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Control of greenhouse gas concentrations implies eventual limitations on
energy-related emissions
Energy is the single largest source of GHG emissions. It is responsible for
approximately 80% of net carbon emissions to the atmosphere. While net emissions
of carbon are associated with fossil fuel combustion, the carbon-to-energy ratio
varies between high-carbon fuels, such as coal, and low-carbon fuels, such as
CH4, approximately by a factor of two. Technologies such as hydroelectric
power, nuclear fission, wind power, and solar power are generally treated as
if they have little or no direct carbon emissions, though this may not be the
case. For example, CH4 may be released in the process of creating
a hydroelectric facility and carbon may be released in the manufacture of cement
used in nuclear power reactors. Technologies do exist that can biologically
sequester or physically remove and store carbon. Thus, in principle, controlling
energy-related carbon emissions is possible for several sources of carbon emissions
without foregoing fossil fuel use. These technologies are discussed in Chapter
3.
Narrowly defined technological solutions are unavailable, but a broad development
and deployment of technology is key to controlling the cost of emissions limitation
Emissions of GHGs are associated with an extraordinary array of human activities.
CO2 emissions are associated with the combustion of fossil fuels
and changes in land-use. They are thus affected by activities that range from,
for example, household heating and cooling to commercial lighting and appliances,
to the transportation of goods and provision of services, to the manufacture
of materials, to the growth and harvest of crops, and to the generation of electric
power. As a consequence, GHG emissions are greatly affected by other exogenous
and non-climate-policy factors. Narrowly defined technological solutions, such
as were available to address the problem of stratospheric ozone depletion, are
impossible for the climate issue. While no single technology provides a complete
solution to the problem of controlling emissions of GHGs, a significant set
of existing, emerging, and potential technologies is available to mitigation
climate change, as discussed in Chapters 2, 3
and 42.
Policy interactions will be significant
Future emissions depend to a large degree on the rate and direction of technological
developments in a broad array of human endeavours. For example, China’s
policies to stabilize its population size, taken for reasons unrelated to climate
change, will have a profound effect on Chinese emissions of GHGs to the atmosphere.
Policies to control non-GHG air pollutants can greatly affect GHG emissions.
For example, measures to substitute natural gas and non-carbon-emitting energy
forms, such as solar and nuclear power, for coal in electricity generation to
control local and regional air pollution can affect GHG emissions as well. On
the other hand, some policies that reduce local air pollution, such as scrubbing
power plants for sulphur, can reduce power-plant efficiency and increase GHG
emissions.
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