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James Hansen
Director, NASA’s Goddard Institute for Space Studies, New York, New York, USA

Paleoclimate Record Points Toward Potential Rapid Climate Changes AGU Fall Meeting Dec. 6, 2011. James Hansen
Director, NASA’s Goddard Institute for Space Studies, New York, New York, USA

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James Hansen
Director, NASA’s Goddard Institute for Space Studies, New York, New York, USA

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  1. Paleoclimate Record Points Toward Potential Rapid Climate ChangesAGU Fall Meeting Dec. 6, 2011 James Hansen
Director, NASA’s Goddard Institute for Space Studies, New York, New York, USA EelcoRohling
Professor of Ocean and Climate Change, Southampton University, Southampton, United Kingdom 
Ken Caldeira
Senior Scientist, Department of Global Ecology Carnegie Institutution of Washington, Stanford University, Stanford, California, USA

  2. Basis of Understanding 1. Earth’s Paleoclimate History 2. On-Going Global Observations 3. Climate Models/Theory

  3. 50 million years ago (50 MYA) Earth was ice-free. Atmospheric CO2 amount was of the order of 1000 ppm 50 MYA. Atmospheric CO2 imbalance due to plate tectonics ~ 10-4 ppm per year.

  4. Cenozoic Era End of Cretaceous (65 My BP) Present Day

  5. Climate Change over Cenozoic Era 1. Dominant Forcing: Natural ΔCO2 - Rate ~100 ppm/My (0.0001 ppm/year) - Human-made rate today: ~2 ppm/year Humans Now Overwhelm Slow Geologic Changes

  6. Climate Sensitivity 1. Depends on Climate Forcing - Usually 2XCO2 (4W/m2 forcing) 2. Depends on Climate State - Usually today’s climate 3. Depends on Time Scale - Usually “Equilibrium” for Fast Feedbacks (Ice Sheets fixed, Methane Hydrates fixed)

  7. Global deep ocean temperature. Past 5,300,000 years. Past 500,000 years.

  8. Climate forcings during ice age 20 ky BP, relative to the present (pre-industrial) interglacial period.

  9. Figure 2. Global temperature relative to peak Holocene temperature (Hansen and Sato, 2011).

  10. Fig. 3. (A) Decay of instantaneous injection or extraction of atmospheric CO2, (B) CO2 amount if fossil fuel emissions are terminated at the end of 2010, 2030, or 2050.

  11. Fig. 6. CO2 emissions by fossil fuels (1 ppm CO2 ~ 2.12 GtC). Estimated reserves and potentially recoverable resources are from EIA (2011) and GAC (2011).

  12. Ice Sheet and Sea Level Response EelcoRohling Professor of Ocean and Climate Change, Southampton University, Southampton, United Kingdom

  13. Sea level and GHG forcing – geological context 40 Million years 10 Million years W/m2 500,000 years In natural context, the ‘equilibrium’ sea level for current anthropogenic forcingis 25 ±3m higher than today. This is a measure of the climate disequilibrium. Full adjustment takes time (likely millennia) Large disequilibrium creates increased likelihood of abrupt adjustments Unpublished with G. Foster

  14. How fast did rises occur above the present, in recent geological past? Last Interglacial Structure of two main & one minor peak, separated by lowstands, corroborated by stratigraphic reef sequences (Bruggemann et al., 2004) 3 2 1 2 1 3 Rohling et al. Nature Geoscience 1, 2008 A modelled “best estimate” Eemian Greenland ice sheet (Cuffey and Marshall, 2000) • world max. 1 °C warmer than today and Greenland up to 3-5 °C warmer • meansea-level highstand4-6 m above present • up to half due to Greenland reduction • but not all, so Antarctica was involved! • we find rates of rise above 0m of 1 to 2.5 m/century • similar rates reported since (esp. near lower end) RATES

  15. Climate sensitivity overview paper (in progress; Paleosens working group) T increase for CO2 doubling (°F , °C) Climate sensitivity in °C per W/m2 13.3 7.4 10.1 5.6 4.8 8.6 6.7 3.7 2.6 4.7 3.4 1.9 0.0 0.0 Individual study or compilation • Differences stem from different definitions, different reference systems, and different time-periods considered between studies. • Schmittner et al. (Science) based on LGM is № 18. • Rohling et al. (J. Clim in press) based on last 500,000 years is №s 9 and 10. • Deep time warm climate values are №s 11 to 16.

  16. Radiativeforcing and climate responsefrom paleoclimateto future Ken Caldeira 6 Dec 2011 kcaldeira@carnegie.stanford.edu

  17. There is no one number that is climate sensitivity • Scientists estimate how much climate will change under conditions where some factors are allowed to vary and others are held constant. The answer depends on which factors are held constant and which vary • Greenhouse gas concentrations • Aerosol concentrations • Ice sheets • Land-cover change / Ecosystem distributions • Atmosphere and ocean circulation • Clouds • Etc

  18. Event 55 million years ago (PETM) suggests, with long-term feedbacks, 5.5 - 8 ⁰C ( 10 - 14 ⁰ F) per CO2-doubling Pagani et al 2006

  19. (m) Antarctica = 61.1 m Greenland = 7.2 m Caldeira, ICDC meeting, 2005

  20. Fleming et al. 1998, Fleming 2000, Milne et al. 2005

  21. Climatically important amounts of carbon dioxidewill remain in the atmosphere for thousands of years 3 Number of CO2-doublings 2 1 0 Archer et al 2009

  22. Morality Science Values Facts

  23. Morality Science Values Facts Good Policy

  24. For more information: http://www.giss.nasa.gov/research/briefs/hansen_15/ http://pubs.giss.nasa.gov/abs/ha05510d.html For press inquiries: Patrick Lynch patrick.lynch@nasa.gov 757-897-2047

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