Geography Climate and change

Geography Climate and change

1. Past climate change

   • The weather can change from minute to minute, however climate is defined as the average weather conditions over 30 years
   • Climate has changed a great deal in the past. We know this by
     • Fossils of animals and plants in regions they are not found in today
     • Evidence of glaciation in regions that are now free of ice
     • Evidence from rocks showing us the climate conditions when those rocks were formed
     • Evidence from ice cores in Greenland and Antarctica showing us how much carbon dioxide was in the atmosphere when the ice was formed
   • 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
     • 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

2. The causes of change

   • Volcanic eruptions
     • Large eruptions emit vast quantities of dust and gases such as sulphur dioxide into the atmosphere
       • This blocks out or absorbs incoming solar radiation so the earth cools
         • Examples include Mt Pinatubo in 1991, the Laki eruption in 1783 and Mt Toba 70,000 years ago
   • Large asteroid collisions have a similar cooling effect to volcanic eruptions, as they throw dust and ash into the atmosphere
   • Sunspot activity
     • sunspots are darker areas on the Sun's surface, they are signs of greater solar activity
       • There are long periods with very few sunspots such as 1645 - 1715 (coincides with the Little Ice Age)
   • Changes in the Earths orbit and rotation (Milankovitch mechanism)
     • The shape of the Earths orbit changes (becoming less circular) over a period of 100,000 years - known as orbital eccentricity
       • All these effects change the amount of solar energy received at the Earth's surface
     • The Earth "wobbles" on its axis over a period of 26,000 years - known as precession
     • The tilt of the axis varies between 21° and 24° over about 40,000 years

3. The little ice Age

   • Probably caused by reduced sunspot activity
   • It lasted from about 1300 to as late as 1870 and the average temperatures were at least 1°C below those of today
   • Impacts included:
     • The Baltic sea froze over in winter, as did most of the rivers in Europe including the thames
     • Sea ice, which at the moment is fat to the north, reached as far south as Iceland
     • 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
     • Remote areas were abandoned by settlers as survival was impossible. An example of this would be Greenland

4. The impact on Mega fauna

   • 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
     • During this period a number of large animals (mega fauna) disappeared completely (as many as 130 species in all)
       • Examples include giant beavers, mammoths and sabre tooth tigers
         • 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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