Geology Reference
In-Depth Information
Table 10.4 Composition of the crepuscular and sta-
bilised atmosphere on a dry basis (vol. %) (Valero
et al., 2011)
Crepuscular atmosphere
Component
BAU-I
BAU-II
A2-II
N
2
78.08
O
2
20.920214
20.66834
20.662
Ar
0.93
CO
2
0.068286
Other
0.0015
Stabilised atmosphere
Component
BAU-I
BAU-II
A2-II
N
2
78.08
O
2
20.94459
20.66835
20.662005
Ar
0.93
CO
2
0.04391
Other
0.0015
result in higher temperature increases than the BAU-I, which leads to a greater un-
certainty of predictions, since under these conditions one is more likely to experience
stronger non-linear feedbacks (perturbations) of the climatic system (Schneider,
2004).
Summarising, the crepuscular atmosphere occurs once all fossil fuel resources
have been depleted, which according to scenario BAU-I is set to be reached in
approximately 2200 with an atmospheric injection of about 2,000 GtC. Accordingly,
the crepuscular atmosphere has a carbon dioxide content of 683 ppm, a mean surface
temperature of 17
o
C (peak carbon dioxide induced warming of 3.7
o
C above pre-
industrial temperatures), a pressure of 1.021 bar and a composition, on a volume
basis of 78.8% N
2
, 20.92% O
2
, 0.93% Ar and 0.0015% of trace gases.
10.3.2 The crepuscular hydrosphere
Combustion of fossil fuels and other human activities affect the hydrosphere, which
can be modified by climate change, with the increased atmospheric temperature
causing ice melt, an alteration in the atmospheric water content and the modifi-
cation of precipitation patterns amongst others. In addition, many non-climatic
drivers such as land use change, reservoir management, pollutant emissions, water
and wastewater treatment may impact freshwater supply, a vital component of the
global hydrosphere. Indeed freshwater is expected to suffer an increase in nitrogen,
phosphorus, sulphates, heavy metals and organic content especially as the world's
population grows (Bates et al., 2008). Also worthy of note is the runoff from rivers
and surface heat as both affect the thermohaline circulation. They may also, albeit
indirectly, significantly influence atmospheric carbon dioxide concentrations (given
that the solubility of CO
2
in water is related to temperature). Changes in tem-
perature then affect the world water budget and this in turn affects the Earth's
temperature with the mean surface temperature influenced by the amount of green-
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