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MET 112 Global Climate Change Lecture 13

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Pre Industrial: Snow covered forests (low albedo) Again, large uncertainties remain ... understanding of the climate system make definite predictions more challenging. ... – PowerPoint PPT presentation

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Title: MET 112 Global Climate Change Lecture 13


1
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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  • Important As you are viewing this lecture, make
    sure you can see the notes section of the
    screen. There is a button on the bottom which
    says notes which you can click or manually resize
    the screen to enable the notes to be seen.

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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

8
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.

9
Radiative Forcing
  • Examples of radiative forcing mechanisms include
  • Changes in atmospheric composition

10
Radiative Forcing
  • Examples of radiative forcing mechanisms include
  • Changes in solar intensity
  • Volcanic activity
  • Changes in atmospheric composition
  • CO2
  • Aerosols
  • Ozone

11
Radiative Forcing
  • Changes in these mechanisms
  • The magnitude of the radiative forcing determine
    how strong the effect is.
  • Radiative forcing is computed by comparing

12
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)

13
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

14
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

15
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

16
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

17
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.

18
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

21
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

22
Radiative Forcing
Positive Values Negative Values
23
Radiative Forcing
Positive Values Warming the Earths
surface Negative Values Cooling the Earths
Surface
24
Radiative Forcing from the IPCC
25
Radiative Forcing from the IPCC
What does this plot mean?
26
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.
27
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
28
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

29
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
30
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.

31
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?

32
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!

33
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
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