reply

    Um, Christy represents the opinion of a tiny handful of contrarians. Why is it that he and the rest of that group (I can count them on one hand) are always the ones giving “presentations” to Congress?

    • Because ALL sides in science should be heard, not just the “popular” ones or it verifies that science is not what this is about. As I recall, Congress listened to Merril Streep on alar, all kinds of “anti-vax” advocates, etc. Listening to all sides is the proper way to make a decision, not go with the popular vote. Unfortunately, sometimes Congress goes with things that are wrong, such as alar and the actress that pushed banning it, for whatever reason. Congress can be wrong just like everyone else and the majority view can be wrong, both in politics and science.

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