Federal Science Research on the Role of Aerosols in Climate Change

Sylvia A. Edgerton*

National Science Foundation

Workshop on Secondary Organic Aerosols, Reno NV February 5, 2002

* Thanks to Dr. Joel Levy, Atmospheric Chemistry Program Manager at NOAA, for preparing many of the slides related to aerosols and climate.

Aerosols and Climate

• Aerosols are intimately and significantly linked to the workings of the climate system– Historical view understates the role of aerosols in climate– Aerosols exert very large regional effects not reflected in global averages– Aerosols significantly influence surface energy flux budgets– Aerosols may significantly influence precipitation

• Focused aerosol/climate research is an essential for operational climate prediction – Critically selected measurements are required– Research must be targeted at conceptual breakthroughs

Aerosol Radiative Forcing Mechanisms

• Direct Effect

– Light Scattering and Absorption==> surface cooling, atmospheric warming

• 1st Indirect Effect (Twomey Effect) – Decreased cloud droplet size

– Increased cloud droplet concentrations==> brighter clouds

• 2nd Indirect Effect (feedback?)

– Increased cloud lifetime and/or thickness ==> suppression of drizzle

• Semi-Direct Effect (feedback?)

– Cloud burning due to atmospheric heating

IPCC(2001) Global and Annual Mean Radiative Forcing

What’s not in this picture?

• Aerosol 2nd indirect effect omitted

• Aerosol semi-direct effect omitted

• Regional character of aerosol forcing not represented

• Aerosol models are largely unvalidated

Aerosol Indirect RadiativeForcing

Indirect aerosol forcing is the singlelargest source of uncertainty in theradiative forcing of the climatesystem.

IPCC 2001

What are aerosol indirect effects?

Aerosol-forced perturbations in cloud optical properties, resulting from changes

in cloud drop concentration, physical thickness, effective radius, and horizontal

extent (cloud fraction) that lead to a change in the earth's cloud radiative

forcing

IPCC (1995) - Invoked aerosol cooling to offset GCM overestimates of greenhouse warming

Crude Aerosol Model

• Sulfate only

• Light-scattering only phenomenon included

• Impact on albedo computed off-line

Radiative Forcing by Species

Hansen (2001)

Optical Properties of Aerosols

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Contribution of Chemical Components to Submicron Extinction for ACE 1 and INDOEX Air Masses

(550 nm and 55% RH)

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Contribution of Chemical Components to Aerosol Optical Depth for TARFOX

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Data courtesy of QuinnHegg et al (1997)

Results from recent field

programs suggest that

regional aerosol-induced

surface cooling is large!

Large-scale observational evidence for suppression of precipitation by aerosols

Aerosol 2nd Indirect Effect==> Small droplets coalesce less

efficiently than large droplets

• AVHRR image over Australia shows pollution tracks from

– power plant (5), smelter (6), port (7), refinery (8)

• Yellow denotes smaller cloud droplets• Co-located measurements from

TRMM/PR show – precipitation outside pollution tracks– no precipitation inside pollution tracks

• Similar observations have been made for biomass smoke and dust

D. Rosenfeld, Science 287, 1793 (2000)

Recommendations for future research from a recent workshop on aerosol-climate interactions

Scripps Institution of Oceanography January 2002

• Characterize the sources, distribution, and properties of aerosols and their influence on cloud formation and rainfall, globally and a region-by-region basis

• Represent aerosol impacts in climate models by linking their representation to these observations

• Quantify the relative importance of aerosols and greenhouse gases for global warming

Science Management in the Federal Government

Office of Science and Technology Policy

Office of Management and Budget

National Science and Technology Council Committee on Environment and Natural

Resources (CENR)

Research Subcommittees

Air Quality

Ecological Systems

Global Change

Natural Disaster Reduction

Toxics and Risk

Member Agencies

Department of Agriculture Department of CommerceDepartment of DefenseDepartment of EnergyDepartment of Health and Human Services Department of Housing and Urban DevelopmentDepartment of StateDepartment of the InteriorDepartment of Transportation Environmental Protection AgencyNational Aeronautics and Space AdministrationNational Science FoundationOffice of Management and BudgetOffice of Science and Technology PolicyTennessee Valley Authority

Atmospheric Composition Program Element

Focuses on improving our understanding of the global- and regional-scale impacts of natural and human processes on the composition of the atmosphere; and determining the effects of such changes on air quality and human health.

FY 2002USGCRP Annual Budget Request to Congress

OUR CHANGING PLANETTHE FY 2002

U.S. GLOBAL CHANGE RESEARCH PROGRAM

A Report by the Subcommittee on Global Change Research,Committee on Environment and Natural Resourcesof the National Science and Technology Council

Interagency Air Quality Research Subcommittee

PM Strategy Goal:

Enhance the scientific information base for public policy that protects the public health (of primary importance) and the environment from harmful effects due to airborne particulate matter.

Targeted to provide a current description of PM formation and transport with an evaluation of the science tools to support implementation.

NARSTO PM Assessment

NARSTO PM Assessment

Support the 2003 review of the PM Canada Wide Standards and the implementation of that standard.

Assist with the development of State Implementation Plans in the U.S. starting in 2003.

Support the joint international work leading up to negotiation of a PM Annex under the Canada/US Air Quality Accord.

In Mexico it will support their PROAIRE program to improve air quality in Mexico City.

Characterize the chemical composition of the atmosphere and its variability

Understand the processes by which chemicals are transformed and transported in the atmosphere

Quantify the major fluxes of a wide variety of important substances into and out of the atmosphere, and to understand the processes controlling those fluxes

Understand the natural and anthropogenic causes of atmospheric chemical variability, and the effects of chemical change on climate.

NSF Atmospheric Chemistry Program

Primary Goals:

Understand the role of atmospheric chemistry in the radiation budget of the Earth, i.e. greenhouse gases, stratospheric ozone, aerosols, cloud radiative forcing;

Provide information about the processes leading to the emissions and atmospheric deposition of biologically important chemicals, i.e. acid deposition, nutrient cycling, biomass burning and its relationship to land use practices, carbon cycle, etc.;

Understand how natural and anthropogenic emissions interact with the atmospheric chemical system to affect regional air quality.

NSF Atmospheric Chemistry Program

Crosscutting Goals:

FY01 ATC ProgramProject Type

10%

51%

25%

11% 3%

Instrumentation DevelopmentField measurementsLaboratory studiesNumerical modelingOther

FY01 ATC ProgramProject Focus

45%

7%

41%

4% 3%

Atmospheric Aerosols

Biogeochemical Cycles

Regional Chemistry/Air Quality

Stratospheric Chemistry

Other