Take a look at Figure SPM-5 in the SPM - AOGCM projections of surface
temperatures. For the period 2020-29 there is very little difference
in projected temperature rise (from 1980-99) between the three
scenarios illustrated (B1, A1B, A2). The SPM says "Best-estimate
projections from models indicate that decadal-average warming over
each inhabited continent by 2030 is insensitive to the choice among
SRES scenarios, and is very likely to be at least twice as large as
the corresponding model-estimated natural variability during the 20th
century." My eyeball suggests that the rise is about 0.8C.
I'd like to explore some of the implications of this finding. It
suggests, for instance, that we have in effect got a "forecast" of
global average temperature change over the next 25 years. We're
committed to this warming whatever we do. From a policy perspective,
we therefore have a known challenge to meet (even if we don't/can't
know the full implications of that 0.8C). Adaptation is required, and
to enable us to plan effective adaptation, we will have to work on
refining projections (both regionally and globally) of near-term
(10-20 year) change. I know that some work is being done on using
AOGCMs as seasonal forecast tools at the Hadley Centre - but is this
seen as an important research focus? It strikes me that this is one
area with huge policy relevance.
Of course, this doesn't mean that we can afford to ignore mitigation.
The spread of the red curves (2090-99) in SPM-5 gives a good
indication of what early action on GHGs might achieve. Policies
designed to minimise warming by the end of the century are clearly
essential, but they're not the only game in town. Does the WG2 draft
reflect this? While the international political community focusses on
Kyoto-2, are we failing to prepare for the inevitable?
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