Estimate of climate sensitivity from carbonate microfossils

Introduction Conclusions References Tables Figures Back Close Full Screen / Esc This discussion paper is/has been under review for the journal Climate of the Past (CP). Please refer to the corresponding final paper in CP if available. Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Abstract Climate sensitivity is a crucial parameter in global temperature modelling. An estimate is made at the time 33.4 Ma using published high-resolution deep-sea temperature proxy obtained from foraminiferal δ 18 O records from DSDP site 744, combined with published data for atmospheric partial pressure of CO 2 (pCO 2) from carbonate micro-5 fossils, where δ 11 B provides a proxy for pCO 2. The pCO 2 data shows a pCO 2 decrease accompanying the major cooling event of about 4 • C from greenhouse conditions to ice-cap conditions following the Eocene-Oligocene boundary (33.7 My). During the cooling pCO 2 fell from 1150 to 770 ppmv. The cooling event was followed by a rapid and huge increase in pCO 2 back to 1130 ppmv in the space of 50 000 yr. The large pCO 2 in-10 crease was accompanied by a small deep-ocean temperature increase estimated as 0.59 ± 0.063 • C. Climate sensitivity estimated from the latter is 1.1 ± 0.4 • C (66 % confidence) compared with the IPCC central value of 3 • C. The post Eocene-Oligocene transition (33.4 Ma) value of 1.1 • C obtained here is lower than those published from Holocene and Pleistocene glaciation-related temperature data (800 Kya to present) but 15 is of similar order to sensitivity estimates published from satellite observations of tropo-spheric and sea-surface temperature variations. The value of 1.1 • C is grossly different from estimates up to 9 • C published from paleo-temperature studies of Pliocene (3 to 4 Mya) age sediments. The range of apparent climate sensitivity values available from paleo-temperature data suggests that either feedback mechanisms vary widely 20 for the different measurement conditions, or additional factors beyond currently used feedbacks are affecting global temperature-CO 2 relationships.