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Ice ages and Global Warming. David Damm Greg McCormick. EAS 4610. Outline. Earth Temperature History Climate System Forcing and Response Ice sheet response Other feedbacks and responses Future climate. 3 Million yrs. Past 400k yrs. Past 10k yrs - Interglacial. Present Temperatures.

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ice ages and global warming

Ice ages and Global Warming

David Damm

Greg McCormick

EAS 4610

  • Earth Temperature History
  • Climate System Forcing and Response
  • Ice sheet response
  • Other feedbacks and responses
  • Future climate
continental ice sheets
Continental Ice Sheets
  • Accumulation vs. ablation:control extent, thickness, and rate of growth (shrinkage)
  • Topography:flow control, altering of terrain, continental depression, glacial deposits
continental ice sheet equilibrium
Continental Ice Sheet Equilibrium
  • Accumulation:dependent on temperature, precipitation, moisture content of atmosphere
  • Ablation: (melting) strong temperature dependence
  • Slow growth; Rapid decay
  • Glacial cycle characteristic: long, slow period of glacial advance, punctuated by short interglacial period with rapid de-glaciation
orbital forcing and ice sheet response
Orbital forcing and ice sheet response

insolation – solar energy trapped by earth

Ice sheets advance:Obliquity (41k) and precession (23k) combine for minimum insolation

Ice sheets retreat: maximum insolation during summer months

continental ice sheet cycle


1000’s km


Continental Ice Sheet Cycle

A No ice sheet (interglacial)

B Insolation drops (orbital), equilibrium line shifting south

  • ice sheet grows

C Insolation rises, equilibrium line shifting north, (glacial maximum)

D Equilibrium line far north

 rapid decay of ice sheet (deglaciation)

ice age theories
Ice Age Theories
  • Spectral analysis yields dominant frequency of temperature history
  • What is the cause of the 100k cycles?
  • Do CO2 and CH4 lead or lag ice volume and temperature? other feedbacks?
  • How well can ice age models reproduce the history of the last ~3 Myr?
ice age theories1
Ice Age Theories
  • Adhemar (1842) proposed precessional forcing and Milankovitch (1941) included obliquity and eccentricity
  • Greenhouse gas based theories (1800’s): Tyndall, Arrhenius, Chamberlin
  • insolation (alone) and CO2/CH4 (alone) cannot explain the ice age cycles of the last ~3 Myr [2]

Current research efforts focus on better understanding of the interaction between external forcing (insolation) and internal forcing/feedbacks such as: GHG’s, albedo, vegetation, ocean/atmosphere circulation, dust, etc.

[2] Paillard, D. (2006) “What drives the ice age cycle”, Science, 313, 455-456

ice age theories2
Ice Age Theories

Ruddiman (2006):Insolation forcing with GHG forcing at 22k signal, and GHG/albedo feedback at 41k. 100k signal is due to uniquely coincident forcing and feedback.

  • 22k insolation drives monsoon flooding of tropical wetlands producing fast (leading) CH4 response and subsequent forcing on ice volume
  • 44k insolation drives ice volume response which drives lagging GHG response for positive feedback

Zeng (2007):Central process is burial and preservation of organic carbon by icesheets; after prolonged glaciation, subglacial transport becomes sufficient to release buried carbon to atmosphere; CO2 is dominant factor in 5°C cooler glacial climate with contributions from insolation and albedo

ice age theories3
Ice Age Theories

Huybers (2007):Obliquity at 40k period dominates glacial cycles; deglaciations skip one or two beats for 80k or 120k cycles resulting in “apparent 100k variability”; integrated insolation modeling parameter predicts 33 of 36 deglaciations

Johnston, et al., (2006):Role of dust and other northern forcing of CO2 changes

Courtillot, et al., (2007):Earth’s magnetic field effects on climate

future climate change
Future Climate Change

What does the past tell us about the future?

concluding remarks
Concluding Remarks
  • Ice age cycles over the last 3Myr have resulted from complex interactions between external forcing (insolation) and internal forcing/feedbacks such as:
    • greenhouse gases (CO2, CH4)
    • albedo changes (due to changes in ice, vegetation, and clouds)
    • changes in global ocean/atmospheric circulation (resulting in major and rapid regional climate patterns)
  • Ice sheet response to astronomical forcing helps mediate global temperature
  • Anthropogenic GHG emissions have caused a fundamental shift away from natural glacial cycles and towards a warmer climate not seen for millions of years.

References and resources used

[1] Ruddiman, W.F. (2001) Earth’s Climate Past and Future, (figures used here)

[2] Paillard, D. (2006) “What drives the ice age cycle”, Science, 313 455-456

[3] Ruddiman, W.F. (2006) “Orbital changes and climate”, Quaternary Science Reviews, 25 3092-3112

[4] Zeng, N. (2007) “Quasi-100ky glacial-interglacial cycles triggered by subglacial burial carbon release”, Climate of the Past, 3 135-153

[5] Huybers, P. (2007) “Glacial variability over the last two million years…”, Quaternary Science Reviews, 26 37-55

[6] Johnston, T.C., Alley, R.B., (2006) “Possible role for dust or other northern forcing …”, Quaternary Science Reviews, 25 3198-3206

[7] Courtillot, V., et al., (2007) “Are there connections between the Earth’s magnetic…”, Earth and Planetary Science Letters 253 328-339

[8] Petit, J.R., et al., (1999) “Climate and atmospheric history of the past 420,000 years…”, Nature 399 429-436

[9] Muller, R.A., MacDonald, G.J., (2000) Ice Ages and Astronomical Causes, Praxis Publishing Ltd.