Global Glacier Retreat Research Articles

Modelling regional glacier length changes over the last millennium using the Open Global Glacier Model

Abstract. A large majority of the direct observational record for glacier changes falls within the industrial period, from the 19th century onward, associated with global glacier retreat. Given this availability of data and the significant focus in contemporary glacier modelling falling on recent retreat, glacier models are typically calibrated using – and validated with – only observations of glaciers that are considerably out of equilibrium. In order to develop a broader picture of the skill of one glacier model – the Open Global Glacier Model (OGGM) – we model glaciers for extended historical timescales of 850–2004 CE using a selection of six general circulation model (GCM) outputs. We select glaciers for which long-term length observations are available in order to compare these observations with the model results, and we find glaciers with such observations in almost all glacierised regions globally. In many regions, the mean modelled glacier changes are consistent with observations, with recent observed retreat in these regions typically at the steeper end of the range of modelled retreats. However, on the scale of individual glaciers, performance of the model is worse, with overall correlation between observed and modelled retreat weak for all of the GCM datasets used to force the model. We also model the same set of glaciers using modified climate time series from each of the six GCMs that keep temperature or precipitation constant, testing the impact of each individually. Temperature typically explains considerably more variance in glacier lengths than precipitation, but results suggest that the interaction between the two is also significant within OGGM and neither can be seen as a simple proxy for glacier length changes. OGGM proves capable of reproducing recent observational trends on at least a qualitative level in many regions, with a modelling period over a considerably larger timescale than it is calibrated for. Prospects are good for more widespread use of OGGM for timescales extending to the pre-industrial period, where glaciers were typically larger and experience less rapid (and less globally consistent) geometry changes, but additional calibration will be required in order to have confidence in the magnitude of modelled changes, particularly on the scale of individual glaciers.

Identification of local water resource vulnerability to rapid deglaciation in Alberta

Global glacier retreat driven by climate change will have major impacts on regional water availability, as many communities rely on glacier runoff for water supply during warm and dry seasons. A community whose water resources are potentially vulnerable is one that sources water from a glacier-fed river where that river is expected to substantially change if glacier contributions become negligible. However, regional assessments identifying which communities’ water resources are most vulnerable to such changes are lacking. Here we use observed streamflow measurements, gridded climate data and a database of municipal water sources for communities in Alberta, Canada, to identify the relative importance of glacier runoff at the local scale. In a scenario of negligible glacier runoff, we predict unprecedented streamflow lows at several communities. This approach provides a methodology to identify communities whose water resources may be vulnerable to glacier retreat and would benefit from more-focused research. Climate warming over Canada drives glacier retreat and threatens water resources in regions that rely on downstream meltwater. Streamflow and climate data are combined with a municipal water source database to identify Alberta communities whose water supply would be most impacted by glacier retreat.

Regional differences in global glacier retreat from 1980 to 2015

Global warming triggers shrinking and thinning of glaciers worldwide, with potentially severe implications for human society. However, regional differences in glacier retreat and its relationship with climatic characteristics have not been conclusively demonstrated. In this study, regional changes in global glaciers based on two primary features, area change and mass balance, were investigated on the basis of data collected from published research on glacier changes. Results show that during the period 1980–2015, the rate of global glacier area shrinkage was 0.18% per year and that of global glacier mass loss was 0.25 m w.e. per year. Retreat of glaciers located at low and middle latitudes was characterized by severe area shrinkage and mass loss. Correspondingly, in the Arctic, deglaciation was characterized by ice thinning due to a low area reduction but relatively high mass loss rate. However, glaciers in high southern latitudes were in a relatively stable status. High Mountain Asia exhibited the lowest rate of area shrinkage and mass loss among glaciers located at low and middle latitudes, and a slower rate of mass loss compared with the global average. Glaciers in the Tropical Andes exhibited the fastest rate of glacier area shrinkage (−1.6% per year), whereas Antarctic and Subantarctic glaciers showed the lowest rate (−0.11% per year). For mass balance, the most negative occurred at Southern Andes (−0.81 m w.e. per year), followed by Alaska (−0.74 m w.e. per year). Only the Antarctic and Subantarctic experienced small mass gain (0.04 m w.e. per year). High levels of correlation are found between the rates of glacier retreat and annual average temperature and annual total precipitation instead of their trends. The variability of the surface climate conditions in the glacier environment plays a key role in driving these regional differences in global glacier retreat.

Glacier fluctuations during the past 2000 years

Abstract A global compilation of glacier advances and retreats for the past two millennia grouped by 17 regions (excluding Antarctica) highlights the nature of glacier fluctuations during the late Holocene. The dataset includes 275 time series of glacier fluctuations based on historical, tree ring, lake sediment, radiocarbon and terrestrial cosmogenic nuclide data. The most detailed and reliable series for individual glaciers and regional compilations are compared with summer temperature and, when available, winter precipitation reconstructions, the most important parameters for glacier mass balance. In many cases major glacier advances correlate with multi-decadal periods of decreased summer temperature. In a few cases, such as in Arctic Alaska and western Canada, some glacier advances occurred during relatively warm wet times. The timing and scale of glacier fluctuations over the past two millennia varies greatly from region to region. However, the number of glacier advances shows a clear pattern for the high, mid and low latitudes and, hence, points to common forcing factors acting at the global scale. Globally, during the first millennium CE glaciers were smaller than between the advances in 13th to early 20th centuries CE. The precise extent of glacier retreat in the first millennium is not well defined; however, the most conservative estimates indicate that during the 1st and 2nd centuries in some regions glaciers were smaller than at the end of 20th/early 21st centuries. Other periods of glacier retreat are identified regionally during the 5th and 8th centuries in the European Alps, in the 3rd–6th and 9th centuries in Norway, during the 10th–13th centuries in southern Alaska, and in the 18th century in Spitsbergen. However, no single period of common global glacier retreat of centennial duration, except for the past century, has yet been identified. In contrast, the view that the Little Ice Age was a period of global glacier expansion beginning in the 13th century (or earlier) and reaching a maximum in 17th–19th centuries is supported by our data. The pattern of glacier variations in the past two millennia corresponds with cooling in reconstructed temperature records at the continental and hemispheric scales. The number of glacier advances also broadly matches periods showing high volcanic activity and low solar irradiance over the past two millennia, although the resolution of most glacier chronologies is not enough for robust statistical correlations. Glacier retreat in the past 100–150 years corresponds to the anthropogenic global temperature increase. Many questions concerning the relative strength of forcing factors that drove glacier variations in the past 2 ka still remain.

Glaciers. Attribution of global glacier mass loss to anthropogenic and natural causes.

The ongoing global glacier retreat is affecting human societies by causing sea-level rise, changing seasonal water availability, and increasing geohazards. Melting glaciers are an icon of anthropogenic climate change. However, glacier response times are typically decades or longer, which implies that the present-day glacier retreat is a mixed response to past and current natural climate variability and current anthropogenic forcing. Here we show that only 25 ± 35% of the global glacier mass loss during the period from 1851 to 2010 is attributable to anthropogenic causes. Nevertheless, the anthropogenic signal is detectable with high confidence in glacier mass balance observations during 1991 to 2010, and the anthropogenic fraction of global glacier mass loss during that period has increased to 69 ± 24%.