Climate change causes

Climate change causes

1. Solar radiation

   • Lack of conclusive data
   • Sunspot activity
     • Formation related to suns magnetic field
     • Temperature drops in sunspot areas
       • Overall temperature of sun increases
         • Increases solar radiation
           • Less than 1% change
             • 0.03 degrees change
     • 11 year cycles
       • Henrick Schwabe. 1843
       • Foakal, 1990

2. Atmospheric composition

   • Effects radiation budget
   • Benjamin franklin
     • First person to identify potential of volcanic activity to alter climate
       • Cold winter in 1783-84 caused by volcanic dust cloud
         • Iceland July 1783
   • Volcanic eruptions inject dust and sulphur dioxide into atmosphere
     • Mainly converted into sulphuric acid aerosols
       • Suspended in atmosphere for several years
         • Reflect solar radiation
           • Less reaches earths surface and causes cooling
     • Mt pinatubo injected 20 million tonnes sulphur compounds into stratosphere
       • 1991
       • Caused drop in temperature in early 90s
     • Krakatoa 1883
   • Large igneous provinces
     • Superplumes
       • Originate from the core mantle boundary
     • Increase warming by increasing greenhouse gas concentration

3. The earths surface

   • Plate tectonics
     • Large climatic contrasts
       • Causes climate change over 10s of millions years
       • Continuously alters configeration of continents and ocean basins
         • Physical processes influenced by this distrubution
           • Continents at high latitudes allows for more ice at the surface
             • Increases earths albido
             • Blocks ocean currents towards the poles
               • limits transport of heat
             • Causes cooling of climate
   • Polar position hypothesis
     • Theory
       • Ice sheets appear on continents located in polar or near polar latitudes
       • No ice should appear on continents located outside of the polar regions
     • Evidence
       • Shows continents must be at high latitudes to form ice sheets
       • Continents at high latitudes does not garantee the formation of ice sheets
         • Ruddiman, 2008
   • Ocean gateways and barriers
     • Opens or blocks communication between earths oceans
       • Changes oceanic circulation patterns
         • Influences transport of heat
     • Opening of the Drake passage
       • Miocene era
       • Below south america
       • Allowed for flow of cool water across the antarctic
         • Associated with growth of antarctic ice sheets during this time
     • Closing of the passage between the indian and mediterranean ocean
       • Prevented warm water flowing to the atlantic ocean
   • Uplift weathering hypothesis
     • Chemical weathering of rock drives climate change
       • Increased exposed rock with increased uplift
         • Steep slopes
         • Mass wastings
         • Mountain glaciers
         • Slope precipitation
     • Faster weathering draws more CO2 out of the atmosphere
       • Cools climate

4. Eustatic variation

   • Temperature and sea level change
     • Cool climate associated with low sea level
       • e.g. caarboniferous-permian
     • Warmth associated with high sea level
       • Cretatious
         • Lower cretatious has higher exposed land than the upper cretacious
         • 18% land exposed at maximum sea level
           • 28 today
         • Cause of sea level rise
           • Positive feedback
           • Ice caps melted
             • More water in the hydrosphere
               • Sea levels rise
           • Thermal expansion of ocean water
             • Higher volume of ocean water
           • Plate tectonics
             • Increased spreading at oceanic ridge
               • Ridge area expands
               • Ocean basins regionaly elevated
                 • Hot, bouyant crust
                 • Marine transgression
                   • Water displaced from ocean basins to continental land masses
                   • Opposite is called marine regression
     • Oceans absorb more solar radiation
       • Positive feedback

5. Milankovic cycles

   • Variations on earths orbital charecteristics
   • Precession
     • Gravitational interaction with other planets
     • Causes changes in earths distance from the sun
       • Closest distance 153 million Km today
         • Perihelion
         • 3rd Jan today
           • 10000 years ago in mid june
       • Furthest distance 158 million Km today
         • Aphelion
         • July today
           • 10000 years ago in jan
     • 23,000 year cycle
   • Causes latitudal changes in temperature variations
   • Axial tilt
     • 21.5 degrees min
     • 24.5 degrees max
     • 41,000 year cycle
     • Effects distribution of solar radiation in the hemispheres
       • Amplify or suppess strength of seasons
         • especially high latitudes
         • Increased tilt means poles are tilted more towards the sun in summer
           • Increase in solar radiation recieved
   • Eccentricity
     • 100,000 year cycle
     • Variety in the elipticle path of the earths orbit
       • More ellipticle path
         • High eccentricity
       • More circular path
         • Low eccentricity
     • Highest effect on global temp.
     • Evidence
       • 8 glaciations over past 700,000 years
   • Proxy data shows cyclic behaviour every 19000- 24000 years, 43000 years and 100,000 years
   • Cyclothem evidence
     • Cyclic variations shown by sedimentary layering
       • Limestone
         • High sea level
       • Sandstone
         • Shallow marine
       • Mudstone/shale
         • Erosion of nearby land mass
       • Coal layers
         • Sequence becomes exposed
     • Rises and falls in sea levels
       • Believed to be controlled by eccentricity
         • Tucker 2009
       • Smaller variations within the cyclothem