paleoclimate record points toward potential rapid climate changes agu fall meeting dec 6 2011
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Director, 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 Hansen
Director, 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

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

slide2
Basis of Understanding

1. Earth’s Paleoclimate History

2. On-Going Global Observations

3. Climate Models/Theory

slide3

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.

slide4

Cenozoic Era

End of Cretaceous (65 My BP)

Present Day

slide5
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

slide6
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)

slide7

Global deep ocean

temperature.

Past 5,300,000 years.

Past 500,000 years.

slide8

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

slide10

Figure 2. Global temperature relative to peak Holocene temperature

(Hansen and Sato, 2011).

slide12

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.

slide13

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

Ice Sheet and Sea Level Response

EelcoRohling

Professor of Ocean and Climate Change, Southampton University, Southampton, United Kingdom

slide15

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

slide16

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

slide17

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.
there is no one number that is climate sensitivity
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
slide20

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

slide21

(m)

Antarctica = 61.1 m

Greenland = 7.2 m

Caldeira, ICDC meeting, 2005

slide23

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

slide24

Morality

Science

Values

Facts

slide25

Morality

Science

Values

Facts

Good

Policy

slide26

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

[email protected]

757-897-2047

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