Emissions Scenarios - IPCC

Emission Scenarios 269
technically possible to reduce the anode emissions by a factor
of 10 (EU, 1997). This technically feasible reduction can be
achieved by changing from the Soderberg cells currently in use
to more modern pre-bake cells. It is assumed that this will
happen in the Al and Bl family scenarios, in which specific
emissions of 0.15 kgCF^/t are achieved by 2040 in the
OECD90 region and by 2090 in the other regions. In the A2
and B2 family scenarios the same specific emissions are
achieved later in the century in the OECD90 region and not
until after 2100 in the other regions.
PFCs are consumed in small amounts in such sectors as
electronics (tracers), cosmetics, and medical applications.
However, the only emissions included in Fenhann (2000)
beyond aluminum production were PFCs (as CF^) from
semiconductor production. In all SRES scenarios the emission
estimates used are those given by Hamisch et al. (1999) of 0.3
kt CF4 per year in 1990, 1.1 ktCF^ in 2000, 1.0 ktCF^ in 2010,
and constant thereafter. The use of these estimates reflects the
voluntary agreement, in April 1999, of the World
Semiconductor Council, which represent manufacturers from
Europe, Japan, Korea, and the US, among others. According to
this agreement, manufacturers have adopted the emission
reduction target for PFCs of 10% absolute reduction from 1995
emission levels by 2010. This target encompasses over 90% of
the total semiconductor production (WMO/UNEP, 1999). The
total PEC emissions in the four SRES scenario families cover
a range from 24 to 97 kt PFC in 2100 (Table 5-8; Fenhann,
2000).
5.4.3.3. Sulfur hexafluoride
SFg is an extremely stable atmospheric trace gas. All studies
concur that this gas is entirely anthropogenic. Its unique
physico-chemical properties make SFg ideally suited for many
specialized industrial applications. Its 100-year GWP of
23,900 is the highest of any atmospheric trace gas. In 1994,
atmospheric concentrations of SFg were reported to rise by
6.9% per year, which is equivalent to annual emissions of
5,800 tSFg (Maiss et al, 1996).
According to several sources (Kroeze, 1995; Maiss et al,
1996; Victor and MacDonald, 1998), about 80% of SFg
emissions originate from its use as an insulator in high-voltage
electrical equipment. The remaining 20% of the present global
SFg emissions (1200 tons per year) are emitted from
magnesium foundries, in which SFg is used to prevent
oxidation of molten magnesium. The global annual production
of magnesium is about 350,000 tons (US Geological Survey,
1998), and developing countries account for about 15% of the
total. SFg is also used to de-gas aluminum, but since SFg reacts
with aluminum, little or no atmospheric emissions result from
this process.
Major manufacturers of SFg agreed voluntarily to co-operate
on the compilation of worldwide SFg sales data by end-use
markets. Six companies from the US (three), Japan, Italy, and
Germany participated in the data survey. The companies do not
expect the total sales for magnesium foundries to increase
before 2000 (Science & Policy Services Inc., 1997). Based on
this information, the 1996 statistical production values were
used for the year 2000 in the fomiulation of the scenarios
reported in Fenhann (2000). Future production was projected
assuming the same consumption elasticity to GDP as for
aluminum (see discussion above). In 1996, about 41% of the
world magnesium was produced in the US; of this, only 16%
was processed in foundries for casting that resulted in
emissions of SFg (Victor and MacDonald, 1998). Since the
distribution of world foundry capacity appears to be roughly
similar to that of world magnesium production, Fenhann
(2000) assumes that, presently, 16% of the produced
magnesium is processed in foundries across all regions.
Relating this amount of the processed magnesium to the
aforementioned emission of 1200 tSFg per year yields an
emission factor of 21 kgSFg per ton of magnesium processed in
foundries. The demand for magnesium in automotive
applications as a strong lightweight replacement for steel is
growing quickly. Hence, it is expected that the fraction of total
magnesium production processed in foundries by 2050 will
grow to between two to three times the present level.
As mentioned above, no less than 80% of SFg emissions (or
4600 tons of SFg per year at present) originate from the use of
SFg as a gaseous insulator in high-voltage electrical equipment.
The unique ability of SFg to quench electric arcs has enabled
the development of safe, reliable gas-insulated high-voltage
breakers, substations, transformers, and transmission lines. The
demand for such electrical equipment is assumed to grow
proportionally to electricity demand (Victor and MacDonald,
1998; Fenhann, 2000) with an emission factor of 132.6 tSFg/EJ
electricity. Fenhann (2000) used preliminary electricity
generation projections from the four SRES marker scenarios
and assumed additional various other potentials for emission
reductions that result from more careful handling, recovery,
recycling, and substitution of SFg. Reduction rates vary in the
different SRES scenario storylines; the detailed assumptions
are reported in Fenhann (2000). The SFg emissions for the four
scenarios given in Fenhann (2000) range from 7 to 25 ktSFg in
2100. The main driver is electricity consumption, since the
bulk of emissions originate from electric power transmission
(for transformers).
SFg is also emitted from other minor sources, but for the
purposes of this report it is assumed that uncertainty ranges
factored into the alternative scenario formulations cover the
emissions from these sources.
5.5. Aerosols and Ozone Precursors
In addition to the GHGs discussed above, aerosol particles and
tropospheric ozone also change the radiative balance of the
atmosphere, albeit in a spatially heterogeneous manner. Sulfate
aerosol particles, which form as a consequence of SOj
emissions, act as a cooling agent. Their net effect is quite
uncertain, but is thought to offset the forcing from all ПОП-СО2