Climate change  causes
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Climate change causes



Causes of climate change for Edexcel A Level Geography Spec

Causes of climate change for Edexcel A Level Geography Spec



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Climate change  causes Climate change causes Presentation Transcript

  • World at riskClimate change and its causes
    AS Geography
  • Climate change
    • Climate change can be assessed across short, medium and long timescales.
    • Short-term (recent) climate change is on a timescale of decades, e.g. global warming.
    • The medium-term (historical) timescale covers changes over the last few thousand years.
    • Long-term climate change has occurred on geological timescales, over hundreds of thousands to millions of years.
  • Geological timescales
    Atmospheric carbon dioxide concentration measured from the Vostok ice core, East Antarctica
  • Geological timescales
    • Ice cores, pollen analysis and past sea-level changes all indicate that climate has changed in the past.
    • Ice ages and interglacial's (warmer periods) seem to occur on a cycle of about 100,000 years.
    • The last ice age (the Devensian) ended approximately 10,000 years ago and the current interglacial period (the Holocene) began.
  • Historical climate change
    • Written records, pictures, tree rings and the extent of glaciers suggest climate has changed on historical timescales.
    • During the Little Ice Age (1400–1850) the climate was around 1C colder than it was in the twentieth century.
    • During the Medieval Warm Period (800–1400) the climate was around 1C warmer than in the twentieth century.
  • Recent climate change
    Global temperatures, 1850–2008
  • Recent climate change
    • Global temperatures fluctuated considerably between 1860 and 1970 (see graph on previous slide).
    • Since the late 1970s there has been a marked warming of around 0.5C.
    • This corresponds to the ‘era of global warming’.
    • Accurate instrumental measurements of air and ocean temperatures as well as ice cover testify to this record of global warming.
    • Increasingly ecosystems are changing in response to rising temperatures.
  • Possible causes of climate change
  • The greenhouse effect
    The greenhouse effect
    • The greenhouse effect is the natural process whereby gases in the atmosphere, principally carbon dioxide, trap some outgoing solar radiation.
    • This process warms the planet.
  • The enhanced greenhouse effect
    • Gases released by burning fossil fuels have enhanced the greenhouse effect and made it more powerful.
    • This has a net warming effect.
    • The level of carbon dioxide in the atmosphere has risen steadily since accurate recording began in the 1950s.
    Carbon dioxide concentrations, Hawaii, 1959–2005
  • Anthropogenic greenhouse gas sources
    • Transport, industry, electricity and heat account for over 50% of all greenhouse gas emissions.
    • Carbon dioxide is the most important greenhouse gas by volume.
    • Methane is a more powerful greenhouse gas per molecule.
    Global greenhouse gas emissions by economic sector, 2000
  • Anthropogenic greenhouse gas sources
    • The average carbon footprint in the developed world is five to ten times greater than in the developing world.
    • This confirms that global warming is a problem created largely by the developed world.
    Greenhouse gas emissions per person (tonnes of carbon dioxide equivalent, 2005)
  • Unprecedented global warming?
    Concern about global warming centres on key data, which are increasingly taken to be ‘fact’ by the majority of scientists:
    • Average global temperatures have risen by 0.8 C since 1880.
    • The decades from 1980–2000 were the hottest for at least 400 years.
    • Measured warming in the Arctic is twice that for the rest of the world.
    • Arctic sea ice in 2007 was at its lowest recorded extent.
    • Carbon dioxide levels, at 380 ppm in 2007, are over 100 ppm higher than pre-industrial ‘natural’ levels.