Deriving global climate sensitivity from palaeoclimate reconstructions

To assess the future impact of anthropogenic greenhouse gases on global climate, we need a reliable estimate of the sensitivity of the Earth's climate to changes in radiative forcing. Climate sensitivity is conventionally defined as the equilibrium surface temperature increase for carbon dioxide doubling, ΔT 2x. Uncertainties in cloud processes spread general circulation model (GCM) estimates of this parameter over the range 1.5< ΔT 2x <4.5°C (refs 1, 2). An alternative to model-based estimates is in principle available from the reconstruction of past climates3–6, which implicitly includes cloud feedback. Here we retrieve the sensitivity of two palaeoclimates, one colder and one warmer than present, by independently reconstructing both the equilibrium surface tem-perature change and the radiative forcing. Our results yield ΔT 2x = 2.3 ±0.9 °C. This range is comparable with estimates from GCMs and inferences from recent temperature observations and ocean models7,8. Future application of the method to additional climates in the geological record might constrain climate sensitivity enough to narrow the model uncertainties of global warming predictions.

[1]  W. Broecker,et al.  Paleotemperatures in the Southwestern United States Derived from Noble Gases in Ground Water , 1992, Science.

[2]  R. Lindzen.  Some Coolness Concerning Global Warming , 1990 .

[3]  Andrew A. Lacis,et al.  Sun and dust versus greenhouse gases: an assessment of their relative roles in global climate change , 1990, Nature.

[4]  J. Houghton,et al.  Climate change : the IPCC scientific assessment , 1990 .

[5]  M. J. Newman,et al.  Implications of Solar Evolution for the Earth's Early Atmosphere. , 1977, Science.

[6]  E. Barron.  Eocene equator‐to‐pole surface ocean temperatures: A significant climate problem? , 1987 .

[7]  Xingjian Jiang,et al.  Revised projection of future greenhouse warming , 1991, Nature.

[8]  J. Jäger,et al.  Climate change: Science, impacts an policy , 1991 .

[9]  Z. X. Li,et al.  Interpretation of Cloud-Climate Feedback as Produced by 14 Atmospheric General Circulation Models , 1989, Science.

[10]  Wallace S. Broecker,et al.  The Carbon cycle and atmospheric CO[2] : natural variations Archean to present , 1985 .

[11]  S. Baliunas,et al.  Evidence for long-term brightness changes of solar-type stars , 1990, Nature.

[12]  John F. B. Mitchell,et al.  THE "GREENHOUSE" EFFECT AND CLIMATE CHANGE , 1989 .

[13]  Y. Izráel',et al.  Prospects for future climate : a special US/USSR report on climate and climate change , 1990 .

[14]  M. Budyko,et al.  Anthropogenic Climate Change , 1991 .

[15]  Syukuro Manabe,et al.  Thermal Equilibrium of the Atmosphere with a Given Distribution of Relative Humidity , 1967 .

[16]  S. Thompson,et al.  Comparison of Cretaceous and Present Earth Albedos: Implications for the Causes of Paleoclimates , 1981, The Journal of Geology.

[17]  M. I. Budyko,et al.  History of the Earth's atmosphere , 1987 .

[18]  W. Peltier,et al.  A model of late Pleistocene ice sheet growth with realistic geography and simplified cryodynamics and geodynamics , 1990 .

[19]  L. Harvey,et al.  Climatic impact of ice-age aerosols , 1988, Nature.

[20]  W. Berger,et al.  History of atmospheric CO2: constraints from the deep-sea record , 1988 .

[21]  C. Lorius,et al.  Ice-core record of atmospheric methane over the past 160,000 years , 1990, Nature.

[22]  A. Callegari,et al.  The role of deep sea heat storage in the secular response to climatic forcing , 1980 .

[23]  T. Crowley.  Are There Any Satisfactory Geologic Analogs for a Future Greenhouse Warming , 1990 .

[24]  V. Ramanathan,et al.  Observational determination of the greenhouse effect , 1989, Nature.

[25]  H. Oeschger,et al.  The environmental record in glaciers and ice sheets : report of the Dahlem Workshop on the Environmental Record in Glaciers and Ice Sheets, Berlin, 1988, March 13-18 , 1989 .

[26]  R. Charlson,et al.  Ice-age dust and sea salt , 1990, Nature.

[27]  J. Coakley,et al.  Climate Forcing by Anthropogenic Aerosols , 1992, Science.

[28]  T. Wigley,et al.  Implications for climate and sea level of revised IPCC emissions scenarios , 1992, Nature.

[29]  R. Berner.  Palaeo-CO2 and climate , 1992, Nature.

[30]  R. Berner.  Atmospheric Carbon Dioxide Levels Over Phanerozoic Time , 1990, Science.

[31]  E. W. Baker,et al.  The post-Paleozoic chronology and mechanism of 13C depletion in primary marine organic matter. , 1989, American journal of science.

[32]  J. Hansen,et al.  The ice-core record: climate sensitivity and future greenhouse warming , 1990, Nature.

[33]  S. Manabe,et al.  A comparison of climate model sensitivity with data from the last glacial maximum. , 1985 .

[34]  Taro Takahashi,et al.  Climate processes and climate sensitivity , 1984 .

[35]  J. Jouzel,et al.  Irregular glacial interstadials recorded in a new Greenland ice core , 1992, Nature.