12 August 2007

Decadal-scale forecasting

Here's more on the decadal forecasting scheme I posted earlier. I think that was the first one that came across the feed, and it not especially clearly written...It was very late, too

Anyway, Nature News has the best report I've seen so far (I have to wait to read the paper...we get Science a few weeks late in the library for whatever reason...). I really like the accompanying graphic, reproduced here. To my mind, the graphic alone raises all sorts of questions and thoughts. More on that below, on to the story

British researchers have substantially improved the performance of a global climate model by adding observations about the actual state of the ocean and atmosphere. The results are of seminal importance for those trying to produce reliable short-term 'climate forecasts' on global and regional scales, experts say.

The team, led by Doug Smith of the UK Met Office's Hadley Centre in Exeter, has developed a climate prediction system that is capable of including natural variability in the climate system — such as that arising from anomalies in ocean circulation or ocean heat content — into modelling carried out by a global climate model...

I would think that there is small (but finite) chance the model follows that consensus forecast path. I suppose it really depends on what the ocean does and how well the model reflects that reality. That especially presumes there will not be some major, new climate forcing like a major volcanic eruption, an asteroid strike or a regional nuclear war (If there is a global nuclear war, the forecast doesn't really matter...) to throw the climate completely off-track.

[On a bit of a speculative tangent: I find the behaviour of the global temperature in the post-Pinatubo period quite intriguing. The focus of volcanoes and climate seems primarily on the immediate cooling. We see that cooling here. As this post-eruption cooling fades, the result is what appears to be an amplifying oscillation, which culminates in the 1997-8 El Nino event. Are the two things related? Perhaps conincidentally, the similarly huge 1982-3 El Nino also closely follwed a major volcanic eruption...]

If the model is correct, in the next few years natural variability — mainly in factors affecting the heat content of the ocean — will offset some of the climate warming resulting from humanity's greenhouse emissions. But global warming will be taking only a brief breather: half the years from 2009 to 2014 will be warmer than 1998, which is currently the warmest year on record.

Again, I can;t really see the predictions being correct in anything but a broad sense...it's going to get warmer by so much by some time

This prediction is still rather tentative, though. While setting up the initial conditions helps, the various inherent difficulties in the model's attempts to capture all the processes going on mean that the system's forecasts will be far from perfect. The predicted temperatures carry healthy error bars, but Smith points out that the flattening it foresaw in the first few years seems so far to be accurate.

I think this guy sums it up pretty well...

"This study is not primarily important for the brave temperature prediction it makes," he says. "The key thing is that we now have a convincing concept for combining observations and models. It may not be the last word, but it does prove that concrete decadal predictions are possible."

Another area of interest: How is this going to be used for, say, future public planning? Someone, somewhere (justifiably) is going to want to do something along those lines. How do these predictions get turned into useful proposals/actions? What happens when the prediction goes wrong (or at least different)? Who gets blamed in our litigious society?

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