Natural Forcing and Climate Change in the Geological Past

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  • Natural Forces and Climate Change in the Past
    • Milankovitch Cycles
      • Changes in the Earth's axis, orbit and the procession of the exquinoxes
        • Affect the amount of solar radiation reaching the planet's surface and its spatial and temporal distribution
          • Operate on time scales that vary from 10,000 to 100,000 years
            • Milankovitch identified cycles at 100,000, 43,000, 24,000 and 19,000
              • Long glacial periods followed by shorter inter-glacials
    • Volcanic Eruptions
      • Explosive eruptions pump huge amounts of volcanic ash and sulphur dioxide into the stratosphere
        • Have the potential to change the global climate, at least in the short term
          • Volcanic ash is quickly removed, but sulphur dioxide is more persistent and has a cooling effect
            • Is converted into sulphuric acid which forms sulphate aerolsols
              • Reflect solar radiation back into spaced and lower the temperature in the troposphere
                • Mount Pinatubo: Ref. Case Study
    • Ocean Circulation
      • Ocean currents are a vital component of the global energy budget, transferring surplus energy from the tropics to the poles
        • Continental drift can modify ocean circulation and energy transfer
    • Natural Greenhouse Gases
      • There is a close relationship between atmospheric  CO2 levels and the average global temperatures
        • Periods of ice house correspond with with low levels of CO2 in the atmosphere which reduce the Earth's natural greenhouse effect
    • Solar Output
      • The Sun's output is not constant but varies over time
        • There is a positive correlation between the number of sunspots and solar energy output
          • A decrease in sunspots from 0.1% to almost 0 can be seen to be accountable for 'The Little Ice Age' in Europe
            • Recently there have been more sunspot activity, which coincides with recent warming of the global climate

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