Geography Climate and change

Past climate change
1. The weather can change from minute to minute, however climate is defined as the average weather conditions over 30 years
2. Climate has changed a great deal in the past. We know this by
  1. Fossils of animals and plants in regions they are not found in today
  2. Evidence of glaciation in regions that are now free of ice
  3. Evidence from rocks showing us the climate conditions when those rocks were formed
  4. Evidence from ice cores in Greenland and Antarctica showing us how much carbon dioxide was in the atmosphere when the ice was formed
3. In a period called the quaternary, there was a regular pattern of high and low temperatures. There was ice sheets covering much of Europe, Asia and North America
  2. In historical times temperatures have varied by as much as 1.5°C each side of the average. This can make a huge difference as it may only take this for new plants to grow in different areas
The causes of change
1. Volcanic eruptions
  1. Large eruptions emit vast quantities of dust and gases such as sulphur dioxide into the atmosphere
    1. This blocks out or absorbs incoming solar radiation so the earth cools
      1. Examples include Mt Pinatubo in 1991, the Laki eruption in 1783 and Mt Toba 70,000 years ago
2. Large asteroid collisions have a similar cooling effect to volcanic eruptions, as they throw dust and ash into the atmosphere
3. Sunspot activity
  1. sunspots are darker areas on the Sun's surface, they are signs of greater solar activity
    1. There are long periods with very few sunspots such as 1645 - 1715 (coincides with the Little Ice Age)
4. Changes in the Earths orbit and rotation (Milankovitch mechanism)
  1. The shape of the Earths orbit changes (becoming less circular) over a period of 100,000 years - known as orbital eccentricity
    1. All these effects change the amount of solar energy received at the Earth's surface
  2. The Earth "wobbles" on its axis over a period of 26,000 years - known as precession
  3. The tilt of the axis varies between 21° and 24° over about 40,000 years
The little ice Age
1. Probably caused by reduced sunspot activity
2. It lasted from about 1300 to as late as 1870 and the average temperatures were at least 1°C below those of today
3. Impacts included:
  1. The Baltic sea froze over in winter, as did most of the rivers in Europe including the thames
  2. Sea ice, which at the moment is fat to the north, reached as far south as Iceland
  3. Winters were much colder and longer, reducing the growing season by several weeks, the conditions led to widespread crop failure and the price of grain increased causing social unrest
  4. Remote areas were abandoned by settlers as survival was impossible. An example of this would be Greenland
The impact on Mega fauna
1. The climate change associated with the end of the ice age 10,000 - 15,000 years saw temperature rise by as much as 5°C in a very short period (by geological standard) of 1000 years
  1. During this period a number of large animals (mega fauna) disappeared completely (as many as 130 species in all)
    1. Examples include giant beavers, mammoths and sabre tooth tigers
      1. This is an example of a mass extinction event
        There have been many of these events in the past, often related to climate change

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Geography Climate and change

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