Environmental Engineering Reference
In-Depth Information
mitigate climate change to this level, considerable reductions in CO
2
and
other greenhouse gases from the world's energy system are necessary. If
shale gas is to have a role in the world's energy system, it must be consistent
with existing mandates for the avoidance of dangerous levels of climate
change. This section describes the direct and indirect roles of shale gas in
the world's energy system and the associated changes in greenhouse gas
emissions that might be expected.
3.1 The Significance of the Energy System in Contributing to
Climate Change
Greenhouse gases, as defined by the Kyoto Protocol, include carbon dioxide
(CO
2
), methane (CH
4
), nitrous oxide (N
2
O), sulfur hexafluoride (SF
6
) and a
group of chemicals called hydrofluorocarbons (HFCs). There are other gases
that also trap heat, such as ozone and black carbon, however, it is the gases
controlled under the Kyoto Protocol that cause the dominant anthropogenic
influence on the atmosphere.
17
Of these Kyoto gases, CO
2
emissions dom-
inate, being responsible for 76.7% of global emissions in 2004, the main
source being fossil-fuel combustion, which was responsible for 56.6% of
global greenhouse gas emissions in the same year.
29
CO
2
emissions from
fossil-fuel combustion are also the fastest-growing source of GHGs globally,
increasing by 50% between 1990 and 2012,
29,30
with an average annual in-
crease during the last decade of 3%.
30
To successfully mitigate climate
change, addressing the dominant and growing amount of CO
2
from fossil
fuel combustion is essential. Thus the impact that shale gas exploitation has
on the climate is dependent on the role it plays in the wider energy system
and how it contributes towards emissions reductions from fossil fuel
combustion.
3.2 Cumulative Emissions and Climate Change
The challenge of global mitigation positions shale gas in the context of the
limits placed on the amount of greenhouse gas emissions that can be re-
leased this century while avoiding a 2 1C increase in global mean surface
temperature. When shale gas and other fossil fuels are burnt they release
CO
2
into the atmosphere, with some of the CO
2
being taken up by 'carbon
sinks' such as the oceans or vegetation, however, that which remains in the
atmosphere (45% of CO
2
emissions) remains there for over 100 years. Thus
CO
2
accumulates in the atmosphere and, as a greenhouse gas, traps heat.
The amount of global warming that can be expected has been demonstrated
to directly correlate with the accumulated amount of CO
2
in the atmos-
phere.
17,31
Consequently there is a great deal of analysis to estimate the
amount of 'cumulative emissions' or an 'emissions budget' that the at-
mosphere can hold without going beyond a 2 1C increase in global mean
surface temperature, or even higher.
31,32
The limit of cumulative emissions
that can be released into the atmosphere with a good probability of not
