Geoscience Reference
In-Depth Information
Figure 13.20
Estimates of the contributions to global sea-level change for the period 1961-2003 (blue)
and 1993-2003 (red). Also given for each time period are the sum of the individual components, the
observed sea-level change, and the difference between the sums and observations. The bars represent
the 90 percent error range.
Source:IPCC (2007). Reproduced by permission of the IPCC (ch. 4, Observations: Oceanic climate change and sea level, Report
of WG1 1, IPCC, p. 419, fig. 5.21).
Figure 13.21
shows the time series of sea-level
in the past and projected through the twenty-first
century from the IPCC models using the A1B
emissions scenario. Relative to the 1989-1999
mean (the zero line on the y axis), sea-level by the
year 2100 is expected to have risen by 200 to 500
mm. Many uncertainties remain. The key wild
card is the behavior of the ice sheets. Recent
finding suggest that the IPCC estimate of sea-level
rise is too low because effects of changing ice
dynamics in Greenland and Antarctic leading to
accelerated iceberg discharge have not been taken
into account. There is an outside possibility that
a rise in sea-level might cause the West Antarctic
ice sheet to be buoyed up and melt bodily (not just
around the edges, as in the past) and cause a
further catastrophic sea-level rise but spread over
several hundred years.
3 Snow and ice
The effects of twentieth-century climate change
on global snow and ice cover are apparent in many
ways, but the responses differ widely as a result of
the different factors and timescales involved. Snow
cover is essentially seasonal, related to storm
system precipitation and temperature levels. Sea
ice is also a seasonal feature around much of the
Antarctic continent (see
Figure 10.35A
), but the
Arctic Ocean holds part of its sea ice cover
throughout the year. This is known as multiyear
ice as it has survived at least one summer melt
