Since 1883 there has been a peak or a trough in the trend line roughly every 30 years. Your guess as to what will happen in the future is as good as mine.
On 25 March 2012, the above paragraph was hanged with '30' replacing '25. The following was also added.
In the next graph we look at the 30-ear trend for 7 models. The choice of models was based on those listed on Table 6 of the IPCC “General Guidelines on the Use of Scenario Data for Climate Impact and Adaptation Assessment”, Version 2, June 2007. Where a model has more than one published simulation its results were average before being include in the graph. The siulation results come from the climate explorer site.
Elswhere we have shown the results of the same seven models. Showing the difference as 30-year trends appears to demonstrate how widely different the simulations of the models were.
3 comments:
I think it would be interesting to graph the same thing for the individual model runs, rather than just the ensemble average. Then one would get a feel for how big the unforced fluctuations are, at least in the models.
I've done what you suggested and it does indeed shown that the models give widely different results.
Well, this is not exactly what I was asking for. Ideally, one would show several realizations of the same model with different initial conditions. The point is that some aspects of the dynamics are chaotic, so, even if the model has perfect physics, you do not expect it to match the observed data. The best it can do is to match the trend and statistical aspects of the fluctuations.
What you show is good enough, though, to illustrate that there is nothing unusual in the fluctuations of the data (for instance the fact that there are periods of negative trend) compared to the models.
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