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Climate Sensitivity, Sea Level, and Atmospheric Carbon DioxideCenozoic temperature, sea level and CO2 covariations provide insights into climate sensitivity to external forcings and sea-level sensitivity to climate change. Climate sensitivity depends on the initial climate state, but potentially can be accurately inferred from precise palaeoclimate data. Pleistocene climate oscillations yield a fast-feedback climate sensitivity of 3+/-1deg C for a 4 W/sq m CO2 forcing if Holocene warming relative to the Last Glacial Maximum (LGM) is used as calibration, but the error (uncertainty) is substantial and partly subjective because of poorly defined LGM global temperature and possible human influences in the Holocene. Glacial-to-interglacial climate change leading to the prior (Eemian) interglacial is less ambiguous and implies a sensitivity in the upper part of the above range, i.e. 3-4deg C for a 4 W/sq m CO2 forcing. Slow feedbacks, especially change of ice sheet size and atmospheric CO2, amplify the total Earth system sensitivity by an amount that depends on the time scale considered. Ice sheet response time is poorly defined, but we show that the slow response and hysteresis in prevailing ice sheet models are exaggerated. We use a global model, simplified to essential processes, to investigate state dependence of climate sensitivity, finding an increased sensitivity towards warmer climates, as low cloud cover is diminished and increased water vapour elevates the tropopause. Burning all fossil fuels, we conclude, would make most of the planet uninhabitable by humans, thus calling into question strategies that emphasize adaptation to climate change.
Document ID
20140017102
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Hansen, James
(Columbia Univ. New York, NY, United States)
Sato, Makiko
(Columbia Univ. New York, NY, United States)
Russell, Gary
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Kharecha, Pushker
(Columbia Univ. New York, NY, United States)
Date Acquired
December 8, 2014
Publication Date
September 16, 2013
Publication Information
Publication: Philosophical Transactions of the Royal Society A - Discussion Meeting Issue: Warm Climates of the Past - A Lesson for the Future?
Volume: 371
Issue: 2001
Subject Category
Meteorology And Climatology
Report/Patent Number
GSFC-E-DAA-TN16262
Funding Number(s)
CONTRACT_GRANT: NNX10AU63A
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
sea level
climate
palaeoclimate
climate sensitivity

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