Hazardous Earth

• Atmospheric Pressure


  Air pressure is the weight of the air. It can have a big impact on the type of weather on an area
• High Pressure system


  • Cool air sinks back down to the earth. The weight of the sinking air causes more pressure on the earth – so high pressure is formed
• Regular areas with high pressure

  • Arid areas (deserts). They usually receive low average rainfall (usually 250mm in a year)
• Low pressure system


  • The warmth of the earth's surface heats the air above. Air begins to rise – so there is less pressure on the ground below. As air rises it cools in the upper atmosphere and condenses forming clouds
• Regular areas with low pressure

  • Rainforest ecosystems are found in these areas
• Weather in high pressure areas

  • Clear skies – no clouds
  • Dry – no clouds for rainfall
  • Hot in summer/cold in winter
  • No/gentle winds
• Weather in low pressure areas

  • Clouds form
  • Wet – lots of rainfall (sometimes really heavy)
  • Hot in summer/cold in winter
  • No/gentle winds
• Regular high pressure causes mid-latitude areas to become

  Arid (meaning they receive low average rainfall)
• There are 2 reasons for mid-latitude areas becoming arid:
• The sun's rays are intense here and the clear skies mean daytime temperatures are high
• When sinking dry air reaches the surface it blows outwards blocking moist winds from the sea
• Areas with regular rainfall are often associated with the ITCZ. The ITCZ occurs near the equator where the two Hadley cells meet
• Here the suns rays are the most intense causing convectional rainfall to happen daily
• In these areas rainforest biomes occur, this is because it's warm and wet (perfect growing conditions)
• Because the earth is tilted the ITCZ moves northwards and southwards through the year taking heavy rain with it
• The Global Atmosphere


  • The Earth's atmosphere is constantly moving, the wind movements forma clear global circulation pattern
• The diagram below shows what happens when the two Hadley cells meet. The highest rainfalls are associated with this area
• ITCZ (Inter-Tropical Convergence Zone)


  This is an area of permanent low pressure. It occurs near the equator. The sun's radiation is highest here and so will cause the air to warm and rise quickly
• As it rises (low pressure) it quickly cools and condenses forming thunderclouds (cumulonimbus clouds)
• Rainfall in this area is heavy and regular (especially over land)
• The diagram to the left shows how high and low pressure systems operate on a global scale
• The movement of the air is controlled by the heating and cooling of air (driven by the sun)
• The area which receives the highest solar radiation is the equator
• The area which receives the lowest solar radiation are the poles (north and south)
• Air circulates as cells – air does not move into different cells
• There are three north and south of the equator. Air flows from an area of high pressure to low pressure as wind, rises at the area of low pressure and sinks down again to form an area of high pressure. This movement creates trade winds
• Climate change


  The average climate conditions of the planet. They vary over time. The earth has a history of going between warm (interglacials) and cold (glacial) periods
• Climate change can be caused by both natural events and humans
• Natural causes of climate change

  • Milankovitch Cycles
  • Solar Variation
  • Volcanism
  • Surface impact
• Milankovitch Cycles


  Natural changes to the earth's orbit and position that affect how much solar radiation we receive from the sun
• Effects of Milankovitch Cycles

  • Eccentricity – The orbit becomes elliptical so at times the earth is further from the sun causing it to be much cooler
  • Axial tilt – The angle of the earth's tilt changes so summers and winters are more extreme when this happens
  • Precession – The earth sometimes wobbles on it's axis and it changes seasons slightly
• Solar Variation


  The amount of radiation the sun produces varies over time. Lower solar activity are likely to end in glacials
• Volcanism


  Large-scale eruptions can lead to lots of ash in the atmosphere, sometimes it's so great it can block out the sunlight reducing global temperatures
• Surface impact


  Asteroids and comets can impact the earth's surface and cause lots of ash blocking out sunlight and reducing global temperatures
• Evidence of natural climate change

  • Historical Sources: Historical documents such as diaries, paintings etc can describe what the climate is like at the time
  • Tree rings: As trees grow they produce growth rings. In warmer climates growth rings are further apart. In cooler climates they are closer together
  • Ice Cores: Ice sheets in Greenland or Antarctica has built up over many years. In some places ice can be 3,000m deep. As snow falls and compacts as ice, it traps air bubbles – these contain a sample of what the atmosphere was like at that time
• Human causes of climate change

  • Transport
  • Energy
  • Industry
  • Farming
• The Greenhouse effect


  This is a natural process, which keeps the earth warm. Greenhouse gases (carbon dioxide, methane, nitrogen) trap some of the heat that is radiated from the surface which would have been lost into space. Without this the temperature of the earth would be a lot cooler
• The enhanced greenhouse Effect


  Human activity has resulted in an increased amount of greenhouse gases in the atmosphere. This means the earth absorbs more solar radiation and less radiation is able to escape – this causes an increase in temperatures
• Evidence of climate change

  • Sea Level Change
  • Warmer Global temperatures
  • Warmer Global temperatures and Carbon Dioxide
  • Melting Ice Caps
• Sea Level Change


  Long-term measurement of sea levels shows there has been 20cm increase since 1900. Rises have increased recently to 3.2mm per year and are more in some areas