Orbital-Scale Climate Change

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1 Orbital-Scale Climate Change Climate Needed for Ice Age Warm winter and non-frozen oceans so lots of evaporation and snowfall Cool summer so that ice does not melt Ice Age Model When ice growing ocean saltier (not freeze in winter) ocean warmer (fewer ice bergs & less cold runoff thus more evaporation to provide winter precipitation albedo of ice make it more difficult to melt in summer When ice melting water from melt is fresh so ocean freezes in winter ocean cold from melt water so less evaporation less evaporation means less snowfall in winter albedo decreases in summer so more melting Milankovitch Theory Obliquity of Ecliptic - variation of tilt of earth relative to plane of orbit caused by torque of Sun & Moon on Earth Eccentricity of Earth s orbit (ellipticity) caused by pull of Jupiter on Earth Precession of Equinoxes - date of Perihelion caused by torque of Sun & Moon on Earth 1

2 Tilt of Earth s Axis gives us seasons Effect of Tilt on Polar Regions Obliquity of Ecliptic For Ice Age need less tilt Tilt presently high, but decreasing Long Term Changes in Tilt 41,000 Year Cycle Precession of Equinoxes Precession of the Earth s Axis 2

3 Precession of the Ellipse Milankovitch Cycles Precession of the Equinoxes Combined effect of Precession of the Earth s Axis and Precession of the Ellipse Period = 23,000 years Precession of the Equinoxes Precession of Equinoxes Need Summer Solstice near aphelion Near now, but tilt wrong 3

4 Eccentricity of Earth s Orbit Change in Eccentricity of Earth s Orbit 100,000 year cycle Change of Eccentricity High eccentricity enhances precession difference Low eccentricity today, but also low 20,000 yr ago Precession of the Equinox Angle between the Perihelion and Vernal Equinox Extreme Solstice Positions Eccentricity Modulating Precession 4

5 Maximizing Three Cycles Eccentricity Modulated Precession Over last 1.65 Million Years June Insolation Variations Combining Cycles December Insolation Variations 5

6 Solar Insolation Summer Solstice = 90, Winter Solstice = 270 Solar Insolation Summer Solstice = 90, Winter Solstice = 270 Geological Features vs Irradiance Irradiance vs Oxygen Ratio Temperature Power Spectrum 6

7 Ice Volume Lags Insolation Ice Volume Lags Tilt and Precession Bedrock Sinking Bedrock (Positive) Feedback to ice growth and melting Solar Radiation versus Ice Volume Oxygen Isotope Record During Last Ice Age 7

8 Oxygen Ratio Temperature Cores from Eastern Pacific Evidence of Ice Sheet Evolution Climate Change Widespread Northern Hemisphere Glaciations Begin Determining Past Atmospheric Composition from air trapped in Glacial Ice Carbon Dioxide vs Ice Volume Carbon Dioxide versus Ice Volume 8

9 Methane in Past Atmospheres Marine versus Ice Core Temperatures Methane versus Temperature (Fig ) Decreased Carbon Dioxide during Glaciations More CO 2 dissolves in cold water Atmospheric CO 2 drops by 9 ppm for o C cooling Total drop during Ice Age about 22 ppm CO 2 dissolves easier in less salty water During Ice Age salinity increased about 1.2% Thus Atmospheric CO 2 increased by about 11 ppm Other Causes of CO 2 Change Pollen suggests drier and less vegetation About 25% less so carbon not stored here If less CO 2 in Atmosphere then less in near surface ocean (about 25%) Not enough time to exchange with rocks Thus must be in deep ocean 9

10 Carbon Transfer to Deep Oceans During Glaciations Causes of CO 2 Increase in Deep Ocean Greater Winds Cause Greater Upwelling More Arid so Winds Blow Nutrients into Ocean where Photosynthesis increases and Dead Organic Matter Falls to Ocean Floor Deep Ocean Currents Decrease and corrosive water dissolves Carbonates that are brought to the surface where they combine with CO 2 to form Bicarbonates Less Surface Water CO 2 makes for less Atmospheric CO 2 During Glaciation (Fig ) Ice Sheets (Fig 9-4) North American Ice Extent Response to Changes in Atlantic Conveyor Belt (Fig ) 10

11 Vegetation during last Ice Age Extent of Last 4 Glaciers North American Ice Retreat Retreat of Glacier in North America (Fig. 13-2) Great Lakes Ice Withdrawal Lakes Formed During Deglaciation (Fig ) 11

12 Routes of Meltwater Flow (Fig. 13-8) Colder Temperatures accumulated less snow in Greenland and made Stronger winds in Venezuela Polar Front at various Times (Fig. 13-6) Pollen in Minnesota after last Ice Age (Fig. 12-9) European Ice Age European Vegetation (Fig ) 12

13 Ice Age in Europe European Ice Retreat Changes in Europe Last 80,000 years (Fig. 14-6) Ice Volume and Temperature versus Pollen in France (Fig. 11-9) African Monsoon Sand Dunes Now versus Last Glaciation (Fig. 12-5) 13

14 Glacial Australia and South America were Drier Antarctica Winter Sea Ice (Fig ) 14