DeLong update

by Russ Roberts on February 21, 2010

in Environment

Brad has revised his post. I have been upgraded from “liar” to “gullible” for believing the Daily Mail article. I will let readers decide for themselves whether this charge is accurate.

The bottom line on the facts is that according to Phil Jones, for the last 15 years, there has been a warming trend of .012 C per year, a trend that is not statistically significant. Whether 15 years is a short time is something of a judgment call. That may turn out to be irrelevant in either direction as time passes. This trend is below the average trend for the last 35 years which is .016. That is a big difference (25%) but even that difference may not be statistically significant. I don’t know. There has been a cooling trend of .012 over the last seven (I think) years. Seven years is a short time but it is food for thoughts. For any of these comparisons you’d want to know the changes in the underlying variables–the natural and man-made carbon sources over the periods to know what to make of it. The same is true of any comparisons to the 1860-1880 period which evidently¬† saw warming of .016C per year.

I remain agnostic on AGW. I am not a climate scientist. But I know something about multiple regression analyses with complex phenomena. It is my impression that like macro models, these models do not perform well with out-of-sample predictions. That is, they are fitted to the past and then used to make predictions about the future. When the future does not turn out to be like the past predicted, the models are tweaked (improved!). The problem with this methodology is that the tweakers of the models are prone to confirmation bias. See my post here, Arnold Kling here or the work of Ed Leamer.

I have closed comments on the¬† post where I defended myself. I had said I would delete ad hominem attacks on Brad. I’ve been away from my computer for the last 36 hours. There are now 261 comments, many of which contain ad hominem attacks. It’s too costly to weed all those out so I will let them stand but I am closing the post to further comments.

This post is closed to comments. While I appreciate the support and praise, it embarrasses me to see this site used as a vehicle for screaming at other people. If you want to say something in response to this food fight, just send it to me privately, please.

A couple of thoughts on Brad. He is welcome to be a guest on EconTalk any time. I would be particularly interested in interviewing him on Keynesian economics and the stimulus. I have invited him in the past more than once. He has politely declined each time. I’m sure we could have a civil conversation.

While Brad the blogger is not one of my favorite people to read, I have often benefited from reading Brad the economist. As Future of Capitalism points out, I praise one of Brad’s papers in my latest book.

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