Significance doing the rounds

I'd like to commend to readers a couple of postings on the subject of statistical significance in the temperature records.

Last week a little visited website called Real Climate had an article by climatologist Stefan Rahmstorf, which addressed many of the issues discussed here in recent months. What I found interesting was that there was a measure of agreement:

...the confidence intervals (and claims of statistical significance) do not tell us whether a real warming has taken place, rather they tell us whether the warming that has taken place is outside of what might have happened by chance.

Click to read more ...

Pierrehumbert and unrealistic expectations

David Appell has written a rather strange article, purportedly about climate sensitivity, but actually about individual components of the climate system. It's only at the end that the climate sensitivity question is addressed:

“There’s really nothing in [the recent temperature record] that changes our estimates of climate sensitivity.” Calculation of that all-important number from the 20th century record is not possible, because the aerosol forcing is not well known, nor are the data for ocean warming up to the task.

“Any estimate of sensitivity requires all of the record and not just the last 20 years of it,” Pierrehumbert says. “The smaller the piece of it you take, the less certainty you have in your result.”

Nonetheless, he agrees that earlier warming may have been deceiving.

“I think it’s true that some rather sloppy discussion of the rapid warming from the 20th century has given people unrealistic expectations about the future course of warming.”

This is rather odd, because the IPCC publishes estimates of aerosol forcing. They may be uncertain, but they are hardly unknown. It's also rather odd that flat temperatures don't, in Pierrehumbert's opinion, change estimates of climate sensitivity. I'm sure someone (Ed Hawkins perhaps, or was it James Annan?) said that flat temperatures could do nothing except reduce the value.

Moreover, I also recall that Forster and Gregory reported that aerosol forcing affected the uncertainty of their estimate of climate sensitivity but not the value. I think I am also right in saying that their method is unaffected by ocean heat uptake uncertainty.

That said, the unrealistic expectations of the future engendered by sloppy discussion of 20th century warming need to be more widely recognised, so it's good to see the case being made by an RC insider.

RealClimate on Yamal

Gavin Schmidt has issued the official response to the recent excitement over Yamal. I have to say, even on a brief glance through it is a wild piece of writing.

Briffa, as we know, reprocessed data from Hantemirov and Shiyatov in his 2000 paper on Yamal. He used the same data again in his 2008 paper on regional chronologies. Schmidt says:

McIntyre is accusing Briffa of ‘deception’ in stating that he did not ‘consider’ doing a larger more regional reconstruction at that time. However, it is clear from the 2000 paper that the point was to show hemispheric coherence across multiple tree ring records, not to create regional chronologies. Nothing was being ‘deceptively’ hidden and the Yamal curve is only a small part of the paper in any case.

Click to read more ...

IPCC Circus - Josh 107

Some context. Over at Keith Kloor's Ray Pierrehumbert, RealClimate blog founder, left a rather rude comment ending with this about troublesome voices like McIntyre, McKittrick, and Watts.

"... big as the IPCC tent may be, I hope there will never be a place in it for any of these clowns."

Which made me conclude that Ray thinks that the IPCC is a circus and it should only be populated by approved and accredited clowns. Fair enough.

More cartoons by Josh

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Steig snippets

The reaction to Ryan O'Donnell's article about Steig has been astonishing, and the rate of deletion of comments from Real Climate hasn't been this high for...well...days.

Some interesting stories have emerged from all the noise:

"Threats"

A commenter called CAGW_99 left a comment at RealClimate noting that Steig could find himself called to testify before the House of Representatives.

Click to read more ...

Gloves come off

Ryan O'Donnell, who always seemed to be the icy cool leader of the team behind the rebuttal of the Steig et al Antarctic paper, shows that he can be pushed too far. His response to Steig's latest posting at Real Climate is a withering rebuke, the likes of which I don't think I have ever seen before.

It's up at Climate Audit and WUWT. Take your pick.

Josh 74

More cartoons by Josh here.

Josh 56

Fred on Foster and deFreitas

Fred Pearce in New Scientist looks at some recent developments in the ongoing battle between Tamino and the Hockey Team on the one side and sceptics deFreitas and McLean on the other. Judy Curry gets quoted.

WaPo on climate models

The Washington Post has an interesting article on climate models which features Gavin Schmidt making a robust defence of their usefulness:

Put in the conditions on Earth more than 20,000 years ago: they produce an Ice Age, NASA's Schmidt said. Put in the conditions from 1991, when a volcanic eruption filled the earth's atmosphere with a sun-shade of dust. The models produce cooling temperatures and shifts in wind patterns, Schmidt said, just like the real world did.

If the models are as flawed as critics say, Schmidt said, "You have to ask yourself, 'How come they work?' "

Now last time I heard, the models could get into an ice age but couldn't get out again, so I'm not sure whether Gavin is being entirely straight with us here. Perhaps the models have moved on though, although one could still wonder if they could move so quickly from not being able to get out of an ice age to being useful.