Federal Science Research on the Role of Aerosols in Climate Change

1. 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.

2. 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

3. 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

4. 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

6. 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

7. 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

8. Radiative Forcing by Species Hansen (2001)

9. Optical Properties of Aerosols Data courtesy of Quinn Hegg et al (1997)

10. Results from recent field programs suggest that regional aerosol-induced surface cooling is large!

11. 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)

12. Recommendations for future research from a recent workshop on aerosol-climate interactionsScripps 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

13. Science Management in the Federal Government Office of Science and Technology Policy Office of Management and Budget

14. 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

15. Member Agencies Department of Agriculture Department of Commerce Department of Defense Department of Energy Department of Health and Human Services Department of Housing and Urban Development Department of State Department of the Interior Department of Transportation Environmental Protection Agency National Aeronautics and Space Administration National Science Foundation Office of Management and Budget Office of Science and Technology Policy Tennessee Valley Authority

16. 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.

17. OUR CHANGING PLANET THE FY 2002 U.S. GLOBAL CHANGE RESEARCH PROGRAM FY 2002 USGCRP Annual Budget Request to Congress A Report by the Subcommittee on Global Change Research, Committee on Environment and Natural Resources of the National Science and Technology Council

18. 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.

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

20. 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.

21. NSF Atmospheric Chemistry Program Primary Goals: • 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.

22. NSF Atmospheric Chemistry Program Crosscutting 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.