Emissions Scenarios - IPCC

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Scenario Driving Forces
the VOC Protocol of the UN Convention on Long-Range
Transboundary Air Pollution. However, for reasons similar to
those for NOj^, the cun'ent reduction of 11% with respect to
1990 levels and 15% with respect to 1987 levels suggests that
the plaimed reduction to 30% in 1999 may not be reached
(EEA, 1999). As a consequence, threshold values for ozone
continue to be exceeded in Europe.
No long-term global scenarios for emissions of NMVOCs and
CO were identified beyond IS92, which assumes increasing
emissions. The important role of biomass combustion in these
emissions means that a scenario with low carbon emissions
because of an increased used of biomass energy does not
automatically lead to low emissions of NMVOCs and CO.
Also, emissions trends are influenced significantly by
assumptions as to the type of combustion or other conversion
technology (e.g. gasification) deployed in the future. If
biomass fuel is used in modem large power plants or boilers, or
is to be converted into modem energy carriers, CO emissions
will be almost negligible compared to those of traditional uses.
As with sulfur, however, it seems plausible that with rising
incomes, abatement of the ozone precursors may be initiated in
non-OECD regions to address local and particularly regional
air pollution (photochemical smog). Since control of these
substances is more difficult than that of sulfur, it may not be
implemented until later.
3.6.6. Halocarbons and Other Industrial Gases
This category of GHG emissions comprises a wide basket of
different gas species that originate from a multitude of
processes. Generally, their common characteristic is that they
are released into the atmosphere in comparatively small
amounts, but on a molecular basis most of the gases are longlived,
with atmospheric lifetimes up to 50,000 years. Generally
they have a strong greenhouse forcing per molecule (see
Chapter 5, Table 5-7).
Anthropogenic emissions of gases that cause stratospheric
ozone depletion (chlorofluorocarbons (CFCs), hydrochlorofluorocarbons
(HCFCs), halons, methylchloroform, carbon
tetrachloride, and methylbromide) are controlled by
consumption restrictions (production plus imports minus
exports) in the Montreal Protocol. No special SRES scenarios
were developed for these gases because their future emission
levels (phase out) are primarily policy driven and hence
unrelated to scenario variations of important driving-force
variables such as population, economic growth, or industrial
output. Instead, the Montreal Protocol scenario (A3, maximum
allowed production scenario) from the 1998 WMO/UNEP
Scientific Assessment of Ozone Depletion is used
(WMO/UNEP, 1998).
The procedures for constructing scenarios for hydrofluorocarbon
(HFC), polyfluorocarbon (PEC), and sulfur
hexafluoride (SFg) emissions - for which there is an extreme
paucity of scenario literature - are based on Fenhann (2000)
and are described in greater detail in Chapter 5, Section 5.3.3.
In this approach, future total demand for CFCs, HFCs, and
other CFC substitutes is estimated on the basis of historical
trends. HFC emissions are calculated using an assumed future
replacement of CFCs by HFCs and other substitutes. The main
drivers for the emissions are population and GDP growth. The
sparse literature available (reviewed in Fenhann, 2000)
indicates that emissions are related non-linearly to these
driving forces, with important possibilities for saturation
effects and long-term decoupling between growth in driving
force variables and emissions. The emissions have been tuned
to agree with emissions scenarios presented at the joint
IPCC-TEAP expert meeting (WMO/UNER 1999). Material
from the March Consulting Group (1999) has also been used.
For PFCs (CF4 and C,Fg) the emissions driver is primary
aluminum production, which is generally modeled using GDP
and a consumption elasticity. Recycling rates are increasingly
important, as reflected in the SRES scenarios (see Chapter 5).
Aluminum production by the Soederberg process resulted, on
average, in the emission of 0.45 kgCF^ per tAl and 0.02 kgC2Fg
per tAl in 1998 in Norway. The effect of future technological
change on the emissions factor can be assumed to be large,
since the costs of modifications in process technology can be
offset by the costs of saved energy. A considerable reduction in
the emission factors has already taken place and the present
emission factor of 0.5 kgCF^ per tAl is expected to fall to 0.15
kgCF^ per tAl at various rates (see Chapter 5). An emission
factor for C^Fg, 10 times lower than that of CF^ was used in the
calculations. The present trend of not replacing CFCs and
HCFCs with high global warming compounds like PFCs (or
SF^) is also assumed to continue, which might underestimate
the effect of future emissions. The only other source included
for PEC emissions is semiconductor manufacturing, for which
the industry has globally adopted a voluntary agreement to
reduce its PEG emissions by 10% in 2010 relative to 1995
levels.
SFg emissions originate from two main activities - the use of
SFg as a gas insulator in high-vohage electricity equipment,
and its use in magnesium foundries, in which SFg prevents the
oxidation of molten magnesium. The driver for the former is
electricity demand and for the latter it is future magnesium
production, which will depend on GDP and a consumption
elasticity. Emission factor reductions over time that result from
more careful handling, recovery, recycling, and substitution of
SFg are assumed for both sources. Fenhann (2000) assumes
that in low future scenarios SFg emissions factors decline to
one-tenth their present values between 2020 and 2090. In high
future scenarios, Fenhann (2000) assumes reduction levels are
somewhat lower, ranging from 55% to 90% depending on the
region. In the absence of scenario literature, these assumptions
are retained here (see Chapter 5). Other applications of SFg
include as a tracer gas in medical surgery and the production of
semiconductors, and as an insulator in some windows.
However, these sources are assumed to be cause less than 1%
of the global emissions.