Geoscience Reference
In-Depth Information
Figure 24.1
Multimodel mean changes in surface air temperature (
◦
C, left), precipitation (mm/day, middle) and sea-level pressure
(hPa, right) for December to February (DJF, top) and June to August (JJA, bottom). Changes are given for the SRES A1B scenario,
for the period 2080-2099 relative to 1980-1999. Stippling denotes areas where the magnitude of the multimodel ensemble mean
exceeds the intermodel standard deviation (after Meehl
et al.
, 2007).
of soil moisture and runoff is a widespread feature of arid
zones, although there is consistency between the models
only in some regions, notably the Mediterranean, south-
western USA and parts of South America.
Sea-level rise could lead to dramatic changes to sabkhas
in arid regions such as the Arabian Peninsula. Global mean
sea-level rise projections from the IPCC AR4 are shown
in Table 24.2. The sea-level rise estimates comprise four
components: thermal expansion (calculated from the cli-
mate models, specifically the ocean component), glaciers
and ice caps excluding the Greenland and Antarctic ice
sheets (computed from a simple empirical formula that
links the global mean temperature to mass loss based
on observed data from 1963 to 2003), ice sheet surface
mass balance (computed from an ice sheet surface balance
model with snowfall amounts and temperature computed
from a high-resolution model scaled to the coupled mod-
els) and dynamical imbalance (computed from extrapola-
tion of observed rates from 1993 to 2003 and contributing
up to 0.7 mm during this period). The range shown in
Table 24.2 does not include uncertainties resulting from
climate-carbon cycle feedback or changes in ice sheet
flow (including dynamical processes). They do include a
component due to increased ice flow from Greenland and
Antarctica at the rates observed for 1993-2003.
Since IPCC AR4, there have been a number of stud-
ies that conclude that the sea-level rise by 2100 could
exceed 100 cm. Rahmstorf
et al.
(2007) note that since
1990 the observed sea-level has been rising faster than
the rise projected by models, as shown both by a recon-
struction using primarily tide gauge data and, since 1993,
by satellite altimeter data. The satellite data show a lin-
ear trend of 3.3
Figure 24.2
Multimodel mean changes in total cloud area
fraction (percent cover from all models). Changes are given
as annual means for the SRES A1B scenario for the pe-
riod 2080-2099 relative to 1980-1999. Stippling denotes
areas where the magnitude of the multimodel ensemble
mean exceeds the intermodel standard deviation (after Meehl
±
0.4 mm/yr (1993-2006) and the tide
gauge reconstruction trend is slightly less, whereas the
IPCC projected a best-estimate rise of less than 2 mm/yr.
Vermeer and Rahmstorf (2009) propose a simple relation-
