MET 112 Global Climate Change Lecture 13

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MET 112 Global Climate Change - Lecture 13

• Radiative Forcing
• Eugene Cordero
• San Jose State University

• Outline
• GHG/Aerosols
• Radiative Forcing
• Activity

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Current CO2 370 ppm
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Radiative Forcing

• A change imposed upon the climate system which
  modifies the Earths energy (radiative) balance.
• This change
• Radiative forcing is usually given in units of
• Positive values of radiative forcing
• Negative values of radiative forcing

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Radiative Forcing

• A change imposed upon the climate system which
  modifies the Earths energy (radiative) balance.
• This change
• increases or decrease the Earths energy balance.
• Radiative forcing is usually given in units of
• watts per square meter (W/m2),
• Positive values of radiative forcing
• contribute to heating of the surface,
• Negative values of radiative forcing
• Contribute to cooling of the surface.

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Radiative Forcing

• Examples of radiative forcing mechanisms include
• Changes in atmospheric composition

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Radiative Forcing

• Examples of radiative forcing mechanisms include
• Changes in solar intensity
• Volcanic activity
• Changes in atmospheric composition
• CO2
• Aerosols
• Ozone

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Radiative Forcing

• Changes in these mechanisms
• The magnitude of the radiative forcing determine
  how strong the effect is.
• Radiative forcing is computed by comparing

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Radiative Forcing

• Changes in these mechanisms
• produces changes to the earth energy budget.
• The magnitude of the radiative forcing determine
  how strong the effect is.
• Radiative forcing is computed by comparing
• Pre-industrial (1750) with today (2000)

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Anthropogenic Forcing

• Without doubt, humans have altered the radiative
  balance of the Earth system. The changes can be
  partitioned into the following categories
• Enhanced greenhouse gases
• CO2, CH4, N2O, CFCs
• Ozone
• Aerosols (Natural and Anthropogenic)
• Sulfate
• Carbon
• Land Use Changes

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Anthropogenic Forcing

• Without doubt, humans have altered the radiative
  balance of the Earth system. The changes can be
  partitioned into the following categories
• Enhanced greenhouse gases
• CO2, CH4, N2O, CFCs
• Ozone
• Tropospheric
• Stratospheric
• Aerosols (Natural and Anthropogenic)
• Sulfate
• Carbon
• Biomass burning (black carbon)
• Land Use Changes

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Enhanced Greenhouse Gases

• Greenhouse gas concentrations have increased over
  the last 150 years dramatically
• The main anthropogenic contribution to greenhouse
  gases concentrations include
• CO2, CH4, N2O, CFCs (Halons)
• Increases in greenhouse gas concentrations are
  well observed

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Enhanced Greenhouse Gases

• Greenhouse gas concentrations have increased over
  the last 150 years dramatically
• The main anthropogenic contribution to greenhouse
  gases concentrations include
• CO2, CH4, N2O, CFCs (Halons)
• Increases in greenhouse gas concentrations are
  well observed
• Radiative Forcing positive

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Ozone

• Ozone exists in upper atmosphere
• Ozone layer (stratospheric ozone)
• Ozone layer protects the earth from harmful UV
  radiation
• Stratospheric ozone levels have been declining
  over last 20 years (ozone depletion)
• Ozone exists in lower atmosphere
• Tropospheric ozone levels have increased over
  last 20 years.

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Ozone

• Ozone exists in upper atmosphere
• Ozone layer (stratospheric ozone)
• Ozone layer protects the earth from harmful UV
  radiation
• Ozone layer responsible for heating the
  stratosphere
• Stratospheric ozone levels have been declining
  over last 20 years (ozone depletion)
• Radiative Forcing negative
• Ozone exists in lower atmosphere
• Smog (tropospheric ozone)
• Tropospheric ozone levels have increased over
  last 50 years.
• Radiative Forcing positive

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Land Use Change

• Changes in the land use have contributed to
• Deforestation has been largest contributor
• High latitudes have been most affected
• Pre Industrial Snow covered forests (low
  albedo)
• Again, large uncertainties remain

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Land Use Change

• Changes in the land use have contributed to
• Albedo changes
• Deforestation has been largest contributor
• High latitudes have been most affected
• Pre Industrial Snow covered forests (low
  albedo)
• Current Open snow covered areas (high albedo)
• Again, large uncertainties remain
• Radiative Forcing negative

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Radiative Forcing
Positive Values Negative Values
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Radiative Forcing
Positive Values Warming the Earths
surface Negative Values Cooling the Earths
Surface
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Radiative Forcing from the IPCC
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Radiative Forcing from the IPCC
What does this plot mean?
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Radiative Forcing from the IPCC
What does this plot mean? Increases in greenhouse
gases (CO2, CH4, N2O and Halocarbons) between
1750 through today (2000) have caused a 2.4 Watts
per meter squared increase in the earths
radiation budget. This by itself would warm the
earths surface.
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Radiative Forcing from the IPCC
What does this plot mean? Increases in greenhouse
gases (CO2, CH4, N2O and Halocarbons) between
1750 through today (2000) have caused a 2.4 Watts
per meter squared increase in the earths
radiation budget. This by itself would warm the
earths surface. Radiative forcing 2.4 ? 0.2
or between 2.2 and 2.6
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Radiative Forcing example

• Imagine that the only two anthropogenic forcing
  terms changing the climate are
• Greenhouse Gases
• Ozone Depletion
• Calculate the radiative forcing just due to those
  two terms including the uncertainties

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Radiative Forcing example

• Imagine that the only two radiative forcing terms
  are changing the climate are
• Greenhouse Gases
• Ozone Depletion
• Calculate the radiative forcing just due to those
  two terms including the uncertainties

2.4 ? 0.2 (2.2 to 2.6)
-0.1 ? 0.1 (0 to -0.2)
Mean 2.3 Range of values between (2.0 to
2.6) Positive Forcing!
Add the two forcing terms 2.4 (-0.1)
2.3 Calculate range of values (Mean) 2.6 0
2.6 2.2(-0.2)2.0
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Uncertainty or Range of values possible

• To calculate the range of possible values
• Add the most positive radiative forcing
• Add the most negative radiative forcing
• This will determine the range of possible values.

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Activity 8 (Due Tuesday Nov 2nd)

• Calculate the total mean radiative forcing from
  the provided figure of individual radiative
  forcing from the IPCC. You may omit the mineral
  dust and aviation terms. Please show your work!
• Calculate the total range of possible values from
  the above calculation
• What conclusions does the total mean radiative
  forcing tell us about how the climate has
  changed?
• How does the range of values (or uncertainties)
  affect our above conclusions?

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Uncertainties

• Although you can examine the radiative forcing,
  you must also consider the uncertainties of each
  estimate!
• The uncertainties in our understanding of the
  climate system make definite predictions more
  challenging.
• However, estimates of uncertainties also provide
  valuable information!

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Radiative Forcing from the IPCC
Term Mean Low High CO2 etc. 2.4 2.2 2.6 Stra
t o3 -0.1 -0.2 0 Trop O3 0.4 0.3 0.5 Sulfate
-0.4 -0.6 -0.3 Black Carbon 0.2 0.1 0.4 Orga
nic Carbon -0.1 -0.2 0 Biomass
burn -0.2 -0.6 -0.1 Tropo indirect 0 -2.0 0 So
lar -0.2 -0.4 0 Total 2.2 -1.4 3.1