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How Good Are The UK’s Predictions For Sea Level Rise?

Andrew Montford, GWPF

An extrapolated forecast based on the actual trend to date might be more useful to planners than the Met Office’s predictions.

Over the last few days, I have been reviewing the official forecasts of climate change for the UK, going right back to the first iteration in 1991. It’s fair to say that so far we have seen nothing like the level of warming that has been predicted for the UK.¬†Today I thought it might be interesting to see how the various forecasts for sea level rise have turned out.

Because local changes in sea level, due to rise and fall of land heights, are much more important for any particular location than the global change, the UK’s official forecasts tend to focus on the global changes, and it’s these that I will examine here.

Back in 1991, the forecast was a simple one-liner, and it’s fair to say it was very pessimistic, with observed sea level rise since that time barely more than half the predicted change (note that the observations only start in 1993, so the baselines are not quite in synch, but the trends are clear):

By the time of the UKCIP02 predictions, a more sophisticated approach had been adopted, in that a range of possible outcomes was given. This has had the desired effect in that the observations now fall squarely within the forecast range, although that range is so wide that I’m not sure that too much back-slapping is in order. Hitting a barn door is hardly cause for celebration. In particular, the worst-case scenario looks far too pessimistic.

If you look at where the observations were at the time of the next set of forecasts in 2009, you might have wondered whether the scientists involved would have been prompted to rein in the worst case somewhat (although they might now point to the slight acceleration thereafter). However, it is clear that they preferred to play safe (albeit at the cost of making the predictions rather less useful): examining UKCP09, it is clear that they have not altered the expectation at all.

I’m left with the overriding impression that a naive forecast based on the trend to date might be more useful to planners than the predictions given by the Met Office.