Changes in the Global Climate (Edexcel GCSE Geography A)

Changes in the Global Climate

• Climate change is large-scale, long-term changes in average temperatures and weather patterns

• 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

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

Temperatures continue to rise year on year 

The greenhouse effect

• The greenhouse effect is essential to the survival of life on Earth

  • Greenhouse gases in the atmosphere allow thermal radiation from the sun to reach the Earth's surface

  • These greenhouse gases absorb some of the thermal 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

The greenhouse effect

Causes & Evidence of Natural Climate Change

Causes of Natural Climate Change

Milankovitch cycles

The shape, tilt and wobble of Earth's movement over thousands of years affect long-term climate

Volcanic eruptions

Large-scale eruptions block insolation and reduce temperatures

Ejection of solar plasma from the Sun

Photo by NASA on Unsplash

The more 'spots' on the Sun's surface, the higher the Sun's output

Photo by The Adaptive on Unsplash

Evidence of natural climate change

• The evidence for the natural changes comes from a range of sources

Ice cores 

• These trap ash, air bubbles, and microbes

  • The air bubbles contain CO₂, providing information about past temperatures

  • Ice cores give information regarding the climate for the last 2.6 million years

Handling an ice-core

Ice-cores are drilled and stored in large freezers, ready to be examined

Preserved pollen

• Sediment cores taken from peat bogs and lake beds may contain preserved pollen

• Looking under a microscope, it is possible to identify which plant it came from

• Scientists then work out which climatic conditions were needed for the plant to grow and where they grew

Pollen under a microscope

Pollen viewed under a microscope shows the types of flowers that grew in the past

Historical sources 

• Historical paintings, books, newspapers and diaries provide evidence of what the climate used to be like 

  • Records of agricultural reports show what crop yields were like

  • The Met Office has collected weather conditions going back as far as 1861

  • Photographic records show how glaciers have retreated

  • Paintings such as the frost fairs on the Thames in London in the 19th Century

  • Diaries kept by people such as a gentleman farmer from North-West England dating back to 1815

  • Books by authors such as Charles Dickens and Sir Arthur Conan Doyle 

• These are subjective and so may be inaccurate

The frost fair in full swing. Photo: Wikicommons

Tree rings

• Fossilized tree remains enable scientists to examine the climate over thousands of years

• The study of tree rings is called dendrochronology

• Each year, a new tree ring is formed

• During good growing conditions, such as warmer and wetter years, trees grow more and so the rings are thicker

• If the rings are narrow and close together, there is less growth, indicating a cooler period 

Tree growth

Tree rings can show past climate conditions