Climate Change 2001:
Working Group I: The Scientific Basis
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There are now a greater number of global coupled atmosphere-ocean models and a number of them have been run for multi-century time-scales. This has substantially improved the basis for estimating long time-scale natural unforced variability. There are still severe limitations in the ability of such models to represent the full complexity of observed variability and the conclusions drawn here about changes in variability must be viewed in the light of these shortcomings (Chapter 8).
Some new studies have reinforced results reported in the SAR. These are:

Some new results have challenged the conclusions drawn in earlier reports, such as:

Finally there are areas where there is no clear indication of possible changes or no consensus on model predictions:

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