We present an update of the ‘key points’ from the Antarctic Climate Change and the Environment (ACCE) report that was published by the Scientific Committee on Antarctic Research (SCAR) in 2009. We summarise subsequent advances in knowledge concerning how the climates of the Antarctic and Southern Ocean have changed in the past, how they might change in the future, and examine the associated impacts on the marine and terrestrial biota. We also incorporate relevant material presented by SCAR to the Antarctic Treaty Consultative Meetings, and make use of emerging results that will form part of the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report.

'Ice-sheet mass balance and climate change. ', Nature., 498 (7452). pp. 51-59. Further information on publisher's website:http://dx.doi.org/10.1038/nature12238Publisher's copyright statement:Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Greenland is losing mass at an increasing pace, Antarctic loss is likely to be less than some 52 recently-published estimates. It remains unclear whether East Antarctica has been gaining 53 or losing mass over the last twenty years, and uncertainties in mass change for West 54Antarctica and the Antarctic Peninsula remain large. We highlight the last six years of 55 progress and examine the key problems that remain. (primarily snow accumulation) and mass losses (primarily melt-water runoff and solid ice 74 dynamical discharge across the grounding line). Surface mass balance (SMB) is the net 75 balance of mass gains and losses at the ice-sheet surface and does not include dynamical 76 mass loss. Efforts to determine ice-sheet mass balance using the three satellite geodetic 77 techniques of altimetry, interferometry, and gravimetry (see Section 2.1) have recently 78 been sharpened by carefully defining common spatial and temporal domains for inter-79 comparison 2 . Here we review the latest mass balance estimates for the Antarctic (AIS) and 80Greenland (GrIS) ice sheets. New glacial isostatic adjustment (GIA) models, tested and 81 evaluated against Global Positioning System (GPS) data, have recently led to significant 82 downwards revision in GIA, and hence downwards revisions of gravimetric and altimetric 83 satellite estimates of Antarctic mass loss 2 (Box 1). 84Since IPCC AR4, ice-sheet models are no longer constrained to using overly 85 simplified physics, allowing them to more accurately simulate the important coupling 86 between ice sheets, ice streams and ice shelves. This major advance has been accompanied 87 by improved model representation of the complex interactions of the ice-sheet with its bed, 88 the atmosphere and the ocean. For completeness we also discuss briefly the contributions 89 to sea-level rise (SLR) from other sources, namely glaciers and ice caps, thermal expansion 90 of the oceans and terrestrial water storage changes. Similarly, GRACE and radar and laser altimetry studies require the effects of GIA-121 related vertical bedrock motion (Box 1) to be accurately removed. Such vertical motion 122 could be misinterpreted as ice-mass change by the GRACE satellites or ice-thickness change 123 by radar and laser altimeters, and a GIA correction m...

The Antarctic Peninsula (AP) is often described as a region with one of the largest warming trends on Earth since the 1950s, based on the temperature trend of 0.54°C/decade during 1951-2011 recorded at Faraday/Vernadsky station. Accordingly, most works describing the evolution of the natural systems in the AP region cite this extreme trend as the underlying cause of their observed changes. However, a recent analysis (Turner et al., 2016) has shown that the regionally stacked temperature record for the last three decades has shifted from a warming trend of 0.32°C/decade during 1979-1997 to a cooling trend of -0.47°C/decade during 1999-2014. While that study focuses on the period 1979-2014, averaging the data over the entire AP region, we here update and re-assess the spatially-distributed temperature trends and inter-decadal variability from 1950 to 2015, using data from ten stations distributed across the AP region. We show that Faraday/Vernadsky warming trend is an extreme case, circa twice those of the long-term records from other parts of the northern AP. Our results also indicate that the cooling initiated in 1998/1999 has been most significant in the N and NE of the AP and the South Shetland Islands (>0.5°C between the two last decades), modest in the Orkney Islands, and absent in the SW of the AP. This recent cooling has already impacted the cryosphere in the northern AP, including slow-down of glacier recession, a shift to surface mass gains of the peripheral glacier and a thinning of the active layer of permafrost in northern AP islands.

Red-snow algae are red-pigmented unicellular algae that appear seasonally on the surface of thawing snow worldwide. Here, we analyse the distribution patterns of snow algae sampled from glaciers and snow patches in the Arctic and Antarctica based on nuclear ITS2 sequences, which evolve rapidly. The number of phylotypes is limited in both polar regions, and most are specific to either the Arctic or Antarctica. However, the bipolar phylotypes account for the largest share (37.3%) of all sequences, suggesting that red-algal blooms in polar regions may comprise mainly cosmopolitan phylotypes but also include endemic organisms, which are distributed either in the Arctic or Antarctica.

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[1] Radar layer geometry in divide areas is strongly influenced by the operation of the Raymond effect, which causes upwarping of the layers as a consequence of the nonlinear rheology of ice. The detailed geometry of these layers is known to store a record of change in the cryosphere, of local thinning, and of the age of formation of the divide and has been surmised to provide information about lateral motion of divides. Such lateral motion can be caused by changes in flanking ice streams, and the divide area thereby contains a record of ice stream dynamics. It has also been suggested that a large perturbation of divide position will obliterate the cumulative effects of the operation of the Raymond mechanism, leading to the disappearance of Raymond bumps. Since the Raymond effect has a strong influence on the age-depth relation in ice cores, knowledge of whether its operation is localized (leading to strong bump formation) or distributed is crucial in the interpretation of ice cores. The detailed evolution of ice divide radar layer geometry remains poorly understood. Employing a full thermomechanically coupled transient model, we qualitatively explore the effect of divide migration on radar layer geometry. Certain qualitative features emerge which can be used to infer history of cryosphere change, in particular, in areas distant from the usual sites of geological dating. There remains uncertainty about the influence of sliding on the operation of the Raymond effect. Under certain conditions, the existence of sliding can damp or eliminate the operation of the Raymond effect. If this is generally true, then dating of ice divides may simply be a date for the freezing of the divide bottom. We show that sliding does not necessarily eliminate the formation of bumps. Dates of divide formation are likely to be dates for the location of the ridge at a particular spot. Raymond bump evolution is weakened by flow along the ridge. We explore quantitatively the strength of this effect, using a scaling analysis to show that the weakening can efficiently be described by one parameter, the ratio of along-ridge slope to a measure of the across-divide curvature.Citation: Martín, C., R. C. A. Hindmarsh, and F. J. Navarro (2009), On the effects of divide migration, along-ridge flow, and basal sliding on isochrones near an ice divide,

Calving from tidewater glaciers and ice shelves accounts for around half the mass loss from both polar ice sheets, yet the process is not well represented in prognostic models of ice dynamics. Benn and others proposed a calving criterion appropriate for both grounded and floating glacier tongues or ice shelves, based on the penetration depth of transverse crevasses near the calving front, computed using Nye's formula. The criterion is readily incorporated into glacier and ice-sheet models, but has not been fully validated with observations. We apply a three-dimensional extension of Benn and others' criterion, incorporated into a full-Stokes model of glacier dynamics, to estimate the current position of the calving front of Johnsons Glacier, Antarctica. We find that two improvements to the original model are necessary to accurately reproduce the observed calving front: (1) computation of the tensile deviatoric stress opening the crevasse using the full-stress solution and (2) consideration of such a tensile stress as a function of depth. Our modelling results also suggest that Johnsons Glacier has a polythermal structure, rather than the temperate structure suggested by earlier studies.

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