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Past Climate Change


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Past Climate Change

  1. 1. KEY IDEA Climate has changed in the past through natural causes, on timescales ranging from millions to hundreds of years AIM To recognise that the world’s climate has changed significantly over time
  2. 2. What do you already know about climate change? SNOWBALL!
  3. 3.
  4. 4. <ul><li>The distant past </li></ul><ul><li>At times in the past, huge ice sheets stretched from the North Pole as far south as London. Scientists know that climate was different in the past. They use physical evidence such as: </li></ul><ul><li>fossilised animals, plants and pollen that no longer live in the UK </li></ul><ul><li>Landforms, like the U shaped valleys left by retreating glaciers </li></ul><ul><li>samples from the ice sheets of Greenland and Antarctica </li></ul>
  5. 5. <ul><li>During the Quaternary (the last 2.6 million years of geological time), warm periods ( interglacials ) lasted for between 10,000 and 15,000 years. </li></ul><ul><li>Cold periods ( glacials ) lasted about 80,000-100,000 years. </li></ul><ul><li>During some glacial periods, it became so cold that the Earth plunged into an ice age. Huge ice sheets extended over the continents in the northern hemisphere. </li></ul><ul><li>There were also vast areas of floating sea ice. </li></ul><ul><li>The last time this happened was between 30,000 and 10,000 years ago, in the last ice age. </li></ul><ul><li>The ice sheets were 400-3000 metres thick, and so heavy that they made the Earth’s crust sag. </li></ul><ul><li>So much water was locked up in the ice sheets that sea levels fell by over 100 metres. </li></ul>
  6. 6. Ice sheets are like a time capsule. They contain layers of ice, oldest at the bottom, youngest at the top. Each layer is one year of snowfall. Trapped in the ice layers are air bubbles. These preserve air from the time the snow fell. Locked in the air bubble is carbon dioxide. Climatologists can reconstruct past temperatures by drilling a core through the ice and measuring trapped carbon dioxide in ice layers.
  7. 7. Al Gore explains global warming in 10 mins Watch the clip from An Inconvenient Truth. Note 5 key facts that Al Gore explains about our changing climate.
  8. 9. <ul><li>The recent past </li></ul><ul><li>There is also evidence for climate change in more recent times. Evidence comes from: </li></ul><ul><li>old photographs, drawings and paintings of the landscape </li></ul><ul><li>written records, such as diaries, books and newspapers </li></ul><ul><li>the recorded dates of regular events, such as harvests, the arrival of migrating birds and tree blossom </li></ul><ul><li>These sources are often not very accurate, because they were not intended to record climate. However, they can still give us some idea of overall climate trends in the recent past. This type of evidence suggests that climate changes regularly – every few hundred years. Average temperatures over the past 2000 years or so have probably varied between 1-1.5ºC colder or warmer than average temperatures today. </li></ul>
  9. 10. McCarty Glacier in Alaska
  10. 11. Greenland Ice Sheet melting
  11. 12. Larsen B ice shelf Loss of ice
  12. 13. Old photographs, paintings and drawings
  13. 14. Written records such as books and diaries
  14. 15. 1400s Sodium in ice, seas stormier, period of cooler temperatures Use the information from ‘Discovering Antarctica’ to annotate the diagram.
  15. 16. Exam-style question Describe some of the evidence that tell us that climate was different in the past. (4 marks)