Editor's choice 

The history and extent of the Greenland ice sheet is a widely debated and poorly understood question. In this study, the authors show that the childhood of the Greenland ice sheet took place in the southern and eastern highlands of Greenland, and further suggest that the continental ice sheet we observe today first emerged between 7 million years and 2.6 million years ago.

This study addresses an important question regarding the stability of ice shelves, a question that is highly relevant for Greenland and Antarctica. Using a unique combination of observations, the authors document extensive thinning and extremely high basal melt rates at the floating tongue Nioghalvfjerdsbræ, North Greenland, an important and fast-changing part of the Greenland Ice Sheet. The increase in melt rates are suggested to be caused by an increase in surface melt that is funneling surface water under the ice shelf.

This study provides new estimates of historical and projected changes in pan-Arctic runoff, with emphasis on the impact of permafrost changes and sub-surface flows on large scale hydrology. The impact of permafrost change on hydrological processes is a key uncertainty facing the cold regions hydrology community, and requires comprehensive model-based analysis as presented in this study. The analysis also addresses changes to the terrestrial runoff contribution to the freshwater budget of the Arctic, and so is of interest to a wide range of disciplines.

The ongoing acceleration and disintegration of Antarctic ice shelves is a topic of keen interest to the scientific community. Recent years have seen multiple calving events, some of which have produced large icebergs. In this study, the effect of such a large iceberg-calving event is studied through remote sensing data. The authors show how the break-off of the iceberg led to significant ice speed-up, demonstrating the important effect of calving on the ice shelves.

This research is part of an exciting advancement in the field of glaciology, driven by machine learning. The study focuses on crevasse detection, a highly relevant topic from a scientific and logistic perspective. Crevasses may aid surface meltwater to penetrate through the ice thus impacting ice dynamics. Crevasses also pose a logistical challenge for fieldwork in the polar regions. In this study, the authors are able to automatically spot grounded crevasses using a Convolutional Neural Networks algorithm. One of the focus areas is the Thwaites Glacier, an area that has recently been subject to extensive scientific research due to its importance for the stability of the West Antarctic Ice Sheet.

This paper is worthy of a highlight. The authors show the importance of a process that has been known to exist but hasn’t been measured in this detail before. From a public interest perspective, the results might be tricky to explain in general terms, but the key results fit within the category of “major discovery” and/or “mystery”.

This study demonstrates the connection between two important parts of the climate system: atmospheric conditions over the Greenland Ice Sheet and the seasonal ice flow of glaciers -- specifically a glacier in Southwest Greenland. The authors use GPS measurements to identify more than 40 cases of speed up of the glacier. The majority of the observed speed up can be linked to the melting of the surface of the ice. In particular, the study shows that atmospheric rivers are linked to the strongest speed-up events. The findings have implications for the future dynamics of Greenlandic glaciers as weather patterns change intensity in response to the warming climate.

This study is worthy of a highlight. The new indicator (Glacier Loss Day) is accessible to the non-expert, and may capture public interest (the authors compare Glacier Loss Day to Earth Overshoot Day, which is a fair comparison). Given the dramatic summer mass loss of glaciers in the Alps in recent years, this work has high potential to generate media interest.

Oldest Ice is a large project with broad interest and appealing targets. This study shows (i) that the current Beyond EPICA and Million Year Ice Core drilling projects at Little Dome C in Antarctica are expected to extract continuous ice core of almost 1.5 million years; and (ii) estimates the spatial extent of a stagnant ice layer in the Dome C region. This layer of ice could be millions of years old and could have large scale implications for the whole Antarctic ice sheet dynamics.

This paper presents changes in thickness, flow and basal melt of Antarctic ice shelves over the past 26 years at relatively high resolution. An analysis based on an ocean model investigates the ice-ocean feedbacks. Overall, this is very useful for a large Antarctic research community.

This manuscript describes a very unique set of measurements made in extreme conditions at the summit of Mount Everest. This accomplishment provides a new perspective on snow conditions at an iconic location, and will be of broad public interest.

This paper describes a very dramatic rate of landscape change that is both scientifically notable across the geoscience community, and of general interest to the public. The key messages can be communicated in a very accessible way, and the satellite imagery associated with the analysis clearly show the high impact changes to the valley.

In recent years there has been growing concern about the potentially irreversible retreat of the West Antarctic Ice Sheet and Thwaites Glacier in particular causing deglaciation of large parts of the ice sheet and leading to substantial sea-level rise. This study demonstrates that a site between Thwaites and Pope glaciers has undergone ice-sheet thinning and subsequent thickening in the past. The results are of importance for a better understanding of future threats to the stability of the West Antarctic ice sheet, and the ice-sheet evolution in the Amundsen sector over the late Holocene.

Atmospheric rivers are short-lived events that can have important impacts on the ice sheets but are not well resolved in climate models. They give rise to ice shelf loss and widespread melt in some areas but ice gain in others. The region of interest of this paper, Thwaites Glacier in West Antarctica, is one of the most important to understand in detail given potential sea level rise impacts and this study is therefore of interest to stakeholders and the general public as well as scientists concerned with atmosphere ice sheet interactions. The paper also sheds light on synoptic situations that lead to ARs and it is therefore of broad general scientific interest.

The study shows a rare example of the thickening of a glacier ice tongue in East Antarctica. The authors attribute the thickening to changes in wind patterns leading to a decrease in the transport of warm water reaching the glacier. The results highlight the intricate relationship between glaciers and atmosphere/ocean dynamics.

This manuscript addresses an urgent problem: the proper quantification and attribution of uncertainties relating to sea-level rise. The authors show how a machine-learning approach may show the way towards a more rigorous treatment of these uncertainties, and how this might be used for policy making.

This study draws attention to some important processes for ice sheet mass loss. In particular, the warm-water incursions onto the large ice shelves in the late 21st century, inducing more melt, have big implications for the future contribution to SLR from Antarctica.

This paper shows that the changes observed in the North of the Greenland ice sheet mainly result from Arctic sea ice decline and are less dependent on the atmospheric circulation variability in North-Atlantic sector. The sea ice decline, therefore, exerts another (indirect) anthropogenic-driven influence on mass loss in Greenland.

Goliber et al. present a rich new dataset for the lengths of 278 glaciers around Greenland. This dataset, "TermPicks", contains 39,060 detailed traces of the edges of these glaciers, where ice meets ocean. TermPicks spans the entire satellite record (1970s-present), with air photo coverage for some glaciers going back >100 years to 1916. TermPicks is designed for use as training data in machine learning applications, which are the future of the tedious "terminus picking" work that has largely been performed by students to date. Thus, TermPicks will facilitate a significant leap forward in Greenland glacier research by facilitating machine-learning-enabled analysis of the continual high-flux, big-data output of high-resolution imagery by our international constellation of earth-observing satellites.

This paper provides a complete and novel perspective on how to attribute changes in glaciers to anthropogenic warming. It is accessible, well written with clear figures, and will certainly be of interest to the wider community.

Justification of handling editor: The paper presents a multi-proxy study of fjord productivity in Greenland. The link between paleo records and modern climate is notable.