North American (Laurentian, Cordilleran and the Green- Satellite and
tide gauge
land), the northern European (Fennoscandia and the observations
Barents region) and the Antarctic ice sheets
3,7
. As the ice
3.1 ± 0.7 mm/yr
melted, starting around 20 000 years ago, sea level rose
Greenland Ice
Sheet
rapidly at average rates of about 10 mm per year (1 m per
0.2 ± 0.1 mm/yr
century), and with peak rates of the order of 40 mm per
Antarctic Ice
Sheet
year (4 m per century), until about 6000 years ago.
0.2 ± 0.4 mm/yr
Glaciers and
ice caps
The last few thousand years
0.8 ± 0.2 mm/yr
Sea level rose much more slowly over the past 6000
years. The sea level 2000 years ago can be deduced by
examining fish tanks built by the ancient Romans. Be-
cause the tanks had to be at sea level for the sluice gates
to function, one can precisely estimate sea level during
the period of their use. Comparison of this level with Ocean thermal
historical records indicates that there has been little net
expansion
1.6 ± 0.5 mm/yr
change in sea level from 2000 years ago until the start of
the 19th century
8
.
Changes in local sea level estimated from sediment
cores collected in salt marshes reveal an increase in the
rate of sea-level rise in the western and eastern Atlantic
Ocean during the 19th century and early 20th century
9–11
,
consistent with the few long tide-gauge records from Eu-
rope and North America
12
.
The last few centuries
Coastal and island tide-gauge data show that sea level
rose by just under 20 cm between 1870 and 2001, with
an average rise of 1.7 mm per year during the 20th cen-
tury and with an increase in the rate of rise over this pe-
Estimated contributions Observed
riod. This is consistent with the geological data and the to sea-level rise sea-level rise
few long records of sea level from coastal tide gauges
13

(Figure 6C.3). From 1993 to the end of 2006, near-glo-
2.83
±0.7
3.1
±0.7
mm/yr mm/yr
bal measurements of sea level (between 65°N and 65°S)
made by high precision satellite altimeters indicate glo- Figure 6C.4: Estimated contributions to sea-level rise from
bal average sea level has been rising at 3.1 ± 0.4 mm per
1993 to 2003 (uncertainty intervals are 5 to 95%).
year
14
. This rate is faster than the average rate of rise Source: Based on IPCC 2007
15
CHAPTER 6C ICE AND SEA-LEVEL CHANGE 157