causes of climate variation

• Atmosphere circulation:

  • Giant convection systems 
  • Warm air from the equator moves towards the poles 
  • Colder air from the poles moves towards the equator 
• Atmosphere circulation:

  • Equator - rising air (low pressure) so clouds form and it rains 
  • Poles - sinking air (high pressure) so clear skies and it is dry 
• Atmosphere circulation:

  • Assume uniformitarianism and laws of physics are unchanged throughout ages of the planet 
  • So atmosphere circulation should have behaved the same in the past as it does today 
• Ocean circulation:

  • Convection currents occur in the oceans, also spreading heat across the planet 
  • More complex than wind patterns due to land masses - winds can blow across land but currents cannot 
• Shallow:

  • Driven by the sun 
  • Sun heats the planet and creates high and low pressure
  • The wind blows over the ocean and the water drags with it 
• Deep:

  • Driven by density differences 
  • Called a thermohaline current 
• Ocean circulation:

  • Continents move due to tectonics 
  • So over time give different patterns of currents and therefore different climate effects 
• Agulhas current:

  • Eastern of southern Africa 
  • Warms water from tropics fed into Atlantic 
  • Poorly understood - could be involved in countering the cooling of the Atlantic due to glacier melt 
• Gulf stream:

  • Keeps the UK and western Europe warmer than it would be based in latitude 
• Drake passage opening:

  • 40 ma the drake passage closed 
  • Antarctica kept warm by water flowing to it from the tropics 
  • 30 ma the drake passage opened 
  • Antarctica circumpolar current flows around the edge of Antarctica isolating it from warming tropical waters 
  • Antarctica is cold so ice caps formed 
• Asian monsoon:

  • Summer - Asia landmasses warms faster than the sea so warm air rises and draws moist air from the Indian ocean (wet summer season)
  • Winter - Asia landmasses lose heat rapidly and gets cold. Indian ocean is still warm, so the air rises and draws cold air away from central Asia (dry winter)
• Asian monsoon:

  • Himalayas affect climate 
  • In summer monsoons the warm moist air is blocked and the gobi desert remains dry
  • In winter dry's cold air from central Asia is blocked, so India stays warmer than other parts of Asia 
• Himalayas and ice age:

  • Himalayan uplift started 40 ma 
  • By 10 ma it reached half its current height 
  • Upper atmosphere circulation was disrupted by high mountains - causing ripples 
  • At times the ripples could draw cold air from the poles downwards causinf ice sheet growth 
  • Then positive feedback due to albedo caused further cooling 
  • Rocky mountains and alps also influence the same circulation pattern 
• Himalayas and ice age:

  • During mountain build up there should be more weathering and erosion 
  • Sediments are removed from the mountain and end up buried in the ocean 
  • So CO2 removed from the atmosphere and temperatures cool 
• There are multiple factors and feedbacks. So it is unlikely that one event led to the current icehouse earth.