Climate Physics and the Problem of Abrupt Climate Change

Presentation given to theGEO 302C

April 8, 2005

Charles JacksonInstitute for GeophysicsUT-Austin

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

The real world (in blue) responds with fits and starts to continuous changes in solar forcing.

~25C

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) )

Greenland iceproxy for airtemperature

Indian OceanSpeleothem

proxy for Asian

monsoon

(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.

Multiples of 1470-year spacing between events.

Problem #3…..unknown pace maker

•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