Estimating the Glacier Contribution to Sea-Level Rise for the Period 1800–2005
P. W. Leclercq
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J. Oerlemans
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J. G. Cogley
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J. G. Cogley Department of Geography, Trent University
, 1600 West Bank Drive, Peterborough, ON K9J 7B8,
Canada
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P. W. Leclercq (&) J. Oerlemans IMAU,
Utrecht University
, Princetonplein 5, 3584 CC Utrecht,
The Netherlands
In this study, a new estimate of the contribution of glaciers and ice caps to the sea-level rise over the period 1800-2005 is presented. We exploit the available information on changes in glacier length. Length records form the only direct evidence of glacier change that has potential global coverage before 1950. We calculate a globally representative signal from 349 glacier length records. By means of scaling, we deduce a global glacier volume signal, that is calibrated on the mass-balance and geodetic observations of the period 1950-2005. We find that the glacier contribution to sea-level rise was 8.4 2.1 cm for the period 1800-2005 and 9.1 2.3 cm for the period 1850-2005.
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Absolute change in global glacier volume (cm sea-level equivalent)
Exponent scaling length to volume
Cumulative contribution of glacier to sea-level change as determined by MB data
Cogley (2009) (cm)
Regression coefficients
Scaling exponents relating glacier thickness and width to glacier length
1 Introduction
There is abundant evidence that eustatic sea level has been rising for at least the past two
centuries (e.g. Church and White 2006; Jevrejeva et al. 2008; Cabanes et al. 2001; Warrick
and Oerlemans 1990; Barnett 1983). Although the uncertainties are significant, the general
view is that this rise has been between 15 and 25 cm for the period 18502000. This
number is based on the analysis of tide gauge data, which do not provide a very good
coverage of the oceans. Nevertheless, it appears that tide gauge and satellite data are
broadly in agreement (e.g. Nicholls and Cazenave 2010), lending some credibility to the
use of tide gauge data to infer sea levels further back in time. For the period 19932009,
high precision altimetry from satellites shows that sea level rose by 3.3 0.4 mm year-1
(Nerem et al. 2010). This suggests that sea level rise is accelerating.
Finding the causes for the current sea-level rise is crucial. Thermal expansion of ocean
water, changes in terrestrial storage of water, mass loss of ice caps and glaciers, and
possible long-term imbalances of the mass budgets of the Greenland and Antarctic ice
sheets have been listed as the most important processes contributing to the observed
sealevel rise. The pressure, both scientific and political, to make estimates of future sea-level
change has led to the use of so-called semi-empirical approaches in which a simple relation
between past sea-level rate and temperature or radiative forcing is determined, and then
extrapolated through the twenty-first century (e.g. Rahmstorf 2007; Grinsted et al. 2009;
Vermeer and Rahmstorf 2009). The uncertainties in such an approach are large and the
resulting potential errors in projections enormous. For instance, if a long-term contribution
from the Antarctic ice sheet to sea-level rise were to be erroneously attributed to the melt
of glaciers and ice caps, an empirically determined sensitivity parameter could be very
inaccurate. To constrain models in a better way, the processes that cause sea-level change
have to be quantified in the best possible way. In this paper we attempt to estimate the
contribution of glaciers and ice caps since 1800 AD. Throughout this paper we mean by
glacier contribution the contribution to sea-level change from all glaciers and ice caps
outside the large ice sheets of Greenland and Antarctica. Included are the glaciers and ice
caps on Greenland and Antarctica which are not part of or attached to the main ice sheets.
There are basically two approaches to estimate the loss of glacier ice over longer
periods of time. The first approach is to use modelled climate sensitivity of glacier mass
balance in combination with instrumental meteorological records of temperature and/or
precipitation. It is assumed that the glacierised area does not change, and that the effect of
climate change can simply be calculated by the combination of mass-balance sensitivity
and climate perturbations. This approach was applied by Zuo and Oerlemans (1997) to 100
glacierized regions, allowing for the fact that glaciers in different climatic settings have
different sensitivities. A major problem in this procedure is the definition of an initial state.
One cannot just assume that at a certain point in time the state of any glacier is in balance
with the prevailing climate. Zuo and Oerlemans (1997) showed that a difference (climatic
imbalance) of only 0.3 K between the real climate and the climate in which glaciers would
have been in equilibrium has a large effect on the calculated contribution to sea-level
change.
In the second approach one uses data on geometric changes of glaciers directly. This is
attractive, because climate data are not needed (...truncated)