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Glaciers will lose mass during the next decades as the climate warms. While the largest uncertainty in this mass loss is the global greenhouse gas emissions pathway, on a local or regional scale there are large uncertainties in some processes that influence glacier response. We explore the competing processes of reduced ablation under debris cover and increased ablation from calving by applying a coupled mass-balance/ice-flow model in the central Southern Alps/Kā Tiritiri o te Moana of New Zealand. Glacier volume loss is assessed over the period from AD 1880 to AD 2099, driven by observed climate data before 2005, and perturbing the modern climate state and imposing representative concentration pathway (RCP) scenarios 2.6–8.5 as expressed by six global circulation models (GCMs) which leads to a regional warming of between 1–4 °C (2006–2099). Key findings are (1) modelled ice volume reduced from 47 km3 to 29 km3 between AD 1880 and 2005; (2) over the period 2006–2099 further volume loss to 24 km3 (19% reduction) is committed under present-day climate; (3) modelled ice volume at AD 2099 is estimated at 2 km3 ± 6 km3 (RCP8.5) to 15 km3 ± 6 km3 (RCP2.6), a reduction of 50–92% relative to present day. The wide range of projected ice volumes reflects the large range of temperature projections between RCP2.6 and RCP8.5. The mode and timing of ice loss provides insight into processes that will drive future glacier behavior. Under RCP2.6 at 2099, the glaciers retain a similar configuration to present, although clean-ice glaciers will retreat significantly, and some debris-covered tongues will disconnect from their accumulation areas. For RCP4.5, RCP6.0 and RCP8.5 the clean-ice glaciers will retreat to become small remnants in the high mountains. Experiments where the debris cover is removed shows a much faster loss of ice, whereas experiments with no lake calving slows ice loss. However, under all but the most moderate warming scenarios, by 2099 the strong climatic forcing overwhelms these processes as there is little ice left at low elevations where debris cover and lake calving occur.

Compilation of modern and historical length change records for Franz Josef and Fox Glaciers demonstrates that these glaciers have lost ~ 3 km in length and at least 3–4 km 2 in area since the 1800s, with the greatest overall loss occurring between 1934 and 1983. Within this dramatic and ongoing retreat, both glaciers have experienced periods of re-advance. The record from Franz Josef Glacier is the most detailed, and shows major advances from 1946 to 1951 (340 m), 1965–1967 (400 m), 1983–1999 (1420 m) and 2004–2008 (280 m). At Fox Glacier the record is similar, with advances recorded during 1964–1968 (60 m), 1985–1999 (710 m) and 2004–2008 (290 m). Apart from the latest advance event, the magnitude of advance has been greater at Franz Josef Glacier, suggesting a higher length sensitivity. Analysis of the relationship between glacier length and a reconstructed annual equilibrium line altitude (ELA) record shows that the glaciers react very quickly to ELA variations — with the greatest correlation at 3–4 years' lag. The present (2014) retreat is the fastest retreat in the records of both glaciers. While decadal length fluctuations have been linked to hemispheric ocean–atmosphere variability, the overall reduction in length is a clear sign of twentieth century warming. However, documenting glacier length changes can be challenging; especially when increased surface debris-cover makes identification of the ‘true’ terminus a convoluted process.

Mid-latitude maritime glaciers are responding quickly and directly to climate change. This response is expected to continue, and will result in maritime glaciers making a large contribution to sea level rise over the coming decades. Maritime glaciers in the New Zealand Southern Alps provide an opportunity to learn more about climate–glacier mass balance relationships in a high precipitation setting, and how these relationships might change in the future. Ice core and direct glaciological measurements are used to construct a 24-year record of net accumulation, the longest of its type in New Zealand. We demonstrate that variations in net accumulation on Tasman Glacier are more strongly influenced by temperature than by precipitation. Further, it is temperature during the ablation season that exerts most control. Atmospheric circulation patterns, in particular the state of the El Nino Southern Oscillation (ENSO) and Southern Annular Mode (SAM), were found to influence net accumulation. When the SAM is positive and the ENSO in a La Nina phase, easterly and northerly wind anomalies are enhanced, temperatures increase in the Southern Alps region and more negative glacier mass balances result. Conversely when SAM is negative and ENSO in an El Nino phase, westerly and southerly wind anomalies occur, and temperatures decrease in the Southern Alps region. In this case, glacier mass balance is more likely to be positive. However, relationships between glacier mass balance and these atmospheric circulation modes are not simply linear, with some of the lowest net accumulation years associated with inverse polarity between the SAM and the ENSO.

Understanding the response of relatively small ice masses to climate change on a century-to-century timescale is important because of their significant contribution to sea level change in the recent past, and their likely contribution in the next century. Franz Josef Glacier, with its excellent terminus position record, location in the Southern Hemisphere, and its extreme sensitivity to climatic changes, is a key data point for understanding the magnitude and mechanisms of past and future climate changes. Here, we use a reconstructed mass balance record to drive an ice flow model which simulates the general retreat of the glacier during the 20th century. The model is then used to project future glacier variations, based on regionally downscaled climate change scenarios. The results indicate that, under a mean climate change scenario, the glacier will retreat 5 km and lose 38% of its mass by 2100. Different scenarios give a range of recession from 3.9 to 6.4 km, and a range of volume loss from 26% to 58%. On a global scale, the magnitude of the retreat is at the upper end of the range calculated for other, similar sized, glaciers.

The late Holocene retreat of the West Antarctic ice sheet is crucial information for assessing its current dynamics. However, data from this period for parts of the ice sheet where significant change has taken place, mainly the Ross Sea, are very sparse. Some significant dated deposits are from lakes dammed by valley glaciers, themselves dammed by the Ross Ice Sheet. The least age of these deposits is somewhat later than the retreat of the Ross Ice Sheet from the locality on account of the lagged response of the glacier. We present a model of the Hatherton Glacier, which examines its relationship to the Ross ice sheet, using dated margin data from ice-dammed lakes. Problems in modelling are the coupling with the Darwin Glacier, the unknown bed topography and the poorly known surface mass balance, which include blue ice areas. We infer the bed topography by tuning a valley glacier model, and use this model to (i) estimate the thickness of the Last Glacial Maximum (LGM) Ross Ice Sheet; and (ii) estimate the response time of the Hatherton Glacier to changes in the Ross Sea ice sheet. The best fit of the glacier surface profile to the geological data occur if the LGM Ross Ice Sheet elevation is assumed to be 800 m higher than the present-day ice shelf surface. If the decay of the Ross Ice sheet is linear with time, the response time is of the order of several centuries. Step changes in the elevation of the Ross Ice Sheet lead to a response time around one thousand years. The dated deposits in the Hatherton Valley cannot be used directly as dates of Ross Ice Sheet grounding line retreat.