Geography paper 1

• The amount of heat from the Sun varies around the Earth. Heat is distributed by pressure differences and ocean currents.
• Ocean currents


  1. Cold, salty water sinks at the Poles

  2. It then flows towards the Equator and is warmed again, creating a convection current
• Pressure differences


  1. Land heats quickly in summer and cools quickly in winter, forming areas of low pressure in summer and high pressure in winter

  2. Sea takes longer to heat and cool, forming high pressure in summer and low pressure in winter
• Inter-Tropical Convergence Zone (ITCZ)


  Occurs near the Equator between the two Hadley Cells, where warm tropical air converges at the Equator
• The Sun's radiation is most intense at the Equator, causing warm tropical air to rise rapidly. This creates an area of low pressure that brings heavy rainfall.
• As the rising air moves away from Equator, it loses its moisture and density, descending to form arid regions.
• Global circulation model


  • Hadley Cell
  • Ferrel Cell
  • Polar Cell
• Theories explaining past climate change

  • Eruption theory
  • Asteroid collision theory
  • Sunspot theory
  • Orbital change theory
• Ice cores


  Air bubbles contain CO₂ that tell us there have been previous warm and cold periods
• Tree rings


  Each ring in a tree shows a year's growth. In warmer and wetter years, a tree grows more
• Historical sources


  Historical drawings, diaries or newspapers are more recent evidence
• Enhanced greenhouse effect


  Human activities (industry, transport, energy, farming) produce greenhouse gases (carbon dioxide, methane) that trap heat from the Sun and warm the planet
• Developed and emerging countries emit more carbon dioxide than developing countries.
• There has been a near 1°C rise in average temperature since the early 1900s.
• Sea levels have risen over 200mm (thermal expansion) in the same period.
• Arctic sea ice has halved in area since 1980.
• 90% of the world's valley glaciers are shrinking.
• Potential impacts of climate change

  • More frequent floods and droughts
  • Stronger storms (tropical cyclones)
  • Changes to farming (unreliable rainfall)
  • Climate refugees from low-lying areas
• Predicting future climate change is difficult because we don't know how populations and economies may grow. Fossil fuel consumption versus renewable energy and people's lifestyle choices are also unknown factors.
• Tropical cyclone


  A rotating system of clouds and storms that forms over tropical waters (26.5°C) and has winds which can exceed 118 km/h
• Tropical cyclone formation


  1. Warm ocean (exceeding 26.5°C)

  2. Strong winds that draw the warm air up rapidly from the ocean surface

  3. Strong Coriolis force created by Earth's rotation
• Tropical cyclone hazards


  • Strong winds
  • Storm surges
  • Intense rainfall
  • Landslides
• Bangladesh's vulnerability to cyclones

  • Much of its population is rural, living on low-lying flood-prone farmland
  • Urbanisation means increased surface runoff so more rainwater reaches rivers
  • Unplanned settlements have been built on low-lying land prone to flooding
  • Its Gross Domestic Product (GDP) is low, so it is less able to invest in costly flood defences
• Bangladesh's cyclone protection measures

  1. Forecasting

  2. Satellite technology

  3. Warning systems

  4. Evacuation strategies

  5. Surge defences
• Bangladesh has reduced the number of deaths from tropical cyclones by using satellite technology to track cyclones and issuing warnings so that people can evacuate to higher ground and cyclone shelters.
• In May 2009, Cyclone Aila killed 190 people and made 750,000 people homeless in Bangladesh.
• The USA prepares for hurricanes through forecasting, satellite technology, warnings, evacuation systems and storm surge defences.
• In 2005, Hurricane Katrina was the worst hurricane to hit the USA. Satellite technology tracked the hurricane's path and residents of New Orleans were told to evacuate. Many low-income residents could not leave as they did not have a car and couldn't afford the cost of transport, and many elderly residents could not leave due to ill health.
• The storm surge caused the levees (embankments) to collapse which flooded 80% of New Orleans. Faulty maintenance and design of the levees were partly to blame.
• 1,833 people died and it cost the economy US$108 billion. The federal government has been heavily criticised for not doing enough to prepare for and respond to Hurricane Katrina.
• Lithosphere


  The uppermost layer of the Earth, split into continental crust (granite) and oceanic crust (basalt)
• Mantle


  Can be divided into two layers - the thinner asthenosphere, a partly molten 'lubricating' layer under the lithosphere, and the lower mantle which is solid
• Core


  Split into two layers - the outer core is liquid, whilst the inner core is solid because the pressure is so great. The composition of both is iron and nickel
• The Earth is heated by radioactive decay in the core and mantle. Convection currents are caused by the geothermal energy and move tectonic plates.
• Conservative plate boundaries


  Plates slide past each other, causing friction and earthquakes
• Divergent plate boundaries


  Plates move apart and magma rises to fill the gap, forming shield volcanoes
• Convergent plate boundaries


  Plates push together, with the denser oceanic plate being subducted, creating andesitic magma and composite volcanoes
• Richter Scale


  Measures the magnitude of an earthquake, with a logarithmic scale where a 6.0 quake is 10 times more powerful than 5.0
• Earthquakes beneath the seabed can generate a tsunami.
• The 2010 Haiti earthquake had a shallow focus close to the densely populated city of Port-au-Prince, leading to collapsed buildings and over 300,000 deaths.