Radiative forcing by changes in surface albedo caused by changes in vegetation

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Radiative forcing by changes in surface albedo
caused by changes in vegetation
Maria Malene Kvalevåg Supervisors Gunnar Myhre
and Ivar Isaksen
University of Oslo Department of Geoscience
MetOs section
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Overview

• Radiative forcing
• Previous studies
• Direct and diffuse radiation
• Methods
• MODIS
• Results
• Conclusions

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Radiative forcing

• Definition by IPCC

• Calculation at TOA

• potv potential vegetation

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IPCC 2001
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Previous studies

• Hansen et al. (1998)
• RF -0.21 W/m²
• Betts (2001)
• RF -0.20 W/m²
• Myhre and Myhre (2003)
• -0.66 W/m² lt RF lt 0.28 W/m²
• Matthews et al. (2003)
• RF -0.15 W/m²

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Direct and diffuse radiation
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Methods I

• MODerate resolution and Imaging Spectroradiometer
  (MODIS)
• Land cover product (MOD12C1)

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MODIS Land Cover Product

• 18 vegetation classes
• Globally distribution

Antropogenical vegetation classes
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Cropland and Barren
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Methods II

• MODerate resolution and Imaging Spectroradiometer
  (MODIS)
• Land cover product (MOD12C1)
• Surface albedo product (MOD43C1 v004)
• Whitesky albedo
• Blacksky albedo

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MODIS surface albedo product
Blacksky albedo
Whitesky albedo
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Methods III

• MODerate resolution and Imaging Spectroradiometer
  (MODIS)
• Land cover product (MOD12C1)
• Surface albedo product (MOD43C1 v004)
• Whitesky albedo
• Blacksky albedo
• Potential Natural Vegetation (PNV)
• Ramankutty and Foley (1999)

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Potential Natural Vegetation

• Ramankutty and Foley (1999)

• 15 vegetation classes

• No crops or
• human influenced vegetation

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Improvements

• Albedo values from Jin et al. (2002),
• ? a)
• Albedo values from Zouh et al. (2003),
• ? b)

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Blacksky values

• Albedo variation
• Seasonal
• Regional

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Global surface albedo maps
Albedo calculation
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Self-composed surface albedo data set
?albedo MODIS albedo PNV albedo pre albedo
MODIS albedo ?albedo
Constraint 0.081
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Present surface albedo from retrieved MODIS data
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Results I - Surface albedo difference
a) Jin b) Zouh c) unconstrained
MODIS d) constrained MODIS
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Results II - Radiative forcing
a) Jin, ? RF -0.091 W/m ² b) Zouh,
? RF -0.165 W/m² c) unconstrained MODIS
? RF -0.089 W/m ² d) constrained MODIS ?
RF -0.032 W/m ²
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a)
b)
c)
d)
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Conclusions

• Weaker RF results than IPCC 2001
• Same regions that contribute most to the RF
  results
• The best RF - estimate -0.032 W/m²
• Cropland value 0.15
• ?albedo has previously been to large
• Further improvements can be done by including
  MODIS snow products

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Paper submitted to Geophysical Research Letter
(GRL)

• G. Myhre, M. Kvalevåg and C. Schaaf (2005),
  Radiative forcing due to anthropogenic vegetation
  change based on MODIS surface albedo data

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Thank you ?