Climate and Climate Change

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Climate Records from the Vostok Ice Core Covering
the Last 420,000 Years (http//www.exploratorium.e
du/climate/cryosphere/data2.html )
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Reconstruction of Northern Hemisphere temperature
anomaly trend from 1000 A.D. to present IPCC
2001
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Earth surface temperature by year (red bars) and
decade (black line) (IPCC 2001)
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Recent Temperature Variation

• Mean global temperature now ca. 15C
• 135-125,000 yrs BP, warm interglacial (Sangamon)
• Cooling since Sangamon to minimum temperatures
  18,000 yrs BP (Wisconsin glacial maximum, 5-6 deg
  cooler than recent)
• Rapid warming 15,000-10,000 BP to current level,
  warmest recent temperatures 8,000-4,000 yrs BP
  (Hypsithermal, 0.5-1 deg warmer than recent)

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• Medieval warm period, 900-600 BP (0.1-0.2 deg
  warmer than recent)
• Little Ice Age, 550-150 BP (0.5-1 deg cooler than
  recent)
• 20th century global warming

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Concentrations of principal anthropogenic
greenhouse gases in the industrial era Hansen et
al., 1998 Hansen and Sato, 1999.
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Modern CO2 concentration in Earths atmosphere,
ppm (http//cdiac.esd.ornl.gov/)
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Other causes for climate change
Mount Pinatubo, June 13, 1991 (Image courtesy of
NOAA)
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Precipitation trends 1950-1999
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Some Conclusions Of2001 IPCC Report

• 20th C surface temperature increase of 0.6º C
  (1.1º F)
• 10 decrease in snow cover since 1960
• Precipitation has increased 0.5-1.0 per decade
• No 20th Century trend in frequency of severe
  storms
• No evidence of increase in tornadoes or
  thunderstorms in 20th C

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Global mean temperature change for 1/yr CO2
increase with subsequent stabilisation at 2xCO2
and 4cCO2. The red curves are from a coupled
AOGCM simulation (GFDL_R15_a) while the green
curves are from a simple illustrative model with
no exchange of energy with the deep ocean. (IPCC
2001)
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Climate model predictions of 21st C. temperatures
based on several scenarios of fossil fuel
consumption
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the IPCC-DDC scenario IS92a (GS greenhouse gases
and sulphate aerosols) for the years 2021 to 2050
relative to the period 1961 to 1990
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Major Uncertainties

• Rate of ocean heat uptake
• Magnitude (and long term direction) of marine and
  terrestrial carbon sources and sinks
• Feedback between warming, cloud cover, and
  planetary radiation balance
• Aerosol radiative properties