No. of Recommendations: 7
I'd like to draw the board's attention to a new-this-year blog which I thoroughly recommend for the clarity and elegance of its discussion of 'FAQs'-

It's mission statement is seemingly modest -

I'll be trying what seems to be an unusual approach in blogs -- writing to be inclusive of students in middle school and jr. high, as well as teachers and parents (whether for their own information or to help their children)

- but I think that suggests an underestimation of its potential (or maybe, heck, that's about my level! ;-)). For example, here is an excellently written extension of the dice analogy (which Hansen uses), one which surely will explain better than I can the distinction between climate trend and natural variability:

....use 5 dice (again 6 sided). In this case our 'climate' is a total of 17.5, which still doesn't happen as weather, although you can get close. The maximum is 30, and the minimum is 5. The maximum difference from climatology is 12.5. But most of the time we'll be close to climatology. Take 5 dice, throw them, add them up and record the result for a couple hundred throws....

Within your 200 totals, you'll find some runs of constantly increasing values, and about as many runs of constantly decreasing values. Some of the runs will be long, and some short. But the number of each is about the same whether it's increasing or decreasing. If you compute the average of the first 5 sums, then 10 sums, ... out to the whole 200, you'll see that the average wobbles around. It tends to be closer to 17.5 as time goes on (as you average more tosses) but only in a very jerky fashion.

Suppose I take one of your dice and tape a 6 over the side that should read 1. The average throw now totals 18.3333 (repeating), instead of 17.5. The minimum is now 6 instead of 5, but the maximum is unchanged. What will happen, though, is we'll see the high totals more often. Each of these is more or less a fair description of what we've seen in the climate of the last 120 years -- warmer minimum temperatures, higher averages, and not much change in maximum temperatures. (Not a perfect analog, but pretty good for only 5 dice.)

...How many throws do you need to make before you can tell that there are fewer low numbers? More high numbers?

In doing climate change detection professionally, these sorts of analyses are applied. Are there more extreme highs? Fewer extreme lows? Higher average? Just how many data points do we need to detect that in the statistics?

Final question: when did the climate change? When you have a long enough series of throws to detect it in the statistics reliably, or when you saw me tape over the 1 face with a 6?

Simple, eh? But the fact is, the concept is simple! It's surely easy for any reasonable person to see why the range of 'natural variability' (6 to 30 in the altered case) is bound to far exceed the extent of the trend, even over a long period of throws. Isn't it?

This blog is written by a scientist who is active in the relevant field and who, evidently, is persuaded that AGW is a concern. I guess that means he is an 'alarmist' to those who insist on using terms they intend to be derogatory towards those with whom they disagree. For anyone else, whatever your persuasion, I recommend the blog for clear explanations of what such a person thinks (I read 'Wattsupwiththat' to find out what the 'other side' is thinking, so I don't think there's anything one-sided in my suggestion!).

Here's a bit more to finish with, dealing with a topic that has been done to death here and elsewhere:

Remember what happened when you tried my climate change detection experiment. Even with random numbers, you got runs of several consecutive 'years' of warming or cooling. Free variability does this to you. So if you're looking for trends or other systematic things, you need to look at a long enough period that the free variability can't lead you to a mistaken conclusion. Plus, of course, you have to make that allowance for all the things that you know happen and affect the variable (global mean temperature) you're interested in but are due to processes (solar variability, El Nino, volcanoes, ...) that you're not concerned about at the moment.....

- and it goes on to talk about the obvious distortions of cherry-picking (this entry comes up from my first link).

I think I might be quoting from here a lot - should save me some typing!
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