ipcc chapter 7 - university of washington
TRANSCRIPT
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IPCC Chapter 7
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IPCC Chapter 7 discussion
7.2: Clouds7.3: Aerosols7.4: Aerosol-cloud interactions7.5 Radiative forcing by anthropogenic aerosols
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Changes in the way aerosol effective forcing components are assessed
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Terminology
• aci (aerosol-cloud interactions)
• ari (aerosol-radiation interactions)
• RFari (Radiative forcing associated with ari)direct effect
• ERFari (Effective radiative forcing associated with aridirect + semidirect
• RFaci (Radiative forcing associated with aci)albedo effect
• ERFaci (effective radiative forcing associated with acialbedo + lifetime effects
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7.2 Clouds
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Parameterization of Clouds in Climate Models
• Challenges– Microphysical processes remain poorly understood, esp. in the
ice and mixed phase
– Subgridscale cloud variability important (models typically use 100-200 km horizontal and 100-1000 m vertical resolution)
– Different aspects of cloud behavior controlled by different parameterizations (e.g., turbulent mixing scheme; shallow+deep convection; large-scale cloud; radiation)
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Parameterization of Clouds in Climate Models
• Recent advances in cloud microphysical processes– Since AR4, most models now have fully interactive aerosol schemes
– Improved representation of subgridscale variability
– Droplet activation schemes often use vertical winds consistent with their turbulent mixing schemes
– More complete representation of ice and mixed phase clouds
• Allow ice supersaturation
• Explicit treatment of Bergeron-Findeisen process [still not in most models, but in some]
– Improved representation of turbulent mixing and convection
• Better coupling between turbulence and convection schemes
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7.3 Aerosols
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Anthropogenic (+biomass burning)
• Africa accounts for 50% of global BB aerosols
• Unclear whether BB aerosols are anth or natural
• SOA has huge uncertainty range, not captured here
• Asia accounts for 50% of anthropogenic BC
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• Natural sulfur emissions more uncertain than, but comparable with, anthropogenic ones
• SOA production from biological VOCs highly uncertain and may rival anth. Sources
• How much natural BC?
Natural
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Fig 7.14
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Black carbon
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Even knowing emissions isn’t enough
• Particle size matters
• Aerosol mixing state important
• Aerosol processing (oxidation etc.)
• Aerosol sinks are poorly understood
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Some BOE
• Total AOD = 0.12
• Of which AEROCOM assesses anthropogenic component of AOD = 0.03 ( 30 = 0.9 W m-2 clear sky Rfari, with 2/3 masked by clouds
• all sky Rfari 0.3 W m-2 (similar to assessed value)
• Between ¼ and 2/3 of CCN globally are assessed to be anthropogenic with low confidence
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Aerosol responses to climate change(elephants in the room?)
• More dust (land use changes, soil moisture)?
• More or less sea-salt? (water viscosity and whitecap fraction depends on SST, wind speed changes)
• More SOA precursors (poss. 50% increase in isoprene by 2100?)
• More DMS?