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Finally, Brad DeLong calls me a liar

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What took him so long? And not just any liar, the “lyingest economist alive.”

Details below the fold as well as my defense, if it interests you. It’s a bit long, but when you’re called the “lyingest economist alive” I think it’s worth a careful response.

Brad doesn’t like this pos [2]t where I wrote that Phil Jones, climate scientist, says there’s no warming trend over the last 15 years. I had read (and linked to) this article [3] from the Daily Mail that began:

The academic at the centre of the ‘Climategate’ affair, whose raw data is crucial to the theory of climate change, has admitted that he has trouble ‘keeping track’ of the information.

Colleagues say that the reason Professor Phil Jones has refused Freedom of Information requests is that he may have actually lost the relevant papers.

Professor Jones told the BBC yesterday there was truth in the observations of colleagues that he lacked organisational skills, that his office was swamped with piles of paper and that his record keeping is ‘not as good as it should be’.

The data is crucial to the famous ‘hockey stick graph’ used by climate change advocates to support the theory.

Professor Jones also conceded the possibility that the world was warmer in medieval times than now – suggesting global warming may not be a man-made phenomenon.

And he said that for the past 15 years there has been no ‘statistically significant’ warming.

How would you interpret that last sentence? Here is what I said:

Of course Phil Jones has said recently that there’s no trend for the last 15 years.

Brad writes [4]:

Russ Roberts knows as well as I do–as well as anybody who has taken even one semester of statistics does–that “no trend” does not mean the same thing as “no statistically significant trend,” that you are unlikely to find statistical significance when you restrict your attention to a short period because your statistical tests then lack power, and that everyone literate in statistics asked for their point estimate of the warming trend since 1975 would say that it is almost as much as the overall trend since 1860: 0.012C per year as compared to 0.015C per year.

Russ Roberts knows all this. But he hopes to trick some of his readers by hiding it.

Lyingest economist alive…

Brad is right that small samples have less explanatory power. Is 15 years too short a time to find statistically significant global warming? One way to answer the question is to look at other 15 year periods. And longer periods, of course, which Brad does, because he is looking at the BBC version of the Jones interview [5] which has more data. Had I read the BBC version, I also would have known that Jones thinks there is a warming trend rather than merely a trend that is not statistically significant. I should have said that Jones admits that “for the past 15 years there has been no ‘statistically significant’ warming.” My mistake. Dear readers, I did not mean to trick you.

(I refrain from mentioning that Brad knew that I had linked to the Daily Mail story rather than the BBC version. I’ll just assume he made an honest mistake.)

The BBC version of the interview has some more data. That explains why Brad mentions 1860 which at first bewildered me. Again, from the interview with Jones:

A – Do you agree that according to the global temperature record used by the IPCC, the rates of global warming from 1860-1880, 1910-1940 and 1975-1998 were identical?

An initial point to make is that in the responses to these questions I’ve assumed that when you talk about the global temperature record, you mean the record that combines the estimates from land regions with those from the marine regions of the world. CRU produces the land component, with the Met Office Hadley Centre producing the marine component.

Temperature data for the period 1860-1880 are more uncertain, because of sparser coverage, than for later periods in the 20th Century. The 1860-1880 period is also only 21 years in length. As for the two periods 1910-40 and 1975-1998 the warming rates are not statistically significantly different (see numbers below).

I have also included the trend over the period 1975 to 2009, which has a very similar trend to the period 1975-1998.

So, in answer to the question, the warming rates for all 4 periods are similar and not statistically significantly different from each other.

Here are the trends and significances for each period:

Period Length Trend
(Degrees C per decade)
Significance
1860-1880 21 0.163 Yes
1910-1940 31 0.15 Yes
1975-1998 24 0.166 Yes
1975-2009 35 0.161 Yes

B – Do you agree that from 1995 to the present there has been no statistically-significant global warming

Yes, but only just. I also calculated the trend for the period 1995 to 2009. This trend (0.12C per decade) is positive, but not significant at the 95% significance level. The positive trend is quite close to the significance level. Achieving statistical significance in scientific terms is much more likely for longer periods, and much less likely for shorter periods.

I am grateful to Brad for pointing me to this additional information. (UPDATE: Brad is using degrees per year rather than degrees per decade–thanks to reader Phil for the correction.)

So this says the earth was warming between 1860 and 1880 at the same rate it has between 1975 and 2009. Three things strike me about that.

One is that sure is an awkward result for the theory that global warming is man-made. How much more carbon do you think the global economy is pumping out today compared to 1870?

Two is that 1860-1880 is “only” 20 years. Who would think you could find statistical significance for such a short period?

Three is related to what Brad wrote:

everyone literate in statistics asked for their point estimate of the warming trend since 1975 would say that it is almost as much as the overall trend since 1860: 0.012C per year as compared to 0.015C per year.

I think Brad is confusing the 1975-2009 estimate with Jones’s estimate of the 1995-2009 period which is not in the table. I think what Brad meant to say is this:

everyone literate in statistics asked for their point estimate of the warming trend since 1995 would say that it is almost as much as the overall trend since 1860: 0.012C per year as compared to 0.015C per year.

I’m not sure where Brad got that 0.015 number in talking about the warming trend since 1860. But assuming it is accurate, 0.012 is not “almost as much” as 0.015. True, they are both small numbers. But 0.012 is actually 20% less than 0.015, something everyone literate in arithmetic knows. There is also the awkward problem that you’d think the theory would predict more warming in the modern period not less. Of course there could be natural phenomena offsetting that effect–the world is a complicated place.

WARNING TO COMMENTERS: Comments that call Brad a liar (or a moron or similar ad hominem attacks) or that mention that Brad deletes comments he doesn’t like, will be deleted. Please keep the conversation on a pleasant level.

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