We thank Alistair Adcroft, Mick Follows, John Marshall, Jeff Scott, and Carl Wunsch for valuable comments on earlier versions of this manuscript. Comments by two reviewers led to considerable improvement. JM was supported by the Tokyo Electric Power Company through the TEPCO/MIT Environmental Research Program, by NSF Grant OCE-9801800, and to 40% ($6000) jointly by the Northeast Regional Center of the National Institute for Global Environmental Change and by the Program for Computer Hardware, Applied Mathematics, and Model Physics (both with funding from the U.S. Department of Energy). BAK was supported by NSF Grant OCE-9521138.
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