Transcript Climate Physics and the Problem of Abrupt Climate Change

Climate Physics and the Problem of
Abrupt Climate Change
Charles Jackson
Institute for Geophysics
UT-Austin
Presentation given to the
GEO 302C
April 8, 2005
Climate model (in black) responds smoothly to continuous
changes in solar forcing over the past 165 thousand years.
Greenland ice core proxy record for
annual mean air temperature
o
~25 C
The real world (in blue) responds with fits and starts to
continuous changes in solar forcing.
Climate model predictions of future climate
(Climate Change, IPCC 2001)
(Climate Change, IPCC 2001)
(Climate Change, IPCC 2001)
abrupt climate change requires:
• A trigger
• An amplifier
• A source of persistence
Two complimentary theories
• Theory for ice sheet instability
• Theory for the existence of two stable
steady states for the ocean’s meridional
overturning circulation (the MOC)…also
called the thermohaline circulation.
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 ocean’s 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)
A 3-box model of the MOC
Two stable solutions
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.
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?
Abrupt climate change events seen globally
(Lynch-Stieglitz, 2004 as compiled from Voelker, (2002) )
Indian Ocean
Speleothem
proxy for
Asian
monsoon
Greenland ice
proxy for air
temperature
(Burns et al, 2003)
Climate Model Simulation of the Collapse of the
Meridional Overturning Circulation in Atlantic
(Hadley Centre technical note 26, 2001)
ENSO produces a
wave-like pattern in
temperature and
precipitation.
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.
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.
Afternoon Talks: 1:30 - 4:45
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 - 5:00 - 6:30 A.C.E.S. Atrium
Evening Talk: 7:00 - 8:00
Welch Hall Room 2.224
Lonnie Thompson (Ohio State University)
Ice Adventures: Tracking Evidence of Abrupt Climate Change Across
the Tropics