Wednesday, September 14, 2005

A betting update

There are no new bets to report, but there has been some behind-the-scenes effort in trying to set them up.

Most of the chasing has been done by William Connolley and Brian Schmidt. In the aftermath of my bet being announced, various pundits boldly claimed that they would be willing to take the "cold" side of a bet on the same terms or similar. Chris Randles quickly took one of them on for 500 pounds, which I reported here. However, subsequent attempts to chase down the others have so far proved fruitless.

Brian Schmidt tried here, with no response so far.

William Connolley has tried to get something out of "I'm happy to bet loads of money" Piers Corbyn, but nothing's been arranged yet. He's also emailed Tim Haab and I wait to see what, if anything, transpires.

Lubos Motl made a rather childish offer that he would accept odds of 8:1 in his favour on a 10 year bet, but only so long as it used only a single year of data at each end. Of course, this makes the temperature change very noisy due to interannual variability, as you can see on the graph below:
Here I've plotted the NASA GISTEMP annual temperature anomalies, and a 5-year smoothed version (both offset by 1C). The decadal temperature changes are shown below that, with the zero line indicated. As you can see, there have been two occasions in recent decades (three if you go back as far as 1976-1966) when the 10-year change has been briefly negative even during a period which has seen strong warming. William Connolley gets a similar result using a different data set. So Motl's 8:1 offer is roughly a fair bet even under conditions of continued strong warming - hardly a sceptical viewpoint. With a 5-year smoothing filter, the cooling peaks are eliminated, but he wasn't prepared to negotiate on such a bet.

An analytical look at the data gives a similar result. The annual temperatures have a variability of about 0.09C about the trend, which means that a straight decadal difference has a variability of 1.41*0.09C = 0.13C. The trend itself is about 0.17C, which implies that under the assumption of continued warming, the overall decadal temperature change is (roughly) a sample from the Gaussian distribution N(0.17,0.13) which has a 10% chance of being negative. Smoothing substantially reduces the variability - under the (perhaps slightly questionable) assumption that the temperature anomalies of consecutive years are independent, the distribution would be close to N(0.17,0.06) which has less than 1% chance of being negative.

So, no new bets yet. But both Brian and William have now offered significantly better odds than I had to, in the hope that this might tempt some of the sceptics who merely claim that future temperature change is no more likely to be up than down, as opposed to my opponents (and Piers Corbyn) who confidently predicted that cooling was imminent. William has offered 7:3 for an unsmoothed decadal difference. Brian has offered 2:1 on decadal bet, and 3:1 over 20 years. Until and unless they find any opponents, it seems reasonable to conclude that whatever the market rate is, it is higher than those offers on the table.

12 comments:

Bananus said...

Hello,

a small question has arisen here and I want to know if you have the answer. I saw that the GISS temp dataset ( http://data.giss.nasa.gov/gistemp/tabledata/GLB.Ts.txt ) has changed most of its temperatures a little bit (up to 0,10°C) somewhere between June and now. Do you have an idea why?

James Annan said...

Good question...I don't know for gistemp specifically, but I do remember reading something about the CRU data set on this subject...

Ah, here we are. At the bottom of that page, they say that recent historic temperatures get updated with late arrivals of data for up to 2 years, and their data processing can affect temperatures for up to 4 years. At least the first of these reasons is likely to apply to gistemp too.

In fact, I've just checked and the file I downloaded a few months ago (data to April 2005) differs from the current version as far back as 1985! But the differences are only the odd 100th of a degree here and there. Maybe someone recalibrated a few data sets or added in some new ones.

Incidentally, I've been using the combined land-ocean version here rather than land-only which you refer to.

Lumo said...

I've made a childish offer because I know that most of the global warming advocates have completely childish ideas about statistics. Let me admit that it's not your case.

Chris. F. Masse said...

Hi,

James Annan, please express the odds as percents.

Best regards,

Chris. F. Masse
http://www.chrisfmasse.com/2/prediction_markets/

James Annan said...

Well Lubos,

Why not make a serious offer? Do you expect continued warming as the IPCC TAR predicted?

Chris,

That's a good idea. All this 2:1, 1:2 etc is a bit tedious. I will try to do so in future. But the mental arithmetic is probably good for my reader(s?).

John Finn said...

Interesting topic.

I reckon Lubos' 8/1 is a bit high but not by much. The reasons being

1. There is '"at least 0.5 deg C warming in the pipeline" according to James Hansen and Gavin Schmidt - the bulk of which should be evident in the near future.

2. Models project a 3 degree C increase over the coming century which is 0.3 deg C per decade
not 0.17 deg C per decade which is the current rate of warming.

3. Betting odds need to reflect "the consensus". If James Annan is from the UK he may be aware that England's odds to win the world cup are much shorter than the likelihood that they will actually win it. This is the odds are based on the number of people who will actually bet on them (.i.e a lot of people in England will bet on England) I recently bet on Northern Ireland to beat England @ 14/1 - and won. I would not have placed the bet at 2/1, for example.

Depending on the actual bet and the timescale, Cooling should carry odds of somewhere between 4/1 and 13/2. Anything lower is a poor value bet.

In a nutshell, most sceptics believe cooling is as likely as warming (over the long term), but as with other ‘investments’ such as shares there's no point in going "against the crowd" for a low return.

Steve Bloom said...

John, this isn't betting on horses. The point is not to make money, but to see if people are willing to put their money where their mouth in terms of what they really think is likely to happen to climate. Tilting the odds based on available bettors makes no sense. Now we will see if Lubos has the guts to make an even odds bet or if he's just blowing hot air. I suspect the latter.

James Annan said...

Yes John,

IF you accept the standard scientific analysis, then Lubos' bet is roughly fair. That's the whole point. If he thinks the standard scientific analysis is wrong, then he should be able to offer odds that are attractive both to himself and to me. He refuses to do so. Your "low return" argument is nonsense, because the money does not have to be paid up-front (and it if was, it could be sensibly invested anyway, so the betting return is additional to any investment opportunities)

Estimates of ~3C warming over 100 years depend on strongly increasing emissions, and in this case, the warming will accelerate greatly over the second half of the century. Attempting to equate this long-term forecast with 0.3C over the next decade is a standard septic misdirection. The IPCC TAR explicitly estimates a likely 0.1-0.2C per decade for the near future, and that will happen pretty much whatever we do (within reason).

John Finn said...

James

Your bet is not based on standard scientific analysis, but on past observations. The standard scientific analysis suggests accelerating warming. You win - even if the trend 'slows'.

If James Hansen and Gavin are right there is a 0.6 deg C warming which is going to happen even if GHG levels remain fixed. See here

http://www.realclimate.org/index.php?p=148#more-148

Furthermore Gavin refers to a Wigley paper in this article. Wigley clearly indicates that the bulk of any warming will be 'up front' though there is a long tail.

Any talk by the IPCC that warming will be gradual at first then accelerate is bull. The forcing response to increasing CO2 is logarithmic.

The consensus is also important. In fact as far as I'm concerned it's everything. I regularly bet (and win) "against the crowd" because the expected returns are so good.

You say "you can invest the money first - then pay up". Well thanks for that, James, but you can do that with any bet.

For what it's worth I think you are a slight favourite with the Russian bet - but NOT with an increasing trend.

James Annan said...

So John, if I'm only a "slight favourite" for my evens bet, then surely the 2:1 - 3:1 offers on the table should be plenty to tempt you.

There's no point bothering to explain the science to someone who is just going to duck and weave. So I'll simply ask you if you can propose a bet that are prepared to make, which you believe significantly disagrees with the scientific consensus. If you can't do that, please stop wasting my time.

EliRabett said...

You know, even though he knows slightly less than squat about climate, Lubos has a point. At some level, even the Motl's and Singers of the world know that they are slinging bull. They are quite happy to take lunch at the Marshall Institute, but they are not going to risk a dime. You guys are looking in the wrong place. Try some of the US right wing sites, like Free Republic or Little Green Footballs.

Brian said...

Eli, I tried to post the bet at Free Republic, and they deleted my comment banned me:

http://backseatdriving.blogspot.com/2005_06_01_backseatdriving_archive.html#111992290974122050

And LGF is less democratic than they seem (surprised?). They've closed their comments to new commenters, just letting the old hacks in, along with (I assume) people they like.