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
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 • 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 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
North 1000’s km South 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 • 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 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  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.  Paillard, D. (2006) “What drives the ice age cycle”, Science, 313, 455-456
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 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 What does the past tell us about the future?
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  Ruddiman, W.F. (2001) Earth’s Climate Past and Future, http://www.whfreeman.com/ruddiman/ (figures used here)  Paillard, D. (2006) “What drives the ice age cycle”, Science, 313 455-456  Ruddiman, W.F. (2006) “Orbital changes and climate”, Quaternary Science Reviews, 25 3092-3112  Zeng, N. (2007) “Quasi-100ky glacial-interglacial cycles triggered by subglacial burial carbon release”, Climate of the Past, 3 135-153  Huybers, P. (2007) “Glacial variability over the last two million years…”, Quaternary Science Reviews, 26 37-55  Johnston, T.C., Alley, R.B., (2006) “Possible role for dust or other northern forcing …”, Quaternary Science Reviews, 25 3198-3206  Courtillot, V., et al., (2007) “Are there connections between the Earth’s magnetic…”, Earth and Planetary Science Letters 253 328-339  Petit, J.R., et al., (1999) “Climate and atmospheric history of the past 420,000 years…”, Nature 399 429-436  Muller, R.A., MacDonald, G.J., (2000) Ice Ages and Astronomical Causes, Praxis Publishing Ltd.