IPCC (2007) and the NAS/NRC Committee on Radiative Forcing Effects on Climate

1. IPCC (2007) and the NAS/NRC Committee on Radiative Forcing Effects on Climate Susan Solomon, co-chair, IPCC WGI and senior scientist, NOAA Aeronomy Laboratory

2. An NRC report that was an important input to the TAR IPCC (2007): Solomon (USA) and Qin (China), co-chairs Climate Change 2007 The Physical Science Basis This committee: an important opportunity for similar synergy through dialogue IPCC (2001): Houghton (UK) and Ding (China), co-chairs

3. We are here: the outline is in final form and is about to be submitted to the Plenary for approval Apr 2003 First scoping meeting Sep 2003 Second scoping meeting Nov 2003 Panel approval of outlines for reports Apr 2004 Lead author teams selected by WGI Bureau Sep 2004 Lead Author meeting 1 (Trieste) Feb 2005 Zero order draft complete May 2005 Lead Author meeting 2 (Beijing) This committee’s report is due just before WGI authors begin first formal draft Aug 2005 First draft complete Dec 2005 Lead Author meeting 3 (Christchurch) Feb 2006 Second draft complete Jun 2006 Lead Author meeting 4 (TBD) Jan 2007 WGI panel Time Line Issues

4. What does UNFCCC want? • Strong scientific messages telling an integrated story – not a grab bag of topics • Clear expository graphics, avoiding “mathematical magic” • Clear explanation of uncertainties and limits to understanding • Address key questions • Skip unnecessary repetition of earlier reports (very important) - this forced tough choices • Shorter and “more focussed”

5. Radiative Forcing: A key topic, as in past reports…assess anthropogenic and natural influences on radiative balance • Review/update past and estimated future radiative forcing for greenhouse gases, and.. • ..for aerosols including indirect effects (sulfate, nitrate, organic, soot….) • Land use/surface albedo effect • Aviation (e.g., new studies on cloud interactions) • Compare with natural forcings (solar, volcanic). • Roles of short-lived vs long-lived species • Forcing/response relations in the global mean - use and limits of the radiative forcing concept; • GWP and other metrics for comparing emissions

6. More information on dependence of climate change on forcing mechanism LS O3 CO2 Solar UT O3 An updated and improved assessment of:•Solar•Aviation•Land use•Aerosols!• esp. soot!• Gases!•GWPs and other metrics Joshi et al (2003)

7. How to best convey our message? Many key warming agents live for decades or more All known cooling agents are short-lived AR4: stronger emphasis on timescales

8. Paleoclimate: More links to forcing • Use paleoclimatic information to provide greater clarity on what may be natural versus manmade (globally and regionally) • Illuminate key vulnerabilities to changes in radiative forcing • Paleoclimate as a basis for testing cause and effect relationships (e.g., volcanoes and solar) • What happened in the past and why – focus on observations and processes • Discuss paleo measurements in greater depth - tree rings, ice cores, etc. • More careful analysis of how anomalous the last century has been • Review/ update what is known of abrupt climate changes – the potential wild card

9. Compare to models (including volcanoes, solar, and anthropogenic forcing) for more than 1000 years 7 NH records Model with volcanoes, solar, and GHG/aerosol Tambora From Crowley, personal communication

10. Couplings between changes in the climate system and biogeochemistry: “Beyond radiative forcing” • Describe the emerging linkages in understanding and simulating the fully coupled system • Carbon cycle / climate interactions – increasing respiration vs photosynthesis, coupling of C and N biogeochemistry, aerosol/diffuse flux linkages…. • Global atmospheric chemistry and climate change - processes influencing global ozone and methane in a coupled system, coupling of stratosphere to surface change, …. • Air quality and climate change - interactions on new scales, where increasing numbers of people live • Aerosols – aerosol/hydrological cycle feedbacks; regional and global scale analyses of coupled aerosol/ chemistry / climate interactions, …. • Land surface / hydrology including e.g., fires, dynamic vegetation models • Should better identify possible ‘wild cards’ that could emerge in an altered climate state

11. One example of a coupled interaction: Sea-salt emissions = function (wind speed) Transport (advective, convective) and deposition =function(climate) ==> “in my opinion an assessment is needed in AR4” - O. Boucher, Marrakech, 2003 A need to go “beyond radiative forcing” to the fully coupled system of human/climate interactions.

12. Interesting new papers on aerosol forcings and responses at various levels: A key assessment challenge for WG I Aerosols potentially influence precipitation at microphysical level (precipitation efficiency); sub-grid scale (altered convection); and large scale (altered circulation patterns). Menon et al.: black carbon (soot) and Asian precipitation. How well understood are the forcings? Surface fluxes/TOA? Rostayn and Lohmann: suggesting a link of aerosols to the drought in Africa. See also work by Rosenfeld and others on other aerosol processes that could play a role.

13. Some areas of focus that this committee may wish to consider: • Definitional issues: How should we think about surface / tropopause / TOA forcings? What is a forcing and what is a feedback? • Aerosols: direct and indirect effects; aerosol linkages to land use effects (e.g., biomass burning, wind stress, etc.) • Air quality/climate: a two-way story • Solar and volcanic forcings: satellite era and before, including paleo. What is a forcing and what is a feedback, across a range of time scales?

14. Top-of-the-atmosphere Surface (Wm-2) March 97 Definitions: Radiative processes and their spatial distributions Implications for radiative forcing? And the more general question: what is a forcing and what is a feedback?

15. Aerosols: A Major Issue • Particle number, size, precipitation efficiency, liquid water content are all factors in climate • Do continental clouds have different feedbacks to aerosols than marine clouds? • New research on black carbon (soot) and on gradients in radiative forcing (sulfate) • Coupling of land use/vegetation/fires/aerosols issues

16. Air Quality/Climate: More people are living the experience UN, World Urbanization Prospects The 2002 Revision

17. Mexico City from Satellites GOME NO2 December average Data courtesy J. Burrows, U. Bremen Processing by S. Massie, NCAR

18. AR4 TAR SAR FAR Solar Forcing: Three full solar cycles of direct observations of the solar irradiance. What are the constraints on solar/volcanic effects over the past three cycles, compared to human activities?

19. Past climates: what do they tell us about radiative forcing and responses, as well as feedbacks? Last Ice age Last interglacial

20. Concluding remarks • There are many opportunities for synergy; this presentation is a ‘sampler’. • Timing IPCC/NRC is complementary • Thanks for this initial discussion