1. The other Harvard 3-D model: CACTUS Chemistry, Aerosols, Climate: Tropospheric Unified Simulation Objective: to improve understanding of the interaction between chemistry, aerosols, and climate GISS Harvard CalTech UC Irvine Carnegie Mellon (Goddard)

2. Anatomy of a Unified Model GISS GCM II’ calculates meteorology GHG concentrations, solar flux, land surface characteristics CalTech aerosol module Harvard chemistry module aerosol tropospheric ozone temperature, humidity, wet dep, clouds, winds, etc precursor emissions aerosol, gases

3. What follows: Alternative, practical approaches, with tie-in to GEOS CHEM Fully coupling a model is ambitious and CPU-intensive! (wallclock time: 10 days/model year) Equilibrium climate simulations: 75-100 years, including spin-up Transient simulations: 50 years just for ocean spin-up

4. Chapter 1: Calculate radiative forcing due to increase in tropospheric ozone (Mickley et al., 1999, 2001) GISS GCM II’ GHG concentrations, solar flux, land surface characteristics Harvard chemistry module meteorology Specified aerosol. Present-day & preindustrial precursor emissions (run twice) ozone Forcing calculation Calculated ozone does not influence climate

5. Uncertainty of radiative forcing due to O 3 is quite large. Standard simulation,  F = 0.44 Wm -2 Test simulation with natural emissions within range of uncertainty  F = 0.80 Wm -2 (about 1/2  F of CO 2 ) obs, late 1800s test model std model Mickley et al., 2001 Preindustrial ozone monthly means

6. Chapter 1 continued: Do same forcing calculation for sulfate aerosol (Adams et al., 1999) GISS GCM II’ GHG concentrations, solar flux, land surface characteristics CalTech aerosol module aerosol meteorology precursor emissions nitric acid Forcing calculation Harvard offline chemistry

7. Nitrate forcing may have large impact over 21 st century  F preindustrial to present-day for sulfate+nitrate = -1.14 Wm-2  F preindustrial to 2100 for sulfate+nitrate = -2.13 Wm-2 2100 annual averaged forcing due to sulfate+nitrate aerosol Adams et al., 2001

8. Chapter 2: Begin to unify model (Liao et al., 2003) GISS GCM II’ GHG concentrations, solar flux, land surface characteristics CalTech aerosol module Harvard chemistry module aerosol ozone meteorology precursor emissions oxidants, nitric acid Forcing calculation

9. Heterogeneous chemistry decreases ozone at the surface Ratio of annual mean mixing ratios of ozone: With het chem / without hem chem Includes ozone uptake on mineral dust. Liao et al., 2003

10. Chapter 3: Calculate equilibrium climate response to changing tropospheric ozone (Mickley et al., 2003) GISS GCM II’ calculates meteorology GHG concentrations, solar flux, land surface characteristics Harvard chemistry module archived monthly mean ozone fields precursor emissions Calculate preindustrial and present-day ozone fields beforehand, using present-day climate.

11. Results from GCM equilibrium simulation with present-day vs. preindustrial tropospheric ozone  T = 0.3 o C  F = 0.49 W m -2 Preindustrial ozone equilibrium climate Present-day ozone Mickley et al., 2003

12. Inhomogeneity of climate response to tropospheric ozone change over 20 th century Greater warming in northern hemisphere (due to more ozone and albedo feedback in Arctic) Strong cooling in stratosphere (>1 o C in Arctic winter): Surface Tropospheric ozone 9.6  m Stratospheric ozone Global SH NH

13. Chapter 3 continued (Chung et al., in progress) Do same with Caltech aerosol: Feed monthly mean preindustrial and present-day aerosol fields into GISS GCM.

14. Chapter 4: Build interface between GISS GCM and GEOS CHEM to study past and future climates GISS GCM II’ GHG concentrations, solar flux, land surface characteristics GEOS CHEM calculates chemistry, aerosol precursor emissions archived temperatures, humidity, winds, etc First application: investigate effect of future climate change on US air quality (Mickley, Shiliang Wu)

15. Chapter 4 continued: Diagnose effect of changing climate on US air quality (transient simulation) 1950 2000 2025 2050 2075 2100 GISS GCM, with changing GHGs Spin-up of ocean GEOS-CHEM Calculate chemistry, aerosol present-day precursor emissions archived temperatures, humidity, winds, etc

16. Chapter 5: Investigate effect of aerosol and tropospheric ozone on future climate precursor emissions 1950 2000 2025 2050 2075 2100 GISS GCM, with changing GHGs + ozone, aerosol Spin-up of ocean GEOS-CHEM Calculate chemistry, aerosol archived temperatures, humidity, winds, etc 1950 2000 2025 2050 2075 2100 Develop 100-year forecast of ozone, aerosol

17. Chapter 6: Investigate indirect effect of aerosols (Adams, DelGenio) Acknowledgments: Brendan Field, David Rind, Jean Lerner, Reto Ruedy, Gavin Schmidt, Drew Shindell, Andy Lacis, Prashant Murti, Bob Yantosca