Natural & Enhanced Greenhouse Effect (Edexcel IGCSE Geography)

Changes in the Global Climate

• The global climate conditions of the Earth change over time, leading to colder and warmer periods
• The last 2.6 million years are the Quaternary period, during this, there have been 60 cold periods and warmer interglacial periods
• The last ice age ended approximately 25,000 years ago
• The evidence for these changes comes from:
  • Ice cores which trap ash, air bubbles and microbes
  • Preserved pollen
  • Historical sources such as diaries and art
  • Tree rings

Causes of Natural Climate Change

Cause	Impact
Milankovitch Cycles	Long-term changes to the Earth's orbit and position. This changes how much solar radiation the Earth receives The Earth's orbit changes every 100,000 years a more circular orbit leads to cooler periods and an elliptical orbit leads to warmer periods The Earth's tilt varies every 40,000 years and the greater the tilt the hotter the summers and the colder winters  Every 24,000 years, the Earth wobbles on its axis and this can affect the seasonal temperatures
Volcanic eruptions	Large-scale eruptions lead to vast quantities of ash being ejected into the atmosphere Ash in the atmosphere blocks solar radiation, leading to a decrease in temperatures
Sunspot activity	Increased sunspot activity is linked to higher average temperatures
Atmospheric dust	Asteroids and meteors entering the Earth's atmosphere may increase the amount of dust, which decreases temperatures

The Greenhouse Effect

• The greenhouse effect is essential to the survival of life on Earth:
  • Greenhouse gases in the atmosphere allow short-wave radiation from the sun through to the Earth's surface
  • This is absorbed by the atmosphere and Earth's surface and re-radiated as long-wave radiation
  • The greenhouse gases absorb some of the long-wave radiation (which we feel as heat)
    • They stop it from radiating out into space
  • This maintains the Earth's average temperature
  • Without the greenhouse effect, the average temperature would be -18^oC

Greenhouse Gases from Natural Sources  

• Water vapour - evaporation from the oceans/seas and plants
• Carbon dioxide - volcanic eruptions, wildfires and respiration
• Methane - emitted from oceans and soils as part of decomposition, termites also emit methane
• Nitrous oxide - soils and oceans

The Enhanced Greenhouse Effect

• Human activity is increasing the number of greenhouse gases in the atmosphere:
  • Carbon dioxide (CO₂) levels in the atmosphere have increased by more than 100 parts per million (ppm) to 420ppm in 2020
• Increased amounts of greenhouse gases have led to the enhanced greenhouse effect:
  • Less long-wave radiation (heat) can escape the atmosphere
  • Average global temperatures have increased over 1^oC since pre-industrial times

Average Global Temperatures

Human Sources of Greenhouse Gases

Greenhouse Gas	Sources from human activity
Carbon Dioxide (CO2)	Burning of fossil fuels - power stations, vehicles Burning of wood Deforestation - trees utilise CO2 in photosynthesis. The fewer trees there are the less CO2 is removed from the atmosphere
Methane (CH4)	Decay of organic matter - manure, waste in landfill, crops
Nitrous Oxide (N2O)	Artificial fertilisers Burning fossil fuels
Chlorofluorocarbons (CFCs)	Aerosols Refrigeration units Air conditioning