Climate Change & Global Warming (WJEC Eduqas GCSE Geography B): Revision Note

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The notes on this page cover parts 2.4.1 and 2.4.2 of the WJEC Eduqas GCSE B Geography.

2.4.1 How has the climate changed during the Quaternary period?

• An overview of how climate has changed to include glacial and inter-glacial periods.

2.4.2 What are the causes of global warming?

• Natural processes that create the greenhouse effect.

• Evidence for global warming, including the role of human activity as one contributory factor in global warming.

How has climate change since the Quaternary period?

• The global climate conditions of the Earth range 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 between 20,000 and 12,000 years ago

Global climate over time

Ice core data: changes in temperature over the last 11,000 years

• As well as the historical changes in climate, average temperatures have increased annually since the 1980s

Recent climate change

Natural processes leading to 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

• 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

Natural causes of the greenhouse effect

Milankovitch cycles

• Milankovitch cycles 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 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

• 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 

Evidence for global warming

The evidence for global warming comes from:

• Ice cores which trap ash, air bubbles and microbes

• Preserved pollen

• Historical sources such as diaries, art and weather records

• Tree rings

Recent evidence for climate change

• Recent evidence of global warming includes:

  • Glaciers reducing in size and melting ice: Arctic Sea ice is at an all-time low

  • Rising sea levels: 

    • Melting ice adds more water

    • Warm water expands in volume

  • Plant and tree flowering patterns are changing

  • Bird migration times have altered

  • Shorter hibernations

  • Bird nesting occurring earlier

Human activity and global warming

• Human activity is one contributory factor in global warming

• It is increasing the amount of certain 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

  • Methane, nitrous oxides and chlorofluorocarbons are also increasing

• 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^°C since pre-industrial times

Greenhouse gases from human activity

• Carbon dioxide (CO_₂)

  • Burning of fossil fuels – power stations, vehicles

  • Burning of wood

  • Deforestation - trees utilise CO_₂ in photosynthesis. The fewer trees there are, the less CO_₂ is removed from the atmosphere

• Methane (CH_₄)

  • Decay of organic matter – manure, waste in landfill, crops

  • Released by cattle and during rice cultivation

• Nitrous Oxide (N_₂O)

  • 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 CO_₂ 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 CO_{₂ –} 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 CO_₂.