Causes of Climate Change (Cambridge (CIE) IGCSE Geography) : Revision Note

Evidence of climate change

• 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, when there have been 60 cold periods and warmer interglacial periods

• The last ice age ended approximately 25,000 years ago

• Evidence that change happened:

  • Ice cores have trapped ash, air bubbles and microbes

  • Preserved pollen

  • Historical sources such as diaries and art

  • Tree rings

  • Sea ice position

• Over the last 200 years, we have had more accurate measurements of temperature

Factors affecting natural climate change

Milankovitch cycles

• These are 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 41,000 years and the greater the tilt, the hotter the summers and the colder the winters are

• 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 enhanced greenhouse effect

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 then radiated back into the atmosphere as long-wave radiation (heat)

  • The greenhouse gases absorb some of the long-wave radiation (heat) and stop it from radiating out into space

  • This maintains the Earth's average temperature

  • Without the greenhouse effect, the average temperature would be -18°C

Greenhouse gases from natural sources  

• Water vapour—evaporation from the oceans/seas and plants

• Carbon dioxide—volcanic eruptions, wildfires and respiration

• Methane is emitted from oceans and soils as part of decomposition; termites also emit methane

• Nitrous oxide—soils and oceans

• 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 420 ppm in 2020

The enhanced greenhouse effect

• Population growth has led to:

  • higher energy demand

  • greater food production

  • more industrialisation

  • increased transport

• All of these are increasing the proportions of greenhouse gases in the atmosphere

• This has led to the enhanced greenhouse effect:

  • Less long-wave radiation (heat) can escape the atmosphere

  • Average global temperatures have increased over 1°C since pre-industrial times

Greenhouse gases from human activity

• Carbon Dioxide (CO₂) - the burning of fossil fuels, burning of wood and deforestation (less CO₂ is removed from the atmosphere)

• Methane (CH₄)—decaying organic matter, including manure and waste in landfills, rice fields and livestock

• Nitrous Oxide (N₂O)—artificial fertilisers and burning of fossil fuels

• Chlorofluorocarbons (CFCs)—aerosols, refrigeration, air conditioning