Mark B. Dyurgerov

Glaciers dominate eustatic sea-level rise in the 21st century

Ice loss to the sea currently accounts for virtually all of the sea-level rise that is not attributable to ocean warming, and about 60% of the ice loss is from glaciers and ice caps rather than from the two ice sheets. The contribution of these smaller glaciers has accelerated over the past decade, in part due to marked thinning and retreat of marine-terminating glaciers associated with a dynamic instability that is generally not considered in mass-balance and climate modeling. This acceleration of glacier melt may cause 0.1 to 0.25 meter of additional sea-level rise by 2100.

Mass balance of glaciers and ice caps: Consensus estimates for 1961–2004

[1] Working with comprehensive collections of directly-measured data on the annual mass balance of glaciers other than the two ice sheets, we combine independent analyses to show that there is broad agreement on the evolution of global mass balance since 1960. Mass balance was slightly below zero around 1970 and has been growing more negative since then. Excluding peripheral ice bodies in Greenland and Antarctica, global average specific balance for 1961-1990 was -219 ± 112 kg m -2 a -1 , representing 0.33±0.17 mm SLE (sea-level equivalent) a -1 . For 2001-2004, the figures are -510 ± 101 kg m -2 a -1 and 0.77±0.15 mm SLE a -1 . Including the smaller Greenland and Antarctic glaciers, global total balance becomes 0.38 ± 0.19 mm SLE a -1 for 1961-1990 and 0.98 ± 0.19 mm SLE a -1 for 2001-2004. For 1991-2004 the glacier contribution, 0.77 ± 0.26 mm SLE a -1 , is 20-30% of a recent estimate of 3.2 ± 0.4 mm a -1 of total sea-level rise for 1993-2005. While our error estimates are not rigorous, we believe them to be liberal as far as they go, but we also discuss several unquantified biases of which any may prove to be significant.

Year-to-Year Fluctuations of Global Mass Balance of Small Glaciers and Their Contribution to Sea-Level Changes

We estimate the means and the interannual variability during the last 30 yr of the mass balances of the small glaciers of the world (all glaciers except for the two large ice sheets), as well as the influence of these mass balance changes on fluctuations of sea level and their relation to climate. The mass balance data base was enriched by data for glaciers of the Arctic islands, Antarctica, and mountainous areas of Siberia, Central Asia, and the Caucasus, which have not been included in previous compilations. We also use a new estimate of the total area for the small glaciers on Earth: 680 X 103 km2. The global mean mass balance as a function of time was calculated three ways: the arithmetic mean for all glaciers (Gb,), arithmetic mean for a group of representative glaciers with longterm mass balance records (Gb2), and an area-weighted mean (Gb3). The last was calculated for seven large regions in order to estimate the contribution of small glaciers to sea-level change more precisely. The results include the following: * Gb, and Gb2 show good correlations with each other and with global air temperature anomalies, with correlation coefficients around 0.90.

Mass Balance of Mountain and Subpolar Glaciers: A New Global Assessment for 1961-1990

The goals of this article are (1) to combine published and unpublished mass balance measured data on more than 200 glaciers, check the quality of the data, digitize, and compile these for the period from the end of World War II (1945) to 1993 (with emphasis on the 1961-1990 period), and (2) to perform a review and analysis of this compilation. A simple global average mass balance for this period is -164 mm yr-1 (totaling -4.9 m) in water equivalent, not including iceberg calving. There are only about 40 glaciers with continuous mass balance measurements for more than 20 yr, but more than 100 with 1 to 5 yr of mass balance records. The glaciers under mass balance study differ in size from very small mountain cirque glaciers (less than 1 kin2) tO large valley glaciers (several hundred square kilometers) and subpolar ice caps with an area of several thousand square kilometers. Continuous and long-term mass balance measurements have been carried out mostly on middle-size glaciers with several exceptions. There are no longterm mass balance measurements in the following size classes: from 2-6 to 2km2; 28 to 210; and above 212 km2. The area of these unmeasured size classes of glaciers is about 200 x 103 km2, or about 29% of the global glacier area. The glacier area of mountain and subpolar glaciers (including local glaciers around Greenland and Antarctica ice sheets) is taken to be about 680 x 103 km2. The reduction in global glacier area due to retreat is calculated as 6-8 x 103 km2 from 1961-1990.

Mountain and subpolar glaciers show an increase in sensitivity to climate warming and intensification of the water cycle

The time-series of all available records of seasonal and annual glacier mass balances, equilibrium line altitude, accumulation area ratio and change in surface area of about 300 glaciers have been compiled, digitized, quality checked and analyzed over the period of almost four decades (1961–1998). These time-series show significant changes towards loss in glacier area and volume in global scale with accelerated rate, especially since the end of 1980s. The remarkable feature in this change is the increase of both winter and summer balances, which implies that glaciers are intensifying the water cycle in time of global warming. The sensitivity of glacier mass balance in regard to temperature and precipitation has also increased which resulted in an increase of glacier contribution to sea level rise from 0.15 mm/yr in 1961–1976 (10% of total sea-level rise) to 0.41 mm/yr in 1988–1998 (27% of total sea-level rise). Glacier contribution to the ocean has the potential to grow due to increasing snow accumulation and involving into the water cycle larger areas of individual glaciers around the Antarctic ice sheet.

Variability in Winter Mass Balance of Northern Hemisphere Glaciers and Relations with Atmospheric Circulation

An analysis of variability in the winter mass balance (WMB) of 22 glaciers in the Northern Hemisphere indicates two primary modes of variability that explain 46% of the variability among all glaciers. The first mode of variability characterizes WMB variability in Northern and Central Europe and the second mode primarily represents WMB variability in northwestern North America, but also is related to variability in WMB of one glacier in Europe and one in Central Asia. These two modes of WMB variability are explained by variations in mesoscale atmospheric circulation which are driving forces of variations in surface temperature and precipitation. The first mode is highly correlated with the Arctic Oscillation Index, whereas the second mode is highly correlated with the Southern Oscillation Index. In addition, the second mode of WMB variability is highly

Analysis of Winter and Summer Glacier Mass Balances

Seasonal mass balance components b w (winter balance) and b s (summer balance) as well as c t (total accumulation) and a t (total ablation), can be used directly to infer climate variables. In contrast, a c (net balance of the accumulation area) and a a (net balance of the ablation area), and b a or b a (annual or net balance) can not. The traditional Alpine system of observations of a c and a a , however, can be converted to true seasonal values b w and b s if both pairs of components are simultaneously observed for some years, because a correlation between the two pairs of components exists. We analyzed b w and b s data and their mean, standard deviations and ratios of these to the corresponding net or annual balances for 50 glaciers with relatively long records representing different regions in the northern hemisphere. We also investigated correlations between seasonal components. A negative correlation between b w and b s exists at many glaciers. About two-thirds of the glaciers show insignificant correlations (-0.3<r<0.3), implying independence of summer and winter balances. In a few unusual cases the correlations are positive. These different correlations, or lack thereof, may offer insight into feedback conditions that must exist in this climate-related system. The correspondence of the b w and c t and b s and a 1 , appears to depend largely on the relative amounts of summer snowfall, a function of their climatic environment expressed as a [α=(b w + b s )/2]. The contribution of variability of b s to the net balance increases markedly with decreasing values of α. The variability of b w and b s , and therefore the net balance, has been increasing with time; whether this is due to an increase in climate variability or to other causes is not clear. It appears that b w has been increasing with time at the highest altitudes, but b s has been increasing more rapidly especially at low altitudes; the many-glacier average net balance is becoming more negative.

Mountain Glaciers at the End of the Twentieth Century: Global Analysis in relation to Climate and Water Cycle

Abstract This work presents historical data on glacier mass balance. Until now, these data have been scattered throughout many publications, limiting their utility in the geosciences. The main objective of this contribution is to summarize data available in the digital data base of Dyurgerov (2002), and to discuss in some detail their quality and limitations. This paper is intended for glaciologists, climatologists, hydrologists, and other specialists interested in high-mountain and polar environments. Other potential users include those interested in the state of modern glaciers, their change on a global scale, or in changes occurring in any particular region.

Correlations between glacier properties: finding appropriate parameters for global glacier monitoring

To develop new strategies for global mass-balance monitoring, data for the period 1961-90 have been compiled for 80 glaciers with a variety of mass-balance and morphological parameters. This dataset is significantly larger than that used in previous studies. This allows us to check the mass-balance data for both strong and weak correlations with different glacier parameters. In many cases, the strong correlations suggest new approaches to monitoring glaciers on a global scale. For example, the mass balance at the terminus is strongly correlated with the difference in clevation between the terminus and the glaciers mean clevation. These casily measured parameters could be particularly useful in assessing maximum ablation and meltwater potential based on altitudes derived from maps and photographs. Good correlations also exist between differences in mass-balance parameters e.g. net balance minus terminus balance) and several other morphological properties (e.g. clevation range and length ). Equally important, the weak correlations demonstrate that some relationships commonly used on individual glaciers are not appropriate whe considering global monitoring strategies. For example, the correlation between net mass balance and terminus balance is very poor. Likewise, the correlation between the net mass balance and equilibrium-line altitude is weak, and the correlation between the net mass balance and activity index is almost non-existent. This suggests that although these elimatically sensitive parameters may be closely related on individual glaciers, these same relationships are not reliable as tools for monitoring glaciers on a global scale.

Characteristic mass-balance scaling with valley glacier size

Previous work on the relation between glacier volume and area and on accumulation area ratios suggests that balance rates measured at the glacier terminus are not constant or random from glacier to glacier but instead scale with glacier length. Using mass-balance data from a collection of 68 valley and cirque glaciers, we show that the terminus mass-balance rate scales roughly linearly with surface area and scales with length raised to an exponent constrained to fall roughly between 0.5 and 2 with 1.7 preferred if a glaciers length is dependent on the mass-balance conditions (rather than balance being dependent on length). When these exponents are used to predict valley-glacier volume-area scaling, the results are very close to empirical volume-area observations. Although the data are noisy and the proposed fits could be modified by improved observations, the scaling trend for terminus balance vs length remains clear. Although the exact value of the scaling exponent is not well determined, establishing the existence of this scaling relation will be important for studies of climate change and the impact of glacier recession on sea level.