What we wish to learn Today:

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What we wish to learn Today
Climate Models

1. How has the climate changed during the recent
   past?
2. What can we say about current climate change?
3. How do climate models work and what are their
   predictions for the future?

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Possible Causes of Climate Change

• Long-Term
• Solar Luminosity
• Shifting Continents
• Greenhouse gases

• Medium-Term
• Orbital parameters
• Greenhouse gases

• Short-Term
• Oceans
• Sunspots
• Volcanoes
• Greenhouse gases

Power 4 x 1026 W 2 x 1017 W
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Causes of Climate change
A. Tectonic
C. Oceans / GHG
B. Orbital
D. ??
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Recent Trends in Temperature
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Solar Activity and Climate

• Maunder Minimum Very few sunspots were seen
  between 1645 and 1715
• Corresponds to the time of the Little Ace Age

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BUT, Change in sunspot number is greater than
change in solar radiation. The change in solar
radiation is only about 0.1, too small to
account for the full temperature shifts an
ongoing investigation
Sunspots and measured solar radiation
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Ash on cars
Pre-1991
Post-1991
VOLCANO !
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Volcanic eruptions cool global temperature
Volcanoes spew out 160x less CO2 than humans do
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Effects of El Niño and volcanoes on air
temperatures
Satellite troposphere temperature data
97-98 El Niño
El Niño index
El Niño effect on temperature
Satellite data minus El Niño effect
Residual Trend 0.11C per decade
Volcano effect on temperature
Pinatubo
After removing El Niño and volcanoes
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Summary of Climate Forcingsin energy terms of
Watts per m2

• Orbital variations
• 0.5 W m-2 / century (occurs over long
  time scales)
• Solar variation
• 0.29 W m-2 peak-to-peak over 2
  centuries
• Greenhouse Gases - past
• 0.0067 W m-2 / century CO2, 4050 BC
  to 1000 AD
• 0.0016 W m-2 / century CH4, 4050 BC
  to 1500 AD
• 0.0006 W m-2 / century N2O, 4050 BC
  to 1000 BC
• Volcanic eruptions
• 0 down to -10 W m-2, but short lived (a
  few years).
• Estimated long-term mean forcing -0.3 W m-2
  

Current GHG emission Doubling of CO2 4 W
m-2 !
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Past and Modern Changes on Earth
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Global distribution of CO2, 1992-2001
N. Hemisphere
S. Hemisphere
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Global distribution of CH4, 1992-2001
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Atmospheric CO2 concentration and temperature
are correlated in the Vostok ice core
15
Paleoclimate provides perspective on where we are
headed
Global Temperature (C)
IPCC Projections to 2100
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USING MODELS TO PREDICT CLIMATE

• Types of Models
• Physical Models (a desktop globe)
• Statistical Models (a regression, ymxb)
• Conceptual Models (a flow chart)
• Computer Models (Global Climate Models, GCMs)

Climate models are only sophisticated tools, not
crystal balls A useful model is not the one
which is true, but the one that is
informative all models are wrong, some are
useful
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What goes into a climate model?
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Climate change is not just an environmental
issue
INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE (IPCC)
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The models must use scenarios of future GHG
emissions
There are many different storylines
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Pick your future
Source IPCC TAR 2001
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Climate models work pretty well
Rainfall annual
Which is observed and which is modeled ?
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but there is some variation Prediction of the
1997-1998 El Nino by 6 different GCM models
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Models show that anthropogenic causes of
temperature change explain what has already
occurred.
Courtesy W. Washington/NCAR
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Predictions of large climate changes even by the
2050s
Hadley Centre for Climate Prediction and Research
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But, we control our destiny -- Temperature from
the present day to the 2080s
Hadley Centre for Climate Prediction and Research
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Take Home Message Prediction is Difficult,
Especially into the future
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Summary

1. Recent changes in Earth's paleoclimate record are
   likely due to shifts in ocean circulation, and
   the effects of greenhouse gas increases. 
   Volcanoes have had only a small effect, and the
   sun spot record cannot account for the heat input
   needed.
2. Temperature changes and greenhouse gas abundances
   are correlated. Rapid global warming is underway
   and models have been developed to predict the
   effects of these changes.
3. Global Climate Models (GCMs) predict a much
   altered climate on Earth during the next century.