Future prospects - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 354

over these 45 years was estimated to have averaged 1.7 0.2mm/yr, although the
curve showed periodic oscillations. Furthermore, the curve of sea level vs. time
seemed to be accelerating upward in the 1990s. In a more recent study, Holgate
(2007) chose nine long and nearly continuous sea level records from around the
world to explore rates of change in sea level for 1904-2003. The lack of high-
quality long-life gauge records was circumvented by finding representative gauges
that matched the data for 1952 to 1997 when more data were available. These
records were found to capture the variability found at a larger number of stations
over the last half-century which was studied in their 2004 paper. The addition of
new data not only extended the time period back to 1904 but also the time period
forward to 2003. The new results indicated that the apparent acceleration noted in
the 1990s tailed off and now appears to have been just another oscillation, while
the extended curve indicated that the rate of rise of sea level was slightly higher
early in the century than it was later in the century. According to Holgate (2007):
''Extending the sea level record back over the entire century suggests that the
high variability in the rates of sea level change observed over the past 20 years
were not particularly unusual. The rate of sea level change was found to be larger
in the early part of last century (2.03 0.35mm/yr 1904-1953), in comparison
with the latter part (1.45 0.34mm/yr 1954-2003). The highest decadal rate of
rise occurred in the decade centered on 1980 (5.31mm/yr) with the lowest rate of
rise occurring in the decade centered on 1964 ( 1.49mm/yr). Over the entire
century the mean rate of change was 1.74 0.16mm/yr'' (see Figure 11.15 ) .
Jevrejeva et al. (2008) found that sea level rise began well before large-scale
CO 2 emissions (see Figure 11.16 ) This would suggest that the relationship between
global warming and CO 2 emissions may be weak. According to this study, the
pace of sea level rise has oscillated about an upward trend line during the 20th
century even though a serious rise in sea level began near the beginning of the
19th century. The rate of sea level rise from 1992 to 2002 was the highest
recorded. This might suggest a relationship to CO 2 ; however, the rate of sea level
rise dropped from about 1955 to 1975.
According to Singer and Avery (2007) the initial rapid rise of sea level was
about 200 cm per century when the great ice sheets began to melt at the end of the
last period of glaciation. This gradually changed to a slower rate of rise (15-20 cm
per century) about 7,500 years ago, once the large ice masses covering North
America and North Europe had melted away. But the slow melting of the West
Antarctic Ice Sheet continued and will continue, barring another ice age, until it
has melted away perhaps 6,000 years from now. This means that the world will
continue to endure a sea level rise of about 18 cm per century (1.8mm per year),
just as it has been in previous centuries. What is more, it is likely that there is
nothing we can do about it. Thus, Singer and Avery (2007) attribute continuing
slow sea level rise to natural consequences of the post-glacial period but make no
allowance for anthropogenic global heating.