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Ice ages and Global Warming

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

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  1. Ice ages and Global Warming David Damm Greg McCormick EAS 4610

  2. Outline • Earth Temperature History • Climate System Forcing and Response • Ice sheet response • Other feedbacks and responses • Future climate

  3. 3 Million yrs

  4. Past 400k yrs

  5. Past 10k yrs - Interglacial

  6. Present Temperatures

  7. Climate system forcing and response

  8. Astronomical Forcing

  9. Continental Ice Sheets • Accumulation vs. ablation:control extent, thickness, and rate of growth (shrinkage) • Topography:flow control, altering of terrain, continental depression, glacial deposits

  10. 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

  11. 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

  12. Orbital forcing and ice sheet response

  13. Continental Ice Sheet Equilibrium

  14. 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)

  15. 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?

  16. 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

  17. 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

  18. 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

  19. Future Climate Change What does the past tell us about the future?

  20. 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, http://www.whfreeman.com/ruddiman/ (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.

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