Geoscience Reference
In-Depth Information
Table5.1
SummaryconclusionsoftheIPCC's1990,2001and2007assessmentsforforecasttemperatureandsea-level
changes1990-2100.Subsequentresearchsuggeststhatthesemaybelow,althoughthisisanareaofconsiderable
debate
2001 Several models,
2007 A2 (B-a-U)
1990 B-a-U above
all SRES envelope
scenario above
Change 1990-2100
pre-industrial levels
above 1990
1980-99 mean
Warming
High estimate
5.25
◦
C
5.8
◦
C
5.4
◦
C (A1F1 scenario
b
6.4
◦
C)
Best estimate
3.25
◦
C
2.0-4.5
◦
C (model
ensemble)
3.4
◦
C
Low estimate
1.8
◦
C
1.4
◦
C
2.0
◦
C (B1 scenario
c
1.1
◦
C)
Sea level
High estimate
a
110 cm
88 cm
51 cm (A1F1 scenario
b
59 cm)
Best or average
estimate
a
65 cm (best estimate)
22-70 cm (all models,
all SRES averages)
37 cm (A2 median
value)
Low estimate
a
23cm(B1scenario
c
18 cm)
22cm
9cm
a
Not including land-ice uncertainty and above 1990 level.
b
The A2 scenario is the 2007 scenario the IPCC used in their summary global warming graph. This
scenario is broadly analogous to the IPCC's 1990 B-a-U and does factor in some very modest climate
change policies. However, the 2007 assessment also includes the A1F1 scenario which is the scenario that
includes fast economic growth and more intense fossil fuel use. This is included in the table not just for
interest but because some reports and summaries by independent academics and science writers of the
2007 assessment (including the stop press appendix in this topic's first edition, published in 2007) quote
the 2007 IPCC report for 2100 warming of 1.1-6.4
◦
C and sea-level rise estimate as 18-59 cm.
c
The B1 scenario is one of low economic growth with global cooperation and is not considered business
as usual.
The IPCC applied a similar methodology in 2001 to sea-level rise. The seas are
expected to rise due to the melting of glaciers, the Greenland and Antarctic ice
caps and the thermal expansion of the oceans. Of these, thermal expansion is the
dominating factor and here much depends on the degree of heat transferred to the
oceans. Equally, there is uncertainty as to the rate of glacier and ice-cap melt. As
melting affects cold terrestrial systems, much of the subsequent sea-level discussion in
this topic on biological and human aspects will focus on this dimension, and also total
sea-level rise, as this affects terrestrial ecosystems lost due to marine encroachment.
(Readers will have to look elsewhere for detailed discussion on aspects of thermal
expansion.)
Antarctica
may
, however, offset part of this rise by trapping more ice from the
increased snow precipitation expected in a warmer world. However, while its 2001
best-estimate range for 1990-2100 warming essentially captured its 1990 best estim-
ate, the 2001 estimates for sea-level rise were lower (see Table 5.1). This was because
of improved computer models. The 2001 IPCC assessment refers to average SRES
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