The other Harvard 3-D model: CACTUS
Chemistry, Aerosols, Climate: Tropospheric Unified
Simulation
GISS
Harvard
CalTech
UC Irvine
Carnegie Mellon
(Goddard)
Objective: to improve understanding of the interaction between
chemistry, aerosols, and climate
Anatomy of a Unified Model
GHG concentrations,
solar flux, land surface
characteristics
GISS GCM II’
calculates
meteorology
aerosol
CalTech
aerosol
module
tropospheric ozone
temperature,
humidity, wet
dep, clouds,
winds, etc
aerosol, gases
precursor emissions
Harvard
chemistry
module
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
What follows: Alternative, practical approaches,
with tie-in to GEOS CHEM
Chapter 1: Calculate radiative forcing due to increase in
tropospheric ozone (Mickley et al., 1999, 2001)
GHG concentrations,
solar flux, land surface
characteristics
GISS GCM II’
Forcing
calculation
ozone
Calculated ozone does
not influence climate
meteorology
Specified aerosol.
Present-day &
preindustrial precursor
emissions (run twice)
Harvard
chemistry
module
Uncertainty of radiative forcing due to O3 is quite large.
std model
test model
obs, late 1800s
Standard simulation,
DF = 0.44 Wm-2
Test simulation with
natural emissions within
range of uncertainty
DF = 0.80 Wm-2
(about 1/2 DF of CO2)
Preindustrial ozone monthly means
Mickley et al., 2001
Chapter 1 continued: Do same forcing calculation for sulfate
aerosol (Adams et al., 1999)
GHG concentrations,
solar flux, land surface
characteristics
Forcing
calculation
GISS GCM II’
aerosol
meteorology
CalTech
aerosol
module
nitric acid
precursor emissions
Harvard offline
chemistry
Nitrate forcing may have large impact over 21st century
DF preindustrial to
present-day for
sulfate+nitrate =
-1.14 Wm-2
DF preindustrial to
2100 for
sulfate+nitrate =
-2.13 Wm-2
2100 annual averaged forcing due to sulfate+nitrate aerosol
Adams et
al., 2001
Chapter 2: Begin to unify model (Liao et al., 2003)
GHG concentrations,
solar flux, land surface
characteristics
Forcing
calculation
GISS GCM II’
aerosol
Forcing
calculation
ozone
meteorology
CalTech
aerosol
module
oxidants, nitric acid
precursor emissions
Harvard
chemistry
module
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
Chapter 3: Calculate equilibrium climate response to changing
tropospheric ozone (Mickley et al., 2003)
GHG concentrations,
solar flux, land surface
characteristics
GISS GCM II’
calculates
meteorology
Calculate preindustrial and
present-day ozone fields
beforehand, using present-day
climate.
precursor emissions
archived monthly
mean ozone fields
Harvard
chemistry
module
Results from GCM equilibrium simulation with present-day vs.
preindustrial tropospheric ozone
equilibrium
climate
Present-day ozone
Preindustrial ozone
DF = 0.49 W m-2
DT = 0.3oC
Mickley et al., 2003
Inhomogeneity of climate response
to tropospheric ozone change over 20th century
Greater warming in northern
hemisphere (due to more ozone
and albedo feedback in Arctic)
Global
NH
Strong cooling in stratosphere
(>1oC in Arctic winter):
Stratospheric
ozone
SH
Tropospheric
ozone
9.6 mm
Surface
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.
Chapter 4: Build interface between GISS GCM and GEOS CHEM to
study past and future climates
GHG concentrations,
solar flux, land surface
characteristics
GISS GCM II’
First application: investigate
effect of future climate
change on US air quality
(Mickley, Shiliang Wu)
archived
temperatures,
humidity,
winds, etc
GEOS CHEM
calculates
chemistry, aerosol
precursor emissions
Chapter 4 continued: Diagnose effect of changing climate on US
air quality (transient simulation)
GISS GCM, with changing GHGs
1950
2000
Spin-up of ocean
2025
2050
2075
2100
archived
temperatures,
humidity, winds, etc
GEOS-CHEM
Calculate chemistry, aerosol
present-day precursor emissions
Chapter 5: Investigate effect of aerosol and tropospheric ozone on
future climate
GISS GCM, with changing GHGs + ozone, aerosol
1950
2000
Spin-up of ocean
2025
2050
2075
2100
archived
temperatures,
humidity, winds, etc
GEOS-CHEM
Calculate chemistry, aerosol
precursor emissions
Develop 100-year forecast of ozone, aerosol
1950
2000
2025
2050
2075
2100
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