James HansenDirector, NASA’s Goddard Institute for Space Studies, New York, New York, USA
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Paleoclimate Record Points Toward Potential Rapid Climate Changes AGU Fall Meeting Dec. 6, 2011 James HansenDirector, NASA’s Goddard Institute for Space Studies, New York, New York, USA Eelco RohlingProfessor of Ocean and Climate Change, Southampton University, Southampton, United Kingdom Ken CaldeiraSenior Scientist, Department of Global Ecology Carnegie Institutution of Washington, Stanford University, Stanford, California, USA
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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 - PowerPoint PPT Presentation
Transcript of James HansenDirector, 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 HansenDirector, NASA’s Goddard Institute for Space Studies, New York, New York, USA
Eelco RohlingProfessor of Ocean and Climate Change, Southampton University, Southampton, United Kingdom
Ken CaldeiraSenior Scientist, Department of Global Ecology Carnegie Institutution of Washington, Stanford University, Stanford, California, USA
Basis of Understanding
1. Earth’s Paleoclimate History
2. On-Going Global Observations
3. Climate Models/Theory
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.
Cenozoic Era
End of Cretaceous (65 My BP) Present Day
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
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)
Global deep ocean temperature.
Past 5,300,000 years.
Past 500,000 years.
Climate forcings during ice age 20 ky BP, relative to the present (pre-industrial) interglacial period.
Figure 2. Global temperature relative to peak Holocene temperature (Hansen and Sato, 2011).
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.
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).
Ice Sheet and Sea Level Response
Eelco RohlingProfessor of Ocean and Climate Change, Southampton University, Southampton,
United Kingdom
Sea level and GHG forcing – geological context
500,000 years
10 Million years
40 Millionyears
In natural context, the ‘equilibrium’ sea level for current anthropogenic forcing is 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
W/m2
123
RATES
Rohling et al. Nature Geoscience 1, 2008
Structure of two main & one minor peak, separated by lowstands, corroborated by stratigraphic reef sequences (Bruggemann et al., 2004)
1
2
3
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
mean sea-level highstand 4-6 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)
How fast did rises occur above the present, in recent geological
past? Last Interglacial
Climate sensitivity overview paper (in progress; Paleosens working group)
• 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.
Individual study or compilation
Clim
ate
sens
itivi
ty in
°C p
er W
/m2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 180
0.5
1
1.5
2
2.5
lowhigh
0.0
1.9
3.7
5.6
7.4
T increase for CO2 doubling (°F , °C)
2.6
4.8
0.0
3.4
6.7
10.1
13.3
4.7
8.6
Radiative forcing and climate responsefrom paleoclimate to future
Ken Caldeira6 Dec 2011
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
Pagani et al 2006
Event 55 million years ago (PETM) suggests, with long-term feedbacks, 5.5 - 8 ⁰C ( 10 - 14 ⁰ F) per CO2-doubling
Antarctica = 61.1 mGreenland = 7.2 m
Caldeira, ICDC meeting, 2005
(m)
Fleming et al. 1998, Fleming 2000, Milne et al. 2005
3
2
0
1Num
ber o
f CO
2-dou
blin
gs
Archer et al 2009
Climatically important amounts of carbon dioxidewill remain in the atmosphere for thousands of years
Facts ValuesScience Morality
Facts Values
GoodPolicy
Science Morality
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
757-897-2047
