Gravity change on a glacier surface is a composite of several effects (e.g. melting and accumulation of snow and ice, redistribution of mass with depth by refreezing of meltwater and height and thickness changes of the snow and ice layers). Models and equations necessary to estimate the measured gravity change due to different effects are presented, and the propagation of observational errors is evaluated. The paper presents experiences with ground-based gravity measurements carried out on Hardangerjøkulen, Norway, in spring and autumn 2007. It was found that the vertical gradient of gravity contributes most to the uncertainty in the determined mass change. With present instrumentation, gravity can be measured with the required accuracy to determine the mass loss to ∼10% of the loss determined by conventional mass-balance measurements. Improvements in field procedures to achieve the required accuracy for measuring the mass/density changes directly, combining gravity measurements and GNSS (Global Navigation Satellite Systems), are discussed.

Temperature and precipitation data from three weather stations in the St Elias Mountains of Alaska and northwestern Canada were used to drive one-dimensional (1-D) (elevation-dependent) and 0-D degree-day mass-balance models. Model outputs were optimized against a 10 day resolution time series of mass variability during 2003–07 obtained from Gravity Recovery and Climate Experiment (GRACE) mass concentration (mascon) solutions. The models explained 52–60% of the variance in the GRACE time series. Modelled mass variations matched the phase of the GRACE observations, and all optimized model parameters were within the range of values determined from conventional mass-balance and meteorological observations. We describe a framework for selecting appropriate weather stations and mass-balance models to represent glacier variations of large regions. There is potential for extending these calibrated mass-balance models forwards or backwards in time to construct mass-balance time series outside of the GRACE measurement window.

In spring during 2004–07 we conducted ground-penetrating radar (GPR) measurements on the Austfonna ice cap, Svalbard, with the original aim of mapping the thickness and distribution of winter snow. Here, we further exploit the information content of the data and derive a multi-year sequence of glacier-facies distribution that provides valuable spatial information about the total surface mass balance (SMB) of the ice cap, beyond the usually evaluated winter balance. We find that following an initial decrease in the extent of the firn area (2003–04), the firn line lowered within two subsequent years by ∼40–100m elevation in the north and west and 150–230m in the south and east of the ice cap, corresponding to a lateral expansion of the firn area along the profiles by up to 7.3 and 13.3 km, respectively. The growth of the firn area is in line with stake measurements from Etonbreen that indicate a trend towards less negative SMB over the corresponding period.

Benchmark glaciers were established in many alpine areas during the 1960s as part of the International Hydrological Decade to represent ‘typical’ mass and energy processes on glaciers in different climatic regions around the world. These glaciers have received new interest in the past decade because they are used to infer the contribution of alpine glacier wastage to global sea-level rise. We compare South Cascade Glacier, the benchmark glacier for the northwest contiguous USA, and four other secondary glaciers, against the topographic, area and mass changes of 321 glaciers in the surrounding region. Results show that South Cascade Glacier is unusually large, of lower slope and much larger area and had mass losses greater than most other glaciers in the region. Three of the four secondary glaciers were much more typical. Year-to-year variations in mass balance were highly correlated between all five glaciers, and any of these glaciers, including the benchmark glacier, could be used to infer temporal mass variations in the region. However, the use of South Cascade Glacier to estimate area/mass losses for the region would result in overestimating the area/mass changes by a factor of three. Local differences in the magnitude of annual glacier mass balance control cumulative mass changes and area changes. There appears to be no way to select a representative glacier a priori, and knowledge of changes over the region is required. Therefore, there may be great uncertainty in estimates of sea-level rise from the wastage of alpine glaciers based on the benchmark approach. We recommend re-evaluation of regional glacier mass changes inferred from benchmark glaciers in critical regions.

The direct comparison of modeled glacier mass-balance distribution with field measurements could be problematic, as the methodology of determination and the processes considered at the point or catchment scale could differ strongly. Moreover, direct measurements cover only small parts of a glacier, and model performance is thus difficult to assess outside these regions. Remaining opportunities for model validation include comparison of snowlines, as derived from remote-sensing data, and maps of the mass-balance distribution, as interpreted by observers with local knowledge. This study compares such hand-drawn maps of the Vernagtferner (Oetzal Alps) mass balance with the modeled pattern as obtained from a distributed energy-/mass-balance model of intermediate complexity. The model is driven by measured daily values of temperature, global radiation and precipitation from a nearby climate station and grids of mean daily potential global radiation and climatologic annual precipitation sums. Compared with the direct measurements, the calculated mean mass balance and equilibrium-line altitude agreed very well in both balance years, although the spatial pattern of the mass-balance distribution displayed larger deviations in regions influenced by snowdrift or local topographic undulations. However, compared with the remaining snow as visible on a satellite image from 1999, the modeled snowline pattern for a larger sample of glaciers is in very good agreement.

Mass loss from the Greenland ice sheet over the past decade has caused the impression that the ice sheet has been behaving anomalously to the warming of the 1990s. We have reconstructed the recent (1866–2005) surface mass-balance (SMB) history of the Greenland ice sheet on a 5 × 5 km grid using a runoff-retention model based on the positive degree-day method. The model is forced with new datasets of temperature and precipitation patterns dating back to 1866.We use an innovative method to account for the influence of year-on-year surface elevation changes on SMB estimates and have found this effect to be minor. All SMB estimates are made relative to the 1961–90 average SMB and we compare annual SMB estimates from the period 1995–2005 to a similar period in the past (1923–33) where SMB was comparable, and conclude that the present-day changes are not exceptional within the last 140 years. Peripheral thinning has dominated the SMB response during the past decade, as in 1923–33, but we also show that thinning was not restricted to the margins during this earlier period.

For estimation of the mass balance of an unmeasured glacier, its area distribution with altitude, s (h), generally is the only available quantitative information. The appropriate specific balance profile, b (h), needs to be transferred from a measured glacier, where transfer means modification and adaptation to the topographic and climatic situation of the unmeasured glacier, such as altitude, exposure to sun and wind, or temperature. This study proposes the area median elevation, M, as a parameter of prime importance for the transfer. Using as an example ten Alpine glaciers, the similarity of M and equilibrium-line altitude is quantified and the effect of aspect and surrounding topography is qualitatively suggested. The transfer of b (h) between well-measured glaciers yielded differences in the mean specific balance of 150 mm in the mean of a 10 year period, which corresponds to a change in median altitude by 30 m. Transfer of b (h) with a shift according to median glacier elevation to a basin with 27 glaciers and 23 km2 ice cover agreed to within 10% with elevation changes converted from digital elevation models of 1969 and 1997.

This paper reviews data on glacier mass balance together with extra metadata on topography and climate to put the data into context. The 2007 Intergovernmental Panel on Climate Change (IPCC) estimates of global average glacier mass balance may not be much different from simple averages. A more mathematically correct approach is to analyse long and continuous mass-balance series measured in different regions, but there are few long series and they do not cover the globe in any representative way. However, 30 year series from 30 glaciers confirm a recent (1996–2005) trend to very negative mass balance after two decades of nearly zero mass balance. Climate data from a global gridded climatology are applied to datasets for global glacier cover, for 318 glaciers with mass-balance data for at least 1 year and for 30 glaciers with 30 year series of measurements. Results show that mean precipitation is relatively low in the global glacier-cover dataset and much higher for the observed glaciers. This shows that current mass-balance measurements are biased towards wetter conditions than are typical for global glacier cover. We urgently need to find better ways of analysing sparse datasets with ‘complex spatial and temporal patterns’ like the present mass-balance dataset.

The re-analysis of long-term mass-balance time series is important to provide bias-corrected mass-balance data for climate-change impact studies. A method to homogenize time series of comprehensive mass-balance monitoring programmes is presented and applied to the nearly 50 year mass-balance records of Griesgletscher and Silvrettagletscher, Switzerland. Using a distributed mass-balance model in daily resolution we correct the mass-balance data for varying observation dates. Direct point measurements are combined with independent geodetic mass changes, a prerequisite for a thorough homogenization of mass-balance records. Differences between mass balance evaluated in the hydrological year or according to the measurement period and the stratigraphic system are analysed and may be up to ±0.5mw.e. a−1. Cumulative mass balance of both glaciers based on the glaciological method generally agrees well with geodetic mass change on the investigated glaciers. However, for Silvretta-gletscher a significant bias of +0.37mw.e. a−1 has been detected and corrected for since 1994.

Four long-term time series of seasonal mass-balance observations, all starting in 1914, have been compiled for two stakes on Claridenfirn and one stake on Grosser Aletschgletscher and Silvrettagletscher, Switzerland. These data represent the longest records of mass balance worldwide. A mass-balance model based on the temperature-index approach is used to correct field data for varying observation dates and data gaps and to separate accumulation and ablation. The homogenized continuous 93 year time series cover most of the 20th century and enable us to investigate temporal, regional and altitudinal variability in mass balance and changes in the climatic forcing on glaciers. A high-altitude site shows summer balance trends opposite to those at three stakes located near the equilibrium line. Since 1975, melt rates have increased by 10%(10 a)−1 periods of enhanced climatic forcing are detected: 1943–53 and 1987–2007. The energy consumed for melt was higher in the 1940s despite lower air temperatures compared to the years since 1987. We find evidence for a change in the glacier surface heat budget, which has important implications for the long-term stability of degree-day factors in empirical temperature-index modelling.

A simple model uses daily observations of precipitation and temperature at a nearby weather station to estimate glacier-average seasonal mass-balance components at South Cascade Glacier, Washington, USA, from 1935, 24 years before measurements began at the glacier. This is 13 years earlier than measurements that can be derived using the NCEP–NCAR reanalysis database (begins 1 January 1948). Although the model’s error in estimating winter balance and summer balance over 1959–2006 is greater than that of a model using the reanalysis database, its error in estimating net balance is comparable. The model uses an empirically determined precipitation ratio between the station and the glacier, and a seasonally varying temperature lapse rate determined from 9 years of measurements at the glacier. Temperature is used with a degree-day formulation to estimate ablation and to partition precipitation between rain and snow for estimating accumulation. Both processes are assumed to exist throughout the year, and model results are compared seasonally with adjusted observations of winter and summer balances. The published mass-balance series is adjusted to a constant-topography (1970) series in an attempt to remove the influence of changing topography on the glacier’s response to climate. The reconstructed values prior to 1959 are also with respect to the 1970 glacier topography. Because precipitation is measured at the weather station, rather than being inferred from other meteorological variables, it enables us to distinguish more accurately between wet-day and dry-day conditions, including vertical lapse rates of temperature.