Geography - Challenges for the planet

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1. How and why climate has changed since the last ice age.

Climate change

  • Since the end of the last ice-age, temperatures have increased by 6oC. Over this period there have been fluctuations with a series of warmer and colder periods. Between 800 and 1200AD there was a warm period followed by the Little Ice Age during the 16th and 17th century. For the past 100 years there has been a gradual increase in temperature, however temperatures have risen rapidly since 1960 and it is predicted that by 2100 temperatures will be 5oC warmer than now.

Volcanic activity

  • Volcanic dust puts huge amounts of ash and sulphur dioxide in the atmosphere. This acts to block solar radiation and therefore can cause a drop in temperatures.

e.g.

  • In 1815 mt tambora erupted, the following year was unusually cold and was called the 'year without a summer'

Orbital geometry (Milankovitch cycles)

  • Eccentricity: The earth's orbit of the sun varies in shape approximately every 100,000 years from a near circular orbit to an elliptical one. When there has been a circular orbit, glacial periods have occurred with warmer periods coinciding with more elliptical orbits.

  • Axial tilt: The tilt of the earth's axis also varies over time (21.5-24.5). Regions in the extreme upper and lower hemispheres will experience the hottest summers and the coldest winters during a maximum tilt.

  • Precession: Aside from the tilt, the axis also wobbles like a top. A complete wobble cycle is more or less 26,000 years. This motion is caused by tidal forces from the Sun and Moon.

Solar output

  • If the solar output changes by 1% then global temperatures can change by 0.5-1 degrees.

  • Also scientists have regularly counted the number of dark patches on the face of the Sun. These ‘sunspots’ are caused by intense magnetic activity in the Sun’s interior. More sunspots mean the Sun is more active and giving off more energy, so sunspot numbers are a ‘proxy’ for solar output.

2. The causes of current climate change on a local and global scale, including the burning of fossil fuels and the increase of methane in the atmosphere.

  • Burning fossil fuels - releases 25% of all CO2 emissions and we know this is one of the main greenhouse gases. the demand for energy from fossil fuels has increased (75% of china’s energy is from coal) because of higher demand for a better quality of life in developing countries and increase numbers of cars. This increased demand has meant that tonnes and tonnes of CO2 and other greenhouse gases have been emitted which is warming our planet.

  • Methane is a greenhouse gas which can trap heat within the atmosphere. Methane comes from organisms which were alive many years ago, recently dead rotting organisms and those alive today. Modern sources of methane include wetlands/swamps, paddy fields growing rice, landfills which contain rotting vegetable matter and the bowels of animals. The levels of methane in the atmosphere have been rising by 1.5% a year for

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