How might sea level
be affected by changes in the Arctic land ice?
Roger Barry
Professor of Geography and Director, National Snow and Ice
Data Center (NSIDC) and World Data Center (WDC) for Glaciology,
Boulder
Sea level change is driven by: the thermal expansion/contraction
of sea water in response to warming/cooling of the ocean;
additional runoff to the oceans from the melting of ice
sheets and glaciers; and from changes in ground and surface
water storage associated with consumptive use for agriculture,
industrial production and human consumption.
It is estimated that sea level rose by 1 to 2 mm/yr during
the twentieth century. Thermal expansion accounts for about
half of this increase and land ice melt, mostly from mountain
glaciers, about 20 to 25 percent. The contributions from
changes in ice volume in Greenland and the Antarctic are
uncertain, even as to sign of the change for Antarctica.
(The Antarctic and Greenland ice sheets hold the majority
of the earth's ice: an amount equivalent to 80 m of sea
level). There is also considerable uncertainty in the sign
of the change attributed to terrestrial water storage in
reservoirs and aquifers.
The largest contributions of meltwater are from shrinking
mountain glaciers and ice caps. Over the period 1901–1962,
contributions to sea level rise from glaciers in southern
Alaska-northwestern Canada, central Asia including the Himalayas,
and the southern Andes were estimated to be about 34, 16
and 12 percent of the total land ice contribution to sea
level rise, respectively (Haeberli, 1998). A further 10
percent may have derived from the Arctic islands of North
America and Eurasia, with the remainder coming from glaciers
in other regions. This regional balance of glacier meltwater
contributions to sea level change appears to have shifted:
Dyurgerov and Meier (1997) report a loss of 512 km-squared
area of ice from glaciers in Svalbard and 832 km-squared
area from the Arctic islands over the period 1961 through
1993. These amounts represent 43 percent of the total ice
loss in the northern hemisphere over the 32 year-period.
(Note that 400,000 km-squared area of ice represents 1m
of global sea level.)
References
Dyurgerov, M .B. and M. F. Meier. 1997. Year-to-year fluctuation
of global mass balance of small glaciers and their contribution
to sea level changes. Arctic and Alpine Research 29(4):392–401.
Haeberli, W. 1998. Historical evolution and operational
aspects of worldwide glacier monitoring. In Into
the Second Century of Worldwide Glacier Monitoring: Prospects
and Strategies, Haeberli, Hoelzle, and Suter, eds.
UNESCO, p. 35–51.
Dowdeswell, Julian A., et al. 1997. The mass balance of
circum-Arctic glaciers and recent climate change. Quaternary
Research 48 :1–14;
Dyurgerov, M. B., Meier, M. F. 1997. Mass balance of mountain
and subpolar glaciers: a new global assessment for 1961–1990.
Arctic and Alpine Research 29(4) :379–391
 
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