Causes of Climate Change (OCR GCSE Geography)

Natural 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
  • 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: Emitted from oceans and soils as part of decomposition, termites also emit methane
• Nitrous oxide: Soils and oceans

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 summers are and 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	Sunspots are dark spots appearing on the sun's surface Increased sunspot activity is linked to higher average temperatures as the sunspots indicate that the sun's effectiveness at radiating heat is increased The IPCC state the role of sunspots in climate change is minimal
Atmospheric dust	Asteroids and meteors entering the Earth's atmosphere may increase the amount of dust which decreases temperatures

The Greenhouse Effect

The natural and enhanced greenhouse effect

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 Released by cattle and during rice cultivation
Nitrous Oxide (N2O)	Artificial fertilisers Burning fossil fuels
Chlorofluorocarbons (CFCs)	Aerosols Refrigeration units Air conditioning

Fossil fuels 

• Fossil fuels account for almost 50% of global greenhouse gas emissions
• Fossil fuels are used in transportation, construction, heating, manufacturing, and energy production 

Agriculture

• Deforestation to clear land for grazing and crops leads to less CO₂ being absorbed during photosynthesis
• The production of fertilisers and pesticides uses fossil fuels
• Increased raising of dairy and beef cattle as well as rice cultivation increases methane emissions
• Artificial fertilisers also increase the amount of nitrogen oxide released into the atmosphere

Construction 

•  The manufacture of cement releases CO₂ - it is made from limestone which contains carbon

Transport

• The increasing global population has led to increased numbers of cars, lorries, and planes
• Most transport uses petrol/diesel which comes from oil as fuel this releases CO₂