1. Chemistry, Aerosols, and Climate: Tropospheric Unified Simulation (CACTUS)
Objective: to improve understanding of interactions between atmospheric chemistry, aerosols, and climate

2. Approach: coupled chemistry-aerosol-climate GCM
CACTUS model
Atmospheric
chemistry
Emissions
land use
climate forcing
GISS GCM
Aerosol
microphysics
D climate
chemistry

3. Combined radiative forcings from tropospheric ozone and sulfate, 1800-2000

4. CACTUS contributions to IPCC 2001 report

5. 1800-2000 radiative forcing from tropospheric ozone is less well constrained than implied by IPCC
Standard preindustrial simulation:
DF = 0.44 W m-2
“Adjusted” preindustrial simulation
(lightning and soil NOx decreased,
biogenic hydrocarbons increased):
DF = 0.80 W m-2

6. CACTUS contributions to IPCC 2001 report

7. Aerosol microphysics in CACTUS model
North America
202 cm-3
6.3 mg/m3
Number Concentration
South Pacific
74 cm-3
0.13 mg/m3
0.01
0.1 1 10
Dry Diameter (mm)

8. Next CACTUS phase: aerosol-chemistry-climate coupling for 2000-2100
Step 1b: GCM simulation
long-lived GG
Current O3, OH, aerosols
Step 1a: CACTUS simulation
D Emissions
Current climate
Diagnose D climate from
aerosol-chemistry-climate
interactions
Diagnose D chemistry
due to climate change
Step 2: CACTUS simulation
D Emissions
D climate increments: 2025, 2050, 2075, 2100
Step 3: GCM simulation
long-lived GG
D O3, OH, aerosols
iterate
Step 4: fully coupled simulation

9. SF6 simulation in 2xCO2 climate: comparison to present climate
Stronger convective transport
Weaker interhemispheric exchange

10. SF6 simulation in 2xCO2 climate: comparison to present climate (cont.)
stronger stratospheric circulation and stratosphere-troposphere exchange