Geography hazardous earth part 1

• Global circulation


  1. Hot air rises at equator

  2. Causes low pressure

  3. Air spreads out and sinks at tropics

  4. Causes high pressure

  5. Air flows back towards equator
• ITCZ


  Band of rainfall at the equator
• ITCZ moves


  Due to tilt of Earth's axis as it orbits the Sun
• ITCZ causes rainy seasons in West Africa
• Global circulation cells


  1. Hadley cell

  2. Ferrel cell

  3. Polar cell
• High pressure


  Causes dry, desert conditions
• Low pressure


  Causes rainfall
• Air always flows from high pressure to low pressure
• Ocean currents


  Move heat from equator to poles
• Ocean currents prevent overheating of the planet
• Rainfall zones


  • Rainfall in areas of low pressure
  • Dry, desert conditions in areas of high pressure
• West Africa experiences rainy and dry seasons due to movement in and out of the ITCZ
• Natural causes of climate change

  • Volcanic eruptions
  • Asteroid collisions
  • Sunspot activity
  • Orbital changes
• Volcanic eruptions


  Release sulfur dioxide and ash, causing global cooling in the short-term
• Asteroid collisions


  Throw up dust, causing global cooling in the short-term
• Sunspot activity


  More sunspots = hotter sun = global warming/cooling over longer periods
• Orbital changes


  Changes in Earth's orbit and axis tilt cause global heating and cooling over very long periods
• Circular orbit


  Orbit around the sun where the distance to the sun is equal at any point
• Elliptical orbit


  Orbit around the sun where the distance to the sun varies, sometimes further away (cooler) and sometimes closer (hotter)
• Axis tilt


  • The planet's axis is not straight, it is on an angle and wobbles over a 41,000 year period
  • This puts the planet closer or further from the sun, impacting heating and cooling
• Ice cores contain trapped carbon dioxide, which indicates past climate conditions
• High CO2 in ice cores


  Indicates it was warmer in the past
• Low CO2 in ice cores

  Indicates it was colder in the past
• Tree rings


  • Narrow rings indicate a short growing season and colder temperatures
  • Wide rings indicate a long growing season and warmer temperatures
• Historical sources like old photographs, drawings, and written accounts are less reliable for determining past climate
• Satellite images are very reliable for determining current climate
• Greenhouse effect


  Greenhouse gases in the atmosphere trap outgoing long-wave radiation, causing the planet to heat up
• Some greenhouse gases are naturally occurring, but human activities are enhancing the greenhouse effect
• Thermal expansion


  As the oceans heat up, the water molecules expand, causing sea levels to rise
• Future climate change scenarios

  • Option C (best case): Low population growth, renewable energy, 30cm sea level rise
  • Option B (moderate): Lower population growth, some renewable energy, 1.5C warming
  • Option A (worst case): High population growth, fossil fuel use, 1m+ sea level rise
• Impacts of climate change

  • More frequent flooding
  • More frequent and stronger hurricanes/cyclones
  • Changes to farming and agriculture
• Tropical cyclones/hurricanes/typhoons


  Large rotating storms that form in the tropics, measured on the Saffir-Simpson scale from 1-5 based on wind speed
• Hazards of tropical cyclones

  • Strong winds
  • Storm surges
  • Coastal flooding
  • Intense rainfall
  • Landslides
• Formation of tropical cyclones

  1. Require warm ocean temperatures

  2. Coriolis effect to spin

  3. Often form over West Africa and move across the Atlantic
• Formation of hurricanes


  1. Warm water required

  2. Coriolis effect

  3. Storms form over West Africa

  4. Storms merge due to Coriolis effect

  5. Low wind shear in upper atmosphere required

  6. Sea surface temperatures of 27 degrees required

  7. Occurs over oceans

  8. Dissipates when hits land
• Hurricanes


  • Swirling winds and clouds due to Coriolis effect
  • Very low pressure, often below 1000 millibars
• Lower the pressure


  Stronger the winds
• Hurricanes have greater impacts in low-income countries compared to high-income countries
• Bangladesh


  • Very low-lying, only 2 metres above sea level
  • Located on a river delta
  • Coastal location
• Storm surges and heavy rainfall

  Cause flooding in Bangladesh