Environmental Engineering Reference
In-Depth Information
The equilibrium thermal and hydrological responses to the total aerosol effects
(i.e., direct, semi-direct and indirect effects) are studied in a version of the GFDL
AM2.1 atmosphere general circulation model (AGCM) that includes a prognostic
treatment of aerosol-cloud interactions (Ming et al., 2007), coupled to a mixed
layer ocean model (Ming and Ramaswamy, 2009). The pre-industrial to present-day
increases in aerosols lead to a substantial reduction in the global mean surface
temperature (1.9 K), with the strongest cooling over the Northern Hemisphere
mid- and high latitudes (
Fig. 5a
). This is accompanied by a significant reduction in
precipitation north of the equator, and an increase to the south
(Fig. 5b)
. The
combined response to aerosols and radiatively active gases (i.e., greenhouse gases)
deviates considerably from the linear addition of the individual responses when
aerosol indirect effects are included. The results indicate that the large shift in
tropical precipitation is driven primarily by the spatially non-uniform aerosols.
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
6
(a)
(b)
AERO
AERO
GAS
BOTH
AERO+GAS
GAS
BOTH
AERO+GAS
4
2
0
-2
-4
90S
60S 30S
0
30N 60N 90
30S 20S 10S
0
10N 20N 30N
Fig. 5.
Zonal mean differences (present - pre-industrial) in (a) surface temperature (K) and (b)
precipitation (mm day
−1
) in response to aerosols (AERO), radiatively active gases (GAS) and
both (BOTH). For reference is the arithmetic sum of AERO and GAS. Figure is from Ming and
Ramaswamy (2009)
3. Influence of Climate Change on Surface O
3
Observational analyses indicate that weather strongly modulates ambient surface
O
3
levels from day to day, with many techniques developed over the past decades
to remove this influence in order to evaluate the success of O
3
abatement strategies
(e.g., Porter et al., 2001). The number of high-O
3
events can vary by as much as a
factor of 10 from year to year, largely driven by fluctuations in meteorology
(Leibensperger et al., 2008). Of all meteorological variables, temperature typi-
cally correlates most strongly with high-O
3
events (e.g., Jacob and Winner, 2009).
This correlation largely reflects three key processes: ventilation of surface air,
with higher temperatures associated with stagnant air (e.g., Jacob et al., 1993);
local O
3
production chemistry, in particular the thermal dependence of PAN
decomposition (e.g., Sillman and Samson, 1995); temperature-sensitive biogenic
emissions, most notably isoprene (e.g., Guenther et al., 2006). Increases in other
emissions such as wildfires and air-conditioning use in response to higher tempe-
ratures may further amplify the O
3
response. Other meteorological changes in a
warmer world (e.g., convective activity, cloud distributions, humidity, mixing depths)
might act as a negative feedback (e.g., Jacob and Winner, 2009 and references
