Evidence for climate change

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  • Created by: keeels
  • Created on: 08-05-14 16:55
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  • Evidence for Climate Change
    • Climate change is any significant change in weather of a region over a period of at least several decades,
      • Increasing average temperature or rainfall, or a change in the usual wind direction
    • Long-term climate change
      • Taking temperature as an indicator of climate, there have been huge changes over Earth's history - temperatures have been much higher at some points in the past than they are today
      • The data from the last 400,000 years shows flucations
      • Climate has shifted from cold glacial periods that last around 100,000 years and warmer interglacial periods that lasted around 10,000 years.
        • we're in an interglacial period now
    • Medium term climate change
      • The last glacial period ended about 18,000 years ago
      • The warming of the climate after this was fast at times, but it wasnt constant - about 13,000 years ago that the climate switched back to cooler conditions for about 1000 years
      • Around 5000 years ago, temperatures were higher by 1-2 degrees than today
    • Short- term climate change
      • Global warming is the term used for the rapidly increasing global temperature over the last century - there's been a sharp rise in temperature when you loock at the last 1000 years
      • The overall pattern over the last century shows a general increase in temperature, but the pattern hasn't been constant
      • Global temperatures rose steadily from the early 20th century until the 1940s (although they fluctuated annually), then dropped back down. Scientists thought there would be another glacial period, but temperatures have risen rapidly again since the 1970s (this is global warming)
    • Long Term change evidence
      • Ice cores
        • Scientists drill deep into ice sheets (huge masses of ice) to extract cores of ice. Ice sheets are made up of layers of ice - one layer is formed every year. So the ice at the bottom of the core is really, really old.
        • They can analyse the gases trapped when the ice formed to tell what the temperature was each year. Then they can figure out how temperature has changed over time
        • E.g a core has been extracted from the Antarctic ice sheet to a depth of 3000m and has been used to show temperatures for the last 400,000 years
      • Pollen analysis
        • pollen from plants is often preserved in sediment
        • The preserved pollen can be identified and dated to show when it was released
        • Scientists know the conditions that plants live in now. When they find preserved pollen from similar plants, it indicates that conditions were similar when that pollen was produced
      • Sea level change
        • sea level is affected by things like the volume of water stored as ice
        • Past sea levels are shown by raised beaches (formed when sea levels were higher) Raised beaches can be dated. They indicate that less water was stored as ice (i.e it was warmer)
    • Medium term change
      • Historical records
        • Historical records can indirectly indicate different conditions in the past. E.g agricultural reports (such as harvest times)  show changing conditions throughout human history.
      • Tree rings
        • A new tree ring is formed each year as a tree grows. If conditions that year were good, the tree ring produced will be thick
        • scientists can take cores and count the rings to find the age of a tree. They then look at the thickness of each ring to see what the climate was like each year
        • Tree rings can reliably show and date climate conditions up to 10,000 years ago
      • Retreating glaciers
        • Scientists can tell how big a glacier was and how far it extended by looking at the position of rocks deposited by it. These rocks can be dated to show when they were deposited
        • The distance of the rocks from the current glacier indicates climate change. E.g if the front of the glacier is now miles away from the rocks it indicates that temperatures have increased over that period of time
    • Short term changes
      • Weather records
        • Details of weather conditions have been consistently collected since 1861
        • These can be used to show detailed climate change over the short period they've been collected
      • Polar ice melt
        • Current research into the behaviour of polar ice shows a reduction in the amount of ice at both poles
        • Changes in the extent of polar ice shows changes in the climatic factors affecting them, e.g increased melting shows increased temperatures
      • Ecosystems changes
        • Changes in temperature affect the availability of food and shelter. This affects what species live in an area. So scientists can use changes in how species are distributed to indicate changes in the climate


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