Climate change

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Past climate change

Climate change is any significant change in the weather of a region over a period of several decades e.g. increasing average temperature

Evidence of past climate change:

  • Global temps fluctutated in past 1 million years (increase from 11 degrees to 15 currently)
  • There have been 4 interglacials and glacials
  • About 100,000 years ago we entered our current warm period (increase from 13 degrees to 15)
  • There are changes over time in the extremes of glacials and interglacials (during holoscene period temps may have been 2 degrees warmer than today)

These trends are based on levels of oxygen found in the GRIP ice cores in Greenland between 20,000 to 7000 years ago

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Global Warming

The recent gradual warming of the Earth's atmosphere since the 19th century onwards, largely believed to be the result of human activity.

Since 20th century Earth's surface temp has increased by 0.8 degrees C (Two thirds of change since 1980)

Recent rapid increase due to:

Increase in population-

  • More car usage
  • More energy needed so more fuels burnt
  • Increase in development leading to more heat output

Increased gasses in the atmosphere-

  • Less heat escaping the Earth (reflected back)
  • Deforestation leading to more abundance of CO2
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Evidence for current global warming

Instrumental readings:

  • Measured directly by thermometers meaning data is readily avaliable (however readings subjective and weather stations not widespread)

Glaciar retreat and shrinking:

  • Up to 25% of global mountain glaciers could disappear by 2050(Greenland and Antartica ice sheets shrinking with Greenlandlosing up to 250 cubic km per year 

Arctic ice cover:

  • Last 30 years Arctic ice has thinned to half its thickness (less ice means less solar radiation reflected so sea will absorb more increasing the rate of melting.

Sea level rise:

  • Sea level rise by average of 1.8mm per year over the last century with predicted 3mm increase per year in last 10 years
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Predicted future trends

The IPCC predicts global temp could rise from anything between 1.1 to 6.4 degrees by the end of the century 

There is a greater than 90% probability that the effect of human activity since 1750 has been to warm the planet 

Temperature increase since the mid 20th century is due to greenhouse gasses 

Hot extremes like heatwaves and heavy rain will continue to become more frequent 

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Greenhouse gasses in global warming

Water vapour:

  • Biggest natural contributor to greenhouse effect
  • Polar atmosphere contains very little water vapour 
  • Tropics have up to 4% water vapour 
  • Little influence from human factors 


  • Accounts for largest 'trace gas'
  • Responsible for 60% of enhanced GHE
  • CO2 stays in the atmosphere for about 100 years
  • Burning fossil fuels and deforestation increases CO2 levels
  • CO2 increases more in Northern hemisphere (increased by 40% since industrial revolution)


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Greenhouse gasses in global warming (cont)


  • Accounts for 20% of enhanced GHE 
  • Generated by bacteria during decay
  • Methane remains in stmosphere for 11-12 years
  • Two thirds comes from man made sources e.g. fossil fuels and fuel drilling 
  • Difficult to predict removal rate

Nitrous Oxide:

  • Extremely small concentration in atmosphere 1/1000 of CO2
  • 200-300x more effective at trapping heat than CO2
  • Last for 150 years in the atmosphere 
  • Main contributor belived to be widespread use of nitrogen fertiliser
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