Sunday, December 13, 2015

Cop out or tipping point?

Jim Hansen isn't right about everything these days - this paper has rightly had a rough ride (ignoring the delusional nonsense) and I wait with interest to see what transpires. But on the Paris talks, he's pretty much right. He's worth quoting in full (as reported in the Guardian and elsewhere):

It’s a fraud really, a fake. It’s just bullshit for them to say: “We’ll have a 2C warming target and then try to do a little better every five years.” It’s just worthless words. There is no action, just promises. As long as fossil fuels appear to be the cheapest fuels out there, they will continue to be burned.
James Hansen, Columbia University

It is also interesting to see that, just as most scientists have regretfully given up on 2C as a plausible target (maybe we could still just about do it in theory, but we certainly won't without lots of serious and immediate effort), the politicians decide they will aim at 1.5C instead. I predict a lot of Canute analogies and cartoons as the temperature continues to rise steadily.

On the other hand, it could be seen as a positive sign that at least the politicians are talking seriously about the need to cut carbon emissions, even if it is merely talk. It's not beyond the bounds of possibility that at least some nations might act in accordance with their words and put their money where their mouths are. If we really did achieve carbon neutrality before the end of the century, I'd regard that as a pretty positive outcome. But it's a long way off from here. Of course a carbon tax/fee/whatever as espoused by just about everyone who's thought about the problem and who does not have a vested interest in it would be the obvious starting point, and what matters from here is the start rather than the endpoint. What does everyone else think?

Friday, December 11, 2015

The benefits of an informed prior

Since Bayesian priors seem to have come up on a couple of blogs recently...

A few weeks ago I got a rather spammy email about a “climate change challenge” from someone I'd not come across before. Looking at his “publication list”, that is perhaps not so surprising (the most recent ACP submission listed there was rejected without review, so cannot be found on their web site). Anyway, it's just a typical kooky site full of claims about how everyone else is wrong apart from the author who cannot get his groundbreaking theories published, move along nothing to see etc...

Shortly afterwards, Doug Keenan announced a “contest” wherein all and sundry were challenged to identify from a large set of random time series which of them had been generated by a trendless random process, and which were generated by one with a known trend. Of course the trivial trick underlying his game is to make the trend small relative to the inherent variability of the random time series. For a simple example, consider if I generate a set A consisting of 500 samples from N(0,1) and a set B of 500 samples from N(1,1). If I publish the 1000 values, no-one could possibly hope to identify correctly which were from A and which were from B, because any value like 0.3 or 0.8 could easily have come from either set. If I'd used N(0,0.1) and N(1,0.1) for the two sets, on the other hand, it would have been rather different...

Amusingly, “I'm a genius time series analyst” Keenan bungled his calculations, as is documented in the comments here. His original set of trendless and trended series were sufficiently well separated that a successful partitioning might have been possible, at least with a bit of luck. Of course, his “$100,000” prize was “based on the honor system” so any entrant's chance of collecting would have to factor in their opinion of how honourable he is. I suggest that his juxtaposition of “My name would be mud if I reneged”, with the fact that he actually has reneged on his challenge by withdrawing the original set of samples and replacing it with another, might be usefully considered as evidence on the matter.

As for the Bayesian prior, that's what got me to the same answer as Andrew Gelman without the need to do all the calculations...

Wednesday, December 09, 2015

As I was saying....

So someone asked Andrew Gelman about Nic Lewis' work on climate sensitivity. And he replied:

“Despite what the Wikipedia entry says, there’s no objective prior or subjective prior, nor is there any reason to think the Jeffreys prior is a good idea in any particular example. A prior distribution, like a data distribution, is a model of the world. It encodes information and must be taken as such. Inferences can be sensitive to the prior distribution, just as they can be sensitive to the data model. That’s just life (and science): we’re always trying to learn what we can from our data.”

Which, enouragingly, is pretty much what I have been saying to Nic over a long period of time, both in person and perhaps once or twice as a reviewer of manuscripts. I am, however, not optimistic that the message will ever get through to him, as he seems completely impervious. But perhaps the rest of us can just carry on with life regardless.

Edit: having just had another glance at ATTP's post, and the still-growing comment thread, I see no reason to change my opinion about the message getting through... 

Monday, December 07, 2015

[jules pics] Getting wet

Gavin sent me a nice message yesterday with the curious title, "Stay Dry". Then I remembered that he is an American these days and one should not take these things literally. I interpreted it as a version of that "Stay Safe" phrase they love to use. Naturally it is not possible to literally Stay Dry in Yorkshire. It is always raining outside, and inside the new houses leak because they are new, and the old ones leak because they are old. However, recently, it has been quite a bit wetter than is normal! Even wetter than normal wet flood weather!! Apparently the water has invaded the homes of more than 5000 people in this part of the country, and the town where I went to ("high") school is now a Zombie Apocalypse. To be honest it never has been that cheery a place... 

I'm not one for disaster photography. Today the sun came out for a moment, so I cycled up to the local waterfall, Scaleber Force, which was in great form.


I suppose I missed the best one - apparently, for the first time evs, the waterfall has started flowing over Malham Cove. That's just a few miles away from Scaleber, on the other side of the watershed.

Meanwhile, James is practising his lime mortaring on some of the places where leaks sprung in our house. We avoided buying one of the newish houses nearby that, although favourably priced, seemed to me to be rather close to the flood plain. Ours is over 100 years old, but that alone doesn't offer much in the way of guarantees for dry toes if we are to have frequent 100 year events. 

Posted By Blogger from jules' pics.

Sunday, December 06, 2015

[jules pics] Sand Dunes #2

This one has been the front page picture on my iPad ever since...

The next morning, James and I climbed the nearest dune peak.
The wind had done a good job of smoothing out all the footprints of the day before, and ours were the first footsteps of the day.

Back to the lodge for a traditional US-stylee breakfast (pancakes etc), and we were back in Boulder that afternoon.

Posted By Blogger from jules' pics.

Wednesday, December 02, 2015

Trivial pursuits

So for some reason I got invited to participate in the latest Bray and von Storch survey of climate scientists, having not (IIRC) been asked previously. I barely got started on the meat of it before giving up. Screeds of hopelessly vague multi-choice questions with no context, like: how well do you think climate models can deal with clouds (answer from "very adequate" to "very inadequate"). Can or do deal with? Adequate for what? I'm not impressed.

More interestingly, I swapped a couple of emails with the author of this article over the past couple of weeks while he was writing it. Seems that I didn't say anything quotable enough to get quoted in it, but it looks pretty good to me.

Edit: Oops, first time round I was focussing on the quotable quotes to see if I disagreed with them. On a more careful re-read the author seems to think the last glacial maximum was only 1C colder than the present. No, it was 4C colder (than pre-industrial, ie 5C colder than now).