Reconstruction of a continuous high-resolution CO 2 record over the past 20 million years

• Published in: Climate of the Past
• Main Authors: Van De Wal, R. S.W., De Boer, B., Lourens, L. J., Köhler, P., Bintanja, R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2011
• Subjects: /dk/atira/pure/sustainabledevelopmentgoals/climate_action; name=SDG 13 - Climate Action; /dk/atira/pure/sustainabledevelopmentgoals/life_below_water; name=SDG 14 - Life Below Water; ice core
• Online Access: https://research.vu.nl/en/publications/c7585c0d-48e3-4fa3-ab90-a091a6655e3d; https://doi.org/10.5194/cp-7-1459-2011; https://hdl.handle.net/1871.1/c7585c0d-48e3-4fa3-ab90-a091a6655e3d; http://www.scopus.com/inward/record.url?scp=84255187183&partnerID=8YFLogxK; http://www.scopus.com/inward/citedby.url?scp=84255187183&partnerID=8YFLogxK

The gradual cooling of the climate during the Cenozoic has generally been attributed to a decrease in CO 2 concentration in the atmosphere. The lack of transient climate models and, in particular, the lack of high-resolution proxy records of CO 2 , beyond the ice-core record prohibit, however, a full understanding of, for example, the inception of the Northern Hemisphere glaciation and mid-Pleistocene transition. Here we elaborate on an inverse modelling technique to reconstruct a continuous CO 2 series over the past 20 million year (Myr), by decomposing the global deep-sea benthic δ 18 O record into a mutually consistent temperature and sea level record, using a set of 1-D models of the major Northern and Southern Hemisphere ice sheets. We subsequently compared the modelled temperature record with ice core and proxy-derived CO 2 data to create a continuous CO 2 reconstruction over the past 20 Myr. Results show a gradual decline from 450 ppmv around 15 Myr ago to 225 ppmv for mean conditions of the glacial-interglacial cycles of the last 1 Myr, coinciding with a gradual cooling of the global surface temperature of 10 K. Between 13 to 3 Myr ago there is no long-term sea level variation caused by ice-volume changes. We find no evidence of change in the long-term relation between temperature change and CO 2 , other than the effect following the saturation of the absorption bands for CO 2 . The reconstructed CO 2 record shows that the Northern Hemisphere glaciation starts once the long-term average CO 2 concentration drops below 265 ppmv after a period of strong decrease in CO 2 . Finally, only a small long-term decline of 23 ppmv is found during the mid-Pleistocene transition, constraining theories on this major transition in the climate system. The approach is not accurate enough to revise current ideas about climate sensitivity.