Climate Physics and the Problem of Abrupt Climate Change

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Climate Physics and the Problem of Abrupt Climate
Change

• Presentation given to the
• GEO 302C
• April 8, 2005

Charles Jackson Institute for Geophysics UT-Austin

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Climate model (in black) responds smoothly to
continuous changes in solar forcing over the past
165 thousand years.
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The real world (in blue) responds with fits and
starts to continuous changes in solar forcing.
Greenland ice core proxy record for annual mean
air temperature
25oC
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Climate model predictions of future climate
(Climate Change, IPCC 2001)
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(Climate Change, IPCC 2001)
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(Climate Change, IPCC 2001)
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abrupt climate change requires

• A trigger
• An amplifier
• A source of persistence

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Two complimentary theories

• Theory for ice sheet instability
• Theory for the existence of two stable steady
  states for the oceans meridional overturning
  circulation (the MOC)also called the
  thermohaline circulation.

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Binge-Purge Hypothesis

• Geothermal heating at the base of the Laurentide
  ice sheet caused a periodic collapse of the
  portion of ice above Hudson Bay.
• Ice bergs would flood the North Atlantic,
  depositing ice rafted debris and shutting down
  the oceans meridional overturning circulation
• Timing of 1) ice sheet recovery and 2) geothermal
  heat accumulation at ice base determine 7 to 10
  kyr time scale between events.

(MacAyeal 1993)
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A 3-box model of the MOC
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Two stable solutions
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Problem 1.

• It would appear that there were multiple sources
  of ice rafted debris at the same time.
• On short time scales, ice sheets are thought to
  be well insulated from changes in external
  forcing.so one would expect only a single source
  of ice rafted debris.

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Problem 2 the global extent of D/O events

• D/O events are seen almost everywhere, however
  modeled response to MOC shutdown restricted to
  North Atlantic
• Only changes in CO2 are thought to affect global
  temperatures.
• Changes in tropics?...what is controling system
  memory?

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Abrupt climate change events seen globally
(Lynch-Stieglitz, 2004 as compiled from Voelker,
(2002) )
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Indian Ocean Speleothem proxy for Asian monsoon
Greenland ice proxy for air temperature
(Burns et al, 2003)
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Climate Model Simulation of the Collapse of the
Meridional Overturning Circulation in Atlantic
(Hadley Centre technical note 26, 2001)
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ENSO produces a wave-like pattern in temperature
and precipitation.
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Problem 3..unknown pace maker
Multiples of 1470-year spacing between events.

• Standard deviation between interval spacing is
  only 2
• 11-year sunspot cycle varies in period by -14
• Closest known orbital cycle is a lunar cycle of
  1,800 years.

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Summary

• Relative to what is observed in nature, climate
  models seem unusually stable.
• There are many mysteries surrounding the cause
  and mechanisms of past abrupt climate change.
• Although future abrupt climate change is
  considered unlikely, model predictions of future
  climate may be under-representing the potential
  for such extreme events.

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Afternoon Talks 130 - 445 Applied Computational Engineering and Sciences Building - A.C.E.S. Afternoon Talks 130 - 445 Applied Computational Engineering and Sciences Building - A.C.E.S. Afternoon Talks 130 - 445 Applied Computational Engineering and Sciences Building - A.C.E.S.
Richard Alley (Penn State University)Big Ice Sheet Instability Implications for Future Sea Level
Thomas Stocker (University of Bern, Switzerland)Irreversible Climate Transitions Future Trouble?
Break
Philip Marcus (University of California, Berkeley)Prediction of Abrupt Change in Jupiter's Climate An Analog for Earth?
    Reception - 500 - 630 A.C.E.S. Atrium     Reception - 500 - 630 A.C.E.S. Atrium     Reception - 500 - 630 A.C.E.S. Atrium
    Evening Talk 700 - 800     Welch Hall Room 2.224     Evening Talk 700 - 800     Welch Hall Room 2.224     Evening Talk 700 - 800     Welch Hall Room 2.224
Lonnie Thompson (Ohio State University)Ice Adventures Tracking Evidence of Abrupt Climate Change Across the Tropics Lonnie Thompson (Ohio State University)Ice Adventures Tracking Evidence of Abrupt Climate Change Across the Tropics