Unit 1: hazardous earth

• Global Atmospheric Circulation


  Winds transfer heat from the Equator to the Poles
• Global Atmospheric Circulation


  1. The Sun heats the Earth's surface more at the Equator than the Poles

  2. Temperature differences create pressure differences

  3. Winds blow from high pressure to low pressure areas, transferring heat away from the Equator

  4. Rising warm air creates low pressure belts, sinking cool air creates high pressure belts

  5. Winds are part of global atmospheric circulation cells
• Atmospheric Circulation Cells


  • Hadley Cell
  • Ferrel Cell
  • Polar Cell
• Surface winds blowing towards the Equator are called trade winds
• Surface winds blowing towards the Poles are called easterlies
• Warm surface winds meet cold air from the Poles


  Warm air is forced to rise, creating low pressure and frontal rain
• Some air moves back towards the Equator, the rest moves towards the Poles
• At the Poles, the cool air sinks, creating high pressure
• Ocean Currents


  Large-scale movements of water that transfer heat energy
• Ocean Currents


  1. Caused by wind, differences in water density, and the rotation of the Earth

  2. Bring warm water from the Equator to the Poles

  3. Bring cold water from the Poles to the Equator

  4. Cause upwelling and downwelling of water
• Climate Zones


  • Arid (Dry)
  • Polar
  • Tropical
• The climate zones are caused by global atmospheric circulation
• Climate Graph


  Shows precipitation and temperature for a location over the year
• The Earth's climate is always changing
• Natural Causes of Climate Change

  • Orbital Changes
  • Volcanic Activity
  • Solar Output
  • Asteroid Collisions
• Orbital Changes


  1. Changes in the Earth's orbit around the Sun

  2. Changes in the tilt of the Earth's axis

  3. Precession - the wobbling of the Earth's axis
• Orbital changes


  May have caused the glacial and interglacial periods of the Quaternary
• Volcanic Activity


  Ejection of large quantities of water and particles into the atmosphere, blocking some solar radiation
• The 1815 eruption of Mount Tambora led to the "Year Without a Summer" in 1816
• Solar Output


  Varies in short cycles of about 11 years and possibly longer cycles
• The Maunder Minimum was a period of reduced solar activity between 1645 and 1715, coinciding with the Little Ice Age
• Asteroid Collisions


  Can block solar radiation and cause global cooling
• Evidence for Natural Climate Change


  • Tree Rings
  • Historical Records
  • Ice Cores
• Tree Rings


  1. Trees produce one ring per year

  2. Thickness of rings depends on conditions when formed

  3. Scientists count and measure rings to determine past climate
• Historical Records


  1. Records of weather, harvests, paintings etc. provide information on past climate

  2. For example, records show England was warm enough to grow grapes during the Medieval Warm Period
• Ice Cores


  1. Ice sheets contain layers of ice that accumulate over time

  2. Analysing air bubbles and chemical composition of ice layers reveals past temperatures and atmospheric composition
• One ice core from Antarctica shows temperature changes over the last 400,000 years
• Medieval Warm Period


  A period of warmer climate in Europe between 900 and 1300 AD
• Little Ice Age


  A period of cooler climate that followed the Medieval Warm Period
• The Little Ice Age is evidenced by paintings showing the River Thames freezing over in London
• Natural Greenhouse Effect


  Essential for keeping the planet warm, caused by greenhouse gases trapping heat
• Natural Greenhouse Effect


  1. Incoming solar radiation heats the Earth's surface

  2. Outgoing long-wave radiation is absorbed by greenhouse gases

  3. Greenhouse gases re-radiate some of this heat back to the Earth's surface
• Greenhouse Gases


  Gases that absorb and trap heat in the atmosphere, including carbon dioxide and methane
• Some greenhouse gases are more effective at trapping heat than others
• Greenhouse gases remain in the atmosphere for different lengths of time
• The more greenhouse gases in the atmosphere, the more heat is trapped
• Enhanced Greenhouse Effect


  Human activities are making the greenhouse effect stronger, causing global warming
• Human Activities Increasing Greenhouse Effect


  1. Burning of fossil fuels

  2. Farming practices like livestock production and rice cultivation

  3. Deforestation and land use changes
• Human Activities are Making the Greenhouse Effect Stronger
• There is Some Evidence that Human Activity is causing Climate Change