Into the Greenhouse again

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Into the Greenhouse (again)

• The Earths average surface temp has warmed by
  0.6 oC
• Concentrations of CO2, CH4, and other greenhouse
  gasses have been increasing over the last 100
  years because of human activities
• Greenhouse gasses have contributed to global
  warming
• But how much??

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• Since 1850, greenhouse gasses have added 2.5 W/m2
  to the greenhouse effect
• CO2 accounts for 60 of greenhouse gasses

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• Since 1850, greenhouse gasses have added 2.5 W/m2
  to the greenhouse effect
• CO2 accounts for 60 of greenhouse gasses

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• What would the temperature be without added
  greenhouse gasses?

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Climate change on different timescales

• Tectonic timescale
• over last 50-100 million years, the Earths mean
  temperature has cooled by 5-10 oC
• Orbital timescales
• since the LGM (21,000 years ago)-6,000 years
  ago, the Earth has warmed 4-6 oC
• Since 6,000 years ago, the earth has cooled by
  lt1 oC
• Millennial timescales
• Temp decrease during the LIA of 0.2-0.25 oC
• Millennial scale changes (recent) unlikely to be
  more than 0.2 oC
• Decadal timescales
• ENSO, volcanoes, etc., not relevant to longer
  term temperature changes

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Timescales of climate change
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Climate change on different timescales

• Tectonic timescale
• over last 50-100 million years, the Earths mean
  temperature has cooled by 5-10 oC
• Orbital timescales
• since the LGM (21,000 years ago)-6,000 years
  ago, the Earth has warmed 4-6 oC
• Since 6,000 years ago, the earth has cooled by
  lt1 oC
• Millennial timescales
• Temp decrease during the LIA of 0.2-0.25 oC
• Millennial scale changes (recent) unlikely to be
  more than 0.2 oC
• Decadal timescales
• ENSO, volcanoes, etc., not relevant to longer
  term temperature changes

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Climate change over longer timescales the
mighty Vostok record
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Climate change on different timescales

• Tectonic timescale
• over last 50-100 million years, the Earths mean
  temperature has cooled by 5-10 oC
• Orbital timescales
• since the LGM (21,000 years ago)-6,000 years
  ago, the Earth has warmed 4-6 oC
• Since 6,000 years ago, the earth has cooled by
  lt1 oC
• Millennial timescales
• Temp decrease during the LIA of 0.2-0.25 oC
• Millennial scale changes (recent) unlikely to be
  more than 0.2 oC
• Decadal timescales
• ENSO, volcanoes, etc., not relevant to longer
  term temperature changes

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Climate change over the last 1000 years
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Climate change on different timescales

• Tectonic timescale
• over last 50-100 million years, the Earths mean
  temperature has cooled by 5-10 oC
• Orbital timescales
• since the LGM (21,000 years ago)-6,000 years
  ago, the Earth has warmed 4-6 oC
• Since 6,000 years ago, the earth has cooled by
  lt1 oC
• Millennial timescales
• Temp decrease during the LIA of 0.2-0.25 oC
• Millennial scale changes (recent) unlikely to be
  more than 0.2 oC
• Decadal timescales
• ENSO, volcanoes, etc., not relevant to longer
  term temperature changes

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Clue 1 Instrumental records show its getting
warmer

• The Earth's average near-surface atmospheric
  temperature has risen 0.6 0.2 Celsius (1.1
  0.4 Fahrenheit) in the 20th century.

Brohan, P. et al., 2006, J. Geophysical Research
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How responsive is climate to changes in CO2?
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Simulated warming with 2xCO2

• Why are estimates so varied?
• How much has CO2 changed in the past?
• What are the skeptics arguments, and what are the
  counter-arguments?
• READ chapter 18 and be prepared to discuss next
  week