Environmental Engineering Reference
In-Depth Information
Table 2. Estimated equilibrium climate response to increments in CO 2 or aerosols obtained by
taking differences between experiments defined in Table 1. The brackets in column no.2 define
the increments causing response. The numbers define levels or increments of CO 2 (ppm), whilst
aerosol levels or increments are defined by the letters PI (pre-industrial) and PD (present-day). In
the bottom row both CO 2 and aerosols are changed. Absolute changes are shown for temperature,
precipitation, cloud fraction, and liquid water path; relative changes are shown for atmospheric
life-time of aerosol species, both relative and absolute changes are shown for aerosol optical
depth (AOD). Rows 5 and 8 are associated with examples in Fig. 1
Δ
AOD
%
10 −3
Δ
LWP
g/m2
Δτ
SO 4
%
Δτ
BC
%
Δτ
POM
%
Δτ
SS
%
Δτ
DU
%
ΔT
K
ΔP
mm/d
ΔCl
10 −2
Experiment Increment
[PI - PD],
−30.06
1a)-1b)
2.09
0.178
0.63 −7.52 −11.4
0.9 −5.1 −3.3 −5.8
355
−39.3
[PI - PD],
−30.31
2a)-2b)
1.50
0.131
0.50 −2.29 −9.7 −0.4 −5.6 −3.0 −3.9
355
−41.9
[PI - PD],
−29.30
2c)-2e)
1.34
0.114
0.34 −2.83 −10.0
1.4 −3.8 −2.0 −4.4
710
−38.4
PD,
−1.72
1c)-1b)
1.99
0.113
0.65
1.69 −1.4 −1.9 −2.1 −1.7
0.3
[580-355]
−2.3
PD,
−3.45
2d)-2b)
2.06
0.120
0.66
3.39 −2.3 −1.7 −1.8 −3.8 −0.3
[580-355]
−4.8
PD,
−3.94
2e)-2b)
2.85
0.160
0.89
4.62 −2.0 −1.8 −2.1 −4.5
0.8
[710-355]
−5.4
PI,
−2.01
2c)-2a)
2.69
0.143
0.73
4.08 −2.4
0.0 −0.3 −3.5
0.4
[710-355]
−1.97
[PD, 580
38.54
2d)-2a)
0.56 −0.011
0.16
5.68
8.2 −1.3
4.0 −0.8
3.7
− PI, 355 ]
37.41
3. Concluding Remarks
In short we conclude as follows. (1) Whilst aerosol changes since PI largely
counteract the effects of CO 2 -increases, there are potentially important exceptions
for precipitation in the subtropics and in the southern extra-tropics. (2) Adding
an unaccounted cdnc-level strongly reduces the effects of aerosols on climate.
A pre-requisite for estimating climate effects of anthropogenic aerosols is therefore
that the natural conditions are accurately modelled. (3) A CO 2 -increase shortens
the atmospheric life-time of aerosols due to increased precipitation in major
aerosol emission regions. This life-time reduction is larger for present-day (PD)
aerosol emissions than for pre-industrial (PI). The aerosol cooling effect is thus
reduced by the CO 2 -increase as a feedback causing nonlinear reinforcement of the
CO 2 driven global warming.
 
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