SODBatch A&B SPM Comments co-chair response final ... - ipcc-wg3

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Comments
IPCC WGIII Fourth Assessment Report, Second Order Draft
(Government of Spain)
A 5 1 5 6 To be accurate, I believe that this should read, "…it is technically
feasible to stabilise GHG concentrations in the atmosphere, even at
levels below 450 ppmv CO2 eq, provided that…" I believe that a
significant percentage of the 16 studies reviewed in this 'band' are
scenarios for concentrations of less than 450 ppmv CO2eq.
(Steve Sawyer, Greenpeace International)
A 5 1 0 5 This wording suggests that stabilisation below 450ppmv CO2-eq is
not feasible; if so, this crucial constraint should be explicitly stated
and defended here as well as in the body of the report. The
wording also suggests that 450ppmv is "low": it is low only in
relative terms when compared with a selected range of higher
potential stabilisation levels; it is not low when compared with preindustrial
concentrations. The failure to mention lower stabilisation
levels such as returning to pre-industrial levels represents an
unexplained gap and potentially an artificially truncated range of
policy options.
(Stephen Sheppard, University of British Columbia)
A 5 1 5 4 For stabilization "as low as 450 ppm CO2-equivalent", emissions
almost certainly need to peak much sooner than just "within the
next few decades."
(Paul Baer, EcoEquity)
A 5 1 6 1 The statement that lower stabilisation requires earlier peaking of
emissions is only correct if one assumes certain constraints on the
stabilisation pathway. Theoretically, one could overshoot to
1000ppm and still stabilise at 400ppm equivalent a few hundred
years later, eg through a widespread development of bioenergy plus
CCS in the 22nd and 23rd centuries. Footnote 3 says that overshoot
pathways are designed to keep global mean temperature below the
eventual equilibrium level. This (subjective!) constraint on
Expert Review of Second-Order-Draft
Confidential, Do Not Cite or Quote
Response suggested by cochairs
TIA; heading text to be deleted,
but wording to be used for
merging with para 6
TIA; heading text to be deleted,
but wording to be used for
merging with para 6
TIA; heading text to be deleted,
but wording to be used for
merging with para 5, check with
new table 1.
TIA; heading text to be deleted,
but wording to be used for
merging with para 6
Suggestions to be taken up in
TS and ch 3
Action
for
chapter
Considerations
by the writing
team
TS, 3 accept. Text to
be revised
(3)
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