Aerosols: What are the links with climate & How well are we modeling them?

Chemistry-Climate Interactions

Workshop Sante Fe, 2003

Aerosols: What are the links with climate &How well are we modeling them?

W.D. Collinswww.cgd.ucar.edu/~wcollins

National Center for Atmospheric ResearchBoulder, Colorado

Acknowledgements: A. Conley, D. Fillmore, J. Kiehl, P. Rasch, NSF, and NASA



IPCC 2001 Anthropogenic Forcings



Topics

Links with Climate: Forcing

Direct radiative forcing Indirect cloud effects

• 1st: Albedo (Twomey)• 2nd: Drizzle (Albrecht)• Semi-direct: Lifetime

Feedbacks & response Temperature & lapse rate Surface fluxes Atmospheric circulation Hydrological cycle Convective diabatic

heating

Fidelity of modeling: Uncertainties in aerosols

Sources and fluxes Optical properties Magnitude of sinks Vertical transport Carbon species

Uncertainties in climate links Physics of indirect effects Magnitude of semi-direct

effects Response of shallow and

deep convection to forcing



Global Aerosol Assimilation Climatology

Analysis NCAR CAM

Aerosol Forcing

Climate Impacts

AVHRRAerosol Assimilation

Analysis

1995-2000



Satellite Aerosol Optical Depth



Carbon Emissions

(Cooke et al, 1999, and Liousse et al, 1996)



Annual Mean Aerosol Mass



Optical Depths for Each Species



Global Evaluation using Aeronet



Evaluation using Aeronet, Bermuda



Evaluation using Aeronet, Western Africa



Evaluation using Aeronet, South America



Clear-sky Radiative Forcing

TOA

Surface



All-sky Radiative Forcing

TOA

Surface



Aerosol Forcing on the Atmosphere

Clear Sky

All Sky



Shortwave Heating Rates



Change in Atmospheric Temperatures

T (2m) T (850 mb)

99% Significance99% Significance



Change in Temperature Profiles



Change in Boundary Layer Height




Change in Residual Surface Energy Flux




Change in Net Surface Longwave Flux




Change in Sensible Heat Flux




Change in Latent Heat Flux




Perturbation to Precipitation Rates

Annual

DJF




Perturbation to Near Surface Winds



Change in Atmospheric Vertical Velocity



Evaluation using MODIS Observations

(Fillmore and Collins, 2002)



MODIS Assimilation over Land and Ocean




Uncertainties in Bulk Dust Mobilization




Uncertainties in Anthropogenic Source Strengths?




Evidence from Assimilation for Speciation Errors




Uncertainties in Black Carbon from Fossil Fuels

(Bond, Rasch, Collins, and Streets, 2002)



Uncertainties in BC from Fossil Fuels (cont).

IndiaChina/SE Asia

N. Asia

N. America

Europe




Uncertainties in Primary Organic Carbon (FF)




Uncertainties in Primary OC (cont).

India China/SE Asia

N. Asia

N. America

Europe




Uncertainties in Global Carbon Aerosol Burdens

Low Central High Prev 84Emissions (Tg/year) BC Total 5.6 9.2 18.4 10.0 FF only 0.6 4.2 13.4 5.1 OC Total 31.5 34.9 44.1 38.2

FF only 0.6 4.0 13.2 7.3Burden (Tg) BC 0.18 0.26 0.47 0.28 OC 1.34 1.41 1.61 1.47Lifetime (days) BC 12 10 9 10 OC 16 15 13 14




Uncertainty in Column Burden of BC




Uncertainty in Radiative Forcing by BC




Uncertainty in Total Carbon Forcing




Sensitivity of Forcing to BC/OC Ratios

BC OCLow +0.26 -0.21Central +0.37 -0.22High +0.65 -0.25Prev 84 +0.40 -0.23

TOA Forcing Summary


(Collins et al, 2002)



Observed vs Modeled Radiative Sensitivity

(Collins et al, 2002)(Satheesh and Ramanathan, 2002)



Optical Effects of Internal vs. External Mixing

(Ramanathan et al, 2001)

Pure external → internal mixture 10% variations in forcing, AOD



Sensitivity to Scavenging Parameterizations

(Mahowald and Rasch, 2002)



Vertical Distribution of Aerosols





Global Information on Vertical Aerosol Profiles

Based upon MATCH, unobserved mass =

• 86% of carbonaceous species

• 97% of soil dust

• 85% of sulfate

• >99% of sea salt

(http://www-sage2.larc.nasa.gov)



All-Sky Aerosol Radiative Forcing

(Collins et al, 2002)




Global All-Sky Aerosol Forcing



Issues

• TOA forcing due to carbonaceous species– Partial cancellation between OC and BC– Sign of forcing dependent on inventory.

• Radiative effects of absorbing aerosols – Vertical relationship to clouds is highly uncertain.– Vertical profile is dependent on shallow/deep convective

parameterizations.

• Effects of aerosols on climate system– Answers may(will) differ on coupling to ocean/land

surfaces.– Quantification requires uncoupled and coupled

experiments.

• Better quantification requires better inventories.

Aerosols: What are the links with climate & How well are we modeling them?

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