An Exchange Between Judith Curry and Gavin Schmidt

[Jack Hays]

Scientists at work.

Controversy over comparing models with observations

Posted on April 5, 2016 | 54 comments
by Judith Curry
My draft talk elicited an interesting conversation on twitter, that deserves some wider discussion.
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". . . A whole host of interesting issues are raised in this exchange:

• How to communicate complex data to a non technical audience?
• How to best compare model predictions against observations?
• What is are the most reliable sources of such plots to use in public presentations?

I’ll start with the third question first. When selecting figures to use in presentations or testimony, I am looking for the most credible figures to use. I use figures from the most recent IPCC assessment where possible. A second choice is a figure from the published literature. However, in public presentations and testimony, they are looking for the most up-to-date analysis with the latest observations (which aren’t in peer reviewed publications owing to research-publication time lags). Hence I have often used Ed Hawkins’ update of figure 11.25 from the AR5 comparing model projections and surface observations (Ed was the author of fig 11.25).
With regards to John Christy’s figure, he is the author of one of the main observational data sets used in the comparison. I don’t now the source of the time series that having provided, but the observations in gavin’s figure vs Christy’s figure do not look similar in terms of time variation. I have no idea how to explain this. I have to say that I think John Christy’s figure is more reliable, although some additional thought could be given to how to define the beginning reference point to eliminate any spurious influence from El Nino or whatever. . ."

 

[Jack Hays]

Climate FAIL / Climate Models
[h=1]The Illusions Provided by Time-Series Graphs of Climate Model Ensembles and Model Spreads[/h] Guest Post by Bob Tisdale The post Controversy over comparing models with observations at Judith Curry’s Climate Etc. prompted this post. Judith’s post includes a Twitter exchange and a couple of model-data comparison graphs furnished by Dr. Gavin Schmidt, the director of the Goddard Institute of Space Studies. The one from Gavin for the global mid-troposphere…