This new paper (in review at the discussions section) at Climate of the Past has some interesting approaches using

Oxygen 18 isotope records from benthic foraminiferas acquired in Deep Sea Drilling project (DSDP) on the Kerguelen Plateau off the coast of Antarctica and in the Cape Basin off the coast of Namibia. These drill holes provide

18O records with a resolution of order 10 000 yr across the Eocene-Oligocene boundary thus providing an excellent proxy for deep-ocean temperature.

C, for a doubling of pCO2. Where published values are in units C/(Wm−2), the published value is multiplied by 3.7 for the purpose of this comparison. Note that Asten’s median value of 1.1 agrees with Douglas and Christy.

Estimate of climate sensitivity from carbonate microfossils dated near the Eocene-Oligocene global cooling

M. W. Asten

School of Geosciences, Monash University, Melbourne, VIC 3800, Australia

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 δ18O records from DSDP site 744, combined with published data for atmospheric partial pressure of CO 2 (pCO 2 ) from carbonate microfossils, where δ11B 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 icecap 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 increase 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 is of similar order to sensitivity estimates published from satellite observations of tropospheric 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 for the different measurement conditions, or additional factors beyond currently used feedbacks are affecting global temperature-CO 2 relationships.

Discussion Paper (PDF, 1101 KB) Interactive Discussion (Open)

Readers that have access to Climate of the Past can leave a short comment until 30 Nov 2012. You can also watch the open review process as editors and reviewers leave comments. Constructive comments are welcome.

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