HR: 15:25h
AN: PP22B-08    [PDF]
TI: Estimating climate sensitivity from paleo-data.
AU: * Crowley, T J
EM: tcrowley@duke.edu
AF: Duke University, Dept. Earth and Ocean SciencesBox 90227, Durham, NC 27514 United States
AU: Hegerl, G C
EM: hegerl@duke.edu
AF: Duke University, Dept. Earth and Ocean SciencesBox 90227, Durham, NC 27514 United States
AB: For twenty years estimates of climate sensitivity from the instrumental record have neen between about 1.5-4.5$\deg$C for a doubling of CO2. Various efforts, most notably by J. Hansen, and M. Hoffert and C. Covey. have been made to test this range against paleo-data for the ice age and Cretaceous, yielding approximately the same range with a "best guess" sensitivity of about 2.0-3.0$\deg$C. Here we re-examine this issue with new paleo-data and also include information for the time period 1000-present. For this latter interval formal pdfs can for the first time be calculated for paleo data. Regardless of the time interval examined we generally find that paleo-sensitivities still fall within the range of about 1.5-4.5$\deg$C. The primary impediments to more precise determinations involve not only uncertainties in forcings but also the paleo reconstructions. Barring a dramatic breakthrough in reconciliation of some long-standing differences in the magnitude of paleotemperature estimates for different proxies, the range of paleo-sensitivities will continue to have this uncertainty. This range can be considered either unsatisfactory or satisfactory. It is unsatisfactory because some may consider it insufficiently precise. It is satisfactory in the sense that the range is both robust and entirely consistent with the range independently estimated from the instrumental record.
DE: 3309 Climatology (1620)
DE: 3344 Paleoclimatology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting