Understanding Climate Risk

Science, policy and decision-making

Shifts, jerks or figments? You be the judge

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First week of December I was at the American Geophysical Union Fall Meeting in San Francisco. This meeting is big: an estimated 20,000 attendees this year dealing with all matters geophysical from global change to stressed rocks. I had a poster to give, and being super organised, spent the first two days of the meeting preparing it. The AGU’s 24 hour poster print service got me a big 6’ x 4’ poster by the Thursday session.

And it was a complicated poster, let me say, though there were simple bits in it. When you want to overturn a paradigm, a simple “it ain’t so because it ain’t” doesn’t cut it. The main thesis is that the signal-to-noise model, which assumes a smooth anthropogenic change signal within a background of noisy natural variability, is wrong. Instead the climate follows a deterministic non-periodic pathway, to coin Ed Lorenz of butterfly complexity, where the forcing produced by increasing greenhouse gases does not gradually change climate, but comes in steps. The bulk of the energy is stored in the ocean, with climate showing little warming, only to be released in periodic bursts influenced by the processes associated with climate variability.

This is important, because it suggests that all the work going into calculating probabilities of mean change using climate model ensembles, has limited utility. If the climate shifts in a series of step changes, then this is more important than calculating a probability density for a series of curves for a given date.

So I was standing next to the poster waiting to ambush the unwary, met Jess of LP commenting fame, when along hopped Eli the Bunny. After checking overhead to see that Ethon wouldn’t eat my liver if I ambushed the bunny, I blew his cover. Happily, Eli was intrigued enough by my bravado in challenging the accepted wisdom of how climate is changing, he agreed to do a post when the paper setting the groundwork became available. Which it did, the week before Christmas (another job I got done while at the conference).

He’s called the steps jerks. Which is an eye-catching headline and gets people looking for insults. The jerks are happening because the system is buffered as long as the upper ocean absorbs the energy from climate forcing. Until it has to do some work and the energy can go in two directions: into the atmosphere or into the deep ocean. I don’t have the exact mechanism figured out yet, but am working on it.

You can join the discussion at Rabett Run, comment here, have a look at the poster and the paper, which covers the basic methodology and how it has affected the climate in south-eastern Australia. I’ll add some of the more straightforward stuff from the poster in the next few days.

 

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Written by Roger Jones

January 4, 2012 at 12:36 am

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