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Section 11.4 Long-term climate drivers

Subsection 11.4.1 Geologic and Orbital Effects

Large-Scale Causes of Climate Change

  • continental drift & plate tectonics

  • movement toward poles may result in glaciation

  • cannot explain glacial cycles within an ice age

Milankovitch Cycles

  • insolation changes from Earth’s orbital mechanics

  • exaggerate normal seasonal effects

  • examination of glacial activity at 65°N; approx 100,000 year cycle

  • variations in solar insolation are principle controlling factor

  • orbital effects

    • variation in eccentricity of Earth’s orbit

    • 100,000 and 400,000 year cycles

  • axial tilt

    • variation in angle of Earth’s rotation axis,

    • relative to orbital plane

    • currently 23.5°; 41,000 year cycle

  • precession

    • wobble in Earth’s rotation axis

    • 26,000 year cycle; current pole star is Polaris

Causes of Glaciation

  • ocean currents: in Atlantic, currents transport heat from tropics to higher latitudes

  • solar energy: variations in output; can be tracked by sunspot cycles

  • cause of ice ages remains an area of active research

Subsection 11.4.2 Climate Feedback Loops

positive feedback (increase glaciation)

  • increased ice cover lowers solar absorption (albedo effect)

  • increase in freshwater flow to oceans

negative feedback (decrease glaciation)

  • Milankovitch cycles

  • greenhouse gas concentrations

  • weathering (which removes CO2) decreases during glaciation

  • anthropogenic effects

More generally, positive feedback loops: enhance or accelerate change

  • ice/albedo

  • methane release

  • water-vapor feedback

negative feedback loops: disrupt or mitigate change

  • water/cloud

  • blackbody/height

  • CO2 sequestration