The greenhouse effect is a process through which greenhouse gases trap the radiation emitted by the

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Global warming
The greenhouse effect is a process through which
greenhouse gases trap the radiation emitted by
the Earths surface, resulting in global warming
SUN
3. Most infrared radiation escapes to outer
space and cools the Earth

4. Some infrared radiation is trapped by
greenhouse gases and reduces the cooling effect
1. Solar radiation passes through the atmosphere
and warms the Earths surface
5. Temperature is warmer as a result
2. Infrared radiation is given off by the Earth
Adapted from Defra (2005) Climate change and the
greenhouse effect a briefing from the Hadley
Centre
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CO2 levels are already unprecedented in the last
800,000 years
CO2 Concentration (ppmv)
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Projected concentrations of CO2 during the 21st
century are two to four times the pre-industrial
level
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The climate is changing temperature rise
Global average surface temperature increased over
the 20th Century by 0.7?C with particularly
strong warming (0.4oC) since the 1970s
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The climate is changing key indicators
Sea level rise
Global average sea levels rose between 0.1 and
0.2m during the 20th century.
Arctic sea ice declining at an unprecedented rate
summer extent is now declining by 8 per
decade, and in parts of the Arctic sea ice has
thinned by over 40 in the last 50 years. 2006
summer sea ice extent was the lowest ever
recorded.
Sea ice
Snow cover
Reduction of 10 in extent of snow cover in the
Northern Hemisphere mid- and high-latitudes since
the late 1960s
Reduction of extreme low, and increase in extreme
high, temperatures since 1950.
Increase in total rainfall by 0.5-1.0 per decade
in the 20th Century over most mid/high Northern
Hemisphere continents
Higher frequency and intensity in recent decades
over parts of Asia and Africa
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US impacts of Climate Change (Stern Review-Ch. 5)

• Geographical spread potential short-term
  benefits in the North and extensive damage
  possible in the South.
• Coastal flooding and extreme events
• short to medium term, most costly impacts.
• more powerful hurricanes raise risks along the
  Eastern seaboard and Gulf of Mexico.
• Defensive investment could be substantial.
• Snowfall/melt and water resources
• reduced snowfall and shorter winters will change
  snowmelt patterns
• Water supply affected along Pacific coast and
  California and the farmlands of the Mississippi
  basin whose western tributaries are fed by snow
  melt.

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US impacts of Climate Change (Stern Review-Ch.
5) - contd

• Agriculture
• up to 2 - 3ºC ( adaptation to shifting crop
  varieties and planting times). Overall Impacts on
  yields moderate (or even positive with a strong
  carbon fertilization effect) Assuming sufficient
  irrigation water in Southeast and Southern Great
  Plains
• Above 3ºC, total output could fall by 5 20
  even with effective adaptation because of summer
  drought and high temperatures.
• Farm production in general is expected to shift
  northwards.
• Rising Winter temperatures
• North lower energy bills and fewer cold-related
  deaths.
• South rising summer energy use for
  air-conditioning and refrigeration and more
  heat-related deaths.
• This rebalance of economic activity could also
  induce a northward population shift.

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Attribution Man-made (anthropogenic) factors
Natural factors only
Natural and man-made factors
Climate models demonstrate that natural factors
alone are not sufficient to explain the pattern
of global temperatures observed over the last 150
years
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The Importance of the US...
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Sources of greenhouse gases
Global Emissions 2000 41 GtCO2e 2005
- 45 GtCO2e

• The rising levels of greenhouse gases are driven
  by human emissions, primarily from fossil fuel
  burning (e.g. for heat and power generation),
  forest clearance and burning, and agriculture.
• US Emissions in 2000
• 6.5 GtCO2e (16 Global Emissions)
• 90-Energy
• 40 Electricity Heat
• 26 Transport

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