Climate Change 2001:
Working Group I: The Scientific Basis
Other reports in this collection

5.4.3 Modelling the Indirect Effect of Aerosols on Global Climate Forcing

Published estimates of the indirect forcing by anthropogenic aerosols are summarised in Table 5.11. The results in Table 5.11a are for the assumption that changes in initial droplet concentrations do not lead to any changes in cloud properties. These results, therefore, did not include any feedbacks to liquid-water content or cloud amount as a result of changes to precipitation efficiency. The results in Table 5.11b include a calculation of the decrease in precipitation efficiency that results from an increase in Nd. Therefore, these results do include feedbacks to changes in liquid-water and cloud amount from changes in cloud microphysics.

Table 5.11a: Comparison of model-predicted indirect forcing without cloud amount and liquid-water path feedback.
Model
Pre-industrial
aerosol (Tg)
Industrial aerosol (Tg)

Nd parametrization

Cloud cover parametrization
Forcing (Wm-2)
B&L
(1995)
0.34 Tg S
Sulphate: 0.44 Tg S
Various empirical
results
Le Treut and Li (1991);
Roeckner et al. (1991)
-0.5 to -1.4;
-0.5 to -1.5
Jones and
Slingo (1996)
0.16 Tg S
Sulphate: 0.3 Tg S
Jones et al. (1994b);
Hegg (1994); B&L (1995)
Smith (1990)
-1.5; -0.5; -0.6
Chuang et al.
(1997)
Sulphate: 0.25 Tg S,
Carbon aerosols:
1.72 Tg
Sulphate: 0.30 Tg S
Chuang and
Penner (1995)
NCAR-CCM1
-0.62 to -1.24
(internal mix);
-1.64 (external mix)
Feichter et al.
(1997)
Sulphate 0.3 Tg S
Sulphate: 0.38 Tg
B&L (1995)
Sundqvist et al.
(1989)
-0.76
Lohmann and
Feichter (1997)
   
B&L (1995)
Sundqvist et al.
(1989)
-1.0
Chuang et al.
(2000)
Sea salt: 0.79Tg,
Dust: 4.93 Tg,
Sulphate: 0.25 TgS,
Organic matter: 0.12 Tg
Sulphate: 0.30 TgS,
Organic matter: 1.4 Tg
BC: 0.19 Tg
Chuang and
Penner (1995)
 
-1.85 (all aerosols)
-1.51 (all carbon aerosols)
-1.16 (biomass
aerosols only);
-0.30 (sulphate only)
Kiehl et al.
(2000)
   
Martin et al. (1994);
Martin et al. (1994)
with N d minima;
Jones et al. (1994b);
B&L (1995)
Rasch and
Kristjansson
(1998)
-0.68; -0.40;
-0.80; -1.78
Rotstayn
(1999)
Sulphate: 0.21 TgS
Sulphate: 0.30
TgS
B&L (1995);
Roelofs et al.
(1998)
Smith, (1990)
-1.2; -1.7
Iversen et al.
(2000)
Sulphate: 0.14 TgS,
BC: 0.01 TgC,
Sea salt and dust included,
but not quantified
Sulphate: 0.60
TgS, BC: 0.25
TgC
Similar to
Chuang and
Penner (1995)
Rasch and
Kristjansson
(1998)
-1.36

Table 5.11b: Comparison of indirect forcing by different models with cloud amount and liquid-water path feedback.
Model
Pre-industrial
aerosol (Tg)
Industrial aerosol (Tg)

Nucleation
parametrization

Cloud cover parametrization
Forcing (Wm -2)
Lohmann and
Feichter
(1997)
Sulphate: 0.3 TgS
(interactive)
Sulphate: 0.38 Tg S
(interactive)
Boucher and
Lohmann (1995)
Sundqvist et al.
(1989);
Beheng (1994)
-1.4
Lohmann and
Feichter
(1997)
Sulphate: 0.3 TgS
(interactive)
Sulphate: 0.38 Tg S
(interactive)
Boucher and
Lohmann (1995)
Xu and Randall
(1996);
Berry (1967)
-2.2
Lohmann and
Feichter
(1997)
Sulphate: 0.3 TgS
(interactive)
Sulphate: 0.38 Tg S
(interactive)
Boucher and
Lohmann (1995)
Xu and Randall
(1996);
Beheng (1994)
-4.8
Lohmann et al.,
(2000a)
Monthly average
Sea salt: 0.79 Tg
Monthly average
Dust: 5.23 Tg
Interactive Organic
matter: 0.12 Tg
Interactive sulfate
Total interactive
sulphate: 1.04 Tg
Interactive organic
matter:1.69 Tg (tot)
Interactive black
carbon: 0.24 Tg
Chuang and Penner
(1995)
Sundqvist et al.
(1989);
Beheng (1994)
Total forcing:
-1.1 to -1.9
Carbon only:
-0.9
Sulfate only:
-0.4
Rotstayn
(1999)
Monthly average
Sulphate: 0.21 Tg S
Monthly average
sulphate: 0.30 Tg S
Boucher and
Lohmann (1995);
Roelofs et al. (1998)
Cloud cover;
Smith (1990)
-2.1; -3.2
Iversen et al.,
(2000)
Sulphatee: 0.14 TgS,
BC: 0.01 TgC,
Sea salt and dust included,
but not quantified
Sulphate: 0.60 TgS,
BC: 0.25 TgC
Similar to Chuang
and Penner (1995)
Rasch and
Kristjansson
(1998)
-1.9
Ghan et al.,
(2001b)
Sulphate: 0.42 TgS,
OC: 1.35 Tg,
BC: 0.22 Tg,
Sea salt: 4.3 Tg,
Dust: 4.3 Tg
Sulphate: 0.68 TgS
Abdul-Razzak and
Ghan (2000)
0 if unsaturated,
1 if saturated;
Ziegler (1985)
-1.7
Sulphate;
(2.8 °x2.8°)
Ghan et al.,
(2001b)
Sulphate: 0.39 TgS,
OC: 1.14 Tg,
BC: 0.18 Tg,
Sea salt: 3.8 Tg,
Dust: 4.6 Tg
Sulphate: 0.58 TgS
Abdul-Razzak and
Ghan (2000)
0 or 1;
Ziegler (1985)
-2.4
(4.5 °x7.5°)
Ghan et al.,
(2001b)
As above
As above
Abdul-Razzak and Ghan (2000)
0 or 1; modified
Tripoli and
Cotton (1980)
-3.2
(4.5 °x7.5°)

Continues on next page



Other reports in this collection