Unit 2 topic 4

• Greenhouse effect


  The influence that gases in the Earth's atmosphere have on trapping and freeing heat energy and radiation
• Global warming


  The changing climate and temperature patterns in the last 100-150 years
• Climate change


  The changing climate over a long period of time
• Greenhouse effect


  1. The Sun gives out light

  2. Light travels to the Earth

  3. The ground absorbs the light from the Sun

  4. Some light is reflected into space

  5. Some light is converted to heat and rises off the ground

  6. Some heat escapes into space

  7. Lots of heat is reflected (bounced) back onto the Earth
• Enhanced greenhouse effect


  Human activity is leading to an increase in the greenhouse effect, speeding up global temperature increase and causing various impacts
• While we need the greenhouse effect to work to some extent, too many greenhouse gases in the air will increase global temperatures too far
• Proxy records


  • Ice cores
  • Ocean sediments
  • Tree ring data (dendrochronology)
• Since 1900, global temperatures have increased by an average of 1 degree
• Because of the temperature increase, sea levels have risen by 19cm due to all the melting ice in the north and south poles
• Antarctica (South Pole) loses 134 billion tonnes of ice every year, and Greenland (Part of the North Pole) loses 287 billion tonnes
• The Earth is 4.5 billion years old; however, we only have records from 1850
• Glaciers around the world are shrinking and retreating. It is estimated that some may disappear entirely by 2035
• Arctic sea ice has thinned by 65% since 1975
• Human causes of climate change


  • Fossil fuels
  • Agriculture
• Natural causes of climate change


  • Solar activity
  • Deforestation
  • Orbital change
  • Volcanic eruptions

  
• Milankovitch cycles


  • Eccentricity
  • Axial tilt
  • Precession
• In 1991, Mount Pinatubo erupted, and the climate was colder around the globe in 1992
• Following Mount Pinatubo's eruption, global temperatures dropped by approximately 0.5 °C
• Socioeconomic impacts of climate change


  • Increased death due to increased heat
  • More extreme weather - more has to be spent on protection, prediction, rebuilding
  • Food prices increase due to a lack of food
  • Malnutrition and starvation due to a lack of food
  • Difficulties farming – due to lack of rain
  • Issues with water availability due to droughts
  • Increase in migration as people leave inhabitable areas
  • Low-lying coastal areas may flood, making people homeless (e.g., Maldives)
  • Some areas become inhabitable due to becoming so hot and dry
• Environmental impacts of climate change


  • Glaciers and ice sheets like Greenland shrink
  • This will lead to increases in sea levels
  • Other animals and plants have become extinct due to the changes
  • Some species are now found in higher latitudes due to increasing temperatures, e.g., butterflies, mosquitoes
  • Precipitation patterns will change – some areas will get more – some will get less
  • Species decline due to warming – e.g., coral is suffering from bleaching due to higher sea temperatures
  • Some coastal areas will be submerged – destroying habitat
  • Increased coastal erosion due to increased sea levels
  • Polar habitats will be reduced for animals like polar bears and penguins
• Microclimate


  Small-scale variations in temperature, precipitation, humidity, wind speed and evaporation
• Urban heat island effect


  A city experiences warmer temperatures than nearby rural areas
• Factors that influence urban climate


  • Building materials
  • Road surfaces
  • Cars and transport
  • Technology
  • Shelter from buildings
  • Reflective surfaces
• The mean winter temperatures are 1-2 degrees Celsius higher in urban areas compared to rural areas
• The mean summer temperature may be 5 degrees Celsius higher than in surrounding rural areas
• Evening storms frequently strike southern cities in the summer, bringing thunder, lightning, and heavy rain
• The confluence of cities and storms may not be a coincidence: more rain falls downwind in some major urban areas than in the surrounding countryside
• Urban areas


  • Tall buildings and a generally rougher land surface affect air flow, altering the course of the wind and producing turbulence
  • Increased shelter from buildings can increase the temperatures and cause significant issues with wind channelling
• Reflective surfaces


  • Reflection of solar radiation by glass buildings and windows
  • Central business districts of some urban areas can have high albedo rates (proportion of light reflected) that heats the area
• Mean winter temperatures are 1-2 degrees Celsius higher in urban areas compared to rural areas
• Mean summer temperature may be 5 degrees Celsius higher in urban areas than in surrounding rural areas
• Urban precipitation


  • Evening storms frequently strike southern cities in the summer, bringing thunder, lightning, and heavy rain
  • More rain falls downwind in some major urban areas than in the countryside
  • In the UK, urban areas are thought to increase the amount of precipitation over the UK by as much as 30 per cent
  • The number of rainy days is increased by 10 per cent, although snow and hail days are reduced by 14 per cent
  • The amount of fog experienced in the UK is doubled
• Reason 1 for increased urban precipitation

  1. The Urban Boundary Layer (UBL) creates a dome of rising warm air and low pressure

  2. As ground surfaces are heated, rapid evapotranspiration takes place, which can result in cumulus cloud and convectional weather patterns

  
• Reason 2 for increased urban precipitation

  Convergence - surface winds are drawn in from the surrounding rural fringe and this air then converges as it is forced to rise over the high urban canopy
• Reason 3 for increased urban precipitation


  1. The movement of winds contributes to increased rainfall patterns over the city that are most pronounced on the leeward side (away from the wind) of the city core

  2. Friction from the urban boundary essentially creates a rainfall process similar to a mountain barrier (air forced to rise, cool, condense and form clouds)

  3. As air passes over the urban area, it begins to sink, leading to lower precipitation in the leeward rural area
• Reason 4 for increased urban precipitation


  1. Fine particulates from pollution increase the number of condensation nuclei - clouds form as water vapour is attracted to condensation nuclei or hygroscopic nuclei in the atmosphere

  2. Precipitation is also thought to be raised in urban areas by air pollution (such as increasing smog and fogs)
• Smog


  Airborne pollution which may obscure vision, caused by small particles of material which become concentrated in the air
• Photochemical smog


  A specific type of air pollution caused by reactions between sunlight and atmospheric pollutants such as hydrocarbons and nitrogen dioxide
• Formation of photochemical smog


  1. Nitrogen dioxide and various hydrocarbons produced through combustion will interact with sunlight to break down into hazardous chemicals

  2. Primary pollutants (e.g. sulphur dioxide, carbon monoxide, volatile organic compounds) interact with the Sun to form secondary pollutants like ozone and additional hydrocarbons

  
• Urban wind


  • Urban wind speeds are thought to be lowered by the friction and barrier of the urban canopy
  • Buildings exert a powerful frictional drag on air moving over and around them, creating turbulence and rapid changes in wind direction and speed
  • Under intense heating, strong convectional processes form low-pressure thermals over cities that can draw in strong localised winds