Main SESSIONS

The Greenland ice sheet is the largest ice mass in the Northern Hemisphere, playing an important role in the Arctic climate system. If all the ice in Greenland melted, global sea level would rise by 7 m. Glaciation was initiated in Greenland more than 10 million years ago but evidence from deep ice cores and radio echo-sounding indicates that the continuous age-sequence of layers in the current ice sheet only reaches into the Eemian interglacial (~130,000 years BP). Significant warming has been detected over the ice sheet during the last 30 years, leading to increasing duration and intensity of melt-events. During recent years, the Greenland ice sheet has probably been the single largest contributor to ongoing global sea-level rise from land sources. Modelling studies suggest that meltwater delivery from the ice sheet may raise sea-level by up to 0.3 m during this century. Recent studies have focused on constraining the relative contributions of surface mass balance and dynamic thinning of outlet glaciers to the total mass loss. Intensive research is also being carried out on the response of the subglacial hydrological system in South Greenland to increased surface melting, on the dynamics of fast-flowing ice streams like the Jakobshavn Isbræ and on the stability of the North-East Greenland Ice Stream in a warmer climate. Presentations in this session can cover, but are not limited to, the following topics:

• Greenland ice sheet history
• Paleoclimate from ice cores
• Internal structure
• Recent changes
• Likely response to future warming
• Contribution of Greenland mass loss to sea level rise
• Research on surface melt lakes and runoff
• Ice velocity studies

Sea ice covers on average 24 million km2 of Earth's polar oceans, but its extent varies greatly with the seasons in both hemispheres, affected by winds, currents, and fluxes of heat and radiation. In the North, the Arctic Ocean is contained by the coasts of Greenland, Canada, Alaska, and Siberia. In the South, sea ice can expand freely into the Southern Ocean around the Antarctic continent in winter. Sea ice is a key component of the climate system, influencing surface heat, evaporation, radiation, and freshwater fluxes. Since the start of satellite monitoring in 1979, the mid-winter sea-ice cover in the Arctic has declined by 3% per decade, and the minimum extent at the end of summer by 13% per decade. No trend has been observed in the area of sea ice around Antarctica during the satellite era, but record summer lows were recorded in 2017 and 2018. Thickness of ice across the central Arctic Ocean declined from 3.6 m to 1.3 m between 1975 and 2012 and the extent of multi-year ice has diminished. There is little information about ice thickness changes in the Southern Ocean. The length of the Arctic melt season has increased by 10 days per decade since 1979 and a linear relationship is found between reductions in Arctic sea ice and global temperatures. Modelling results indicate that if global warming is limited to 2°C, the likelihood of an ice-free Arctic Ocean in summer will be 10–35% each year a decade after stabilization of the climate.

• Nature and distribution of sea ice
• Changes in area, thickness and volume
• Likely changes during the 21st century
• Importance of sea ice in Earth´s climate system
• Ongoing developments in the Arctic (shipping, settlements, research coverage)

Environmental conditions in areas where the cryosphere exists are generally harsh and observations there are costly. In fact, some cryospheric observing networks are declining due to lack of investment. Satellite monitoring overcomes the logistical obstacles to surface measurements, and space-based data are essential for delivering sustained, consistent observations of the global cryosphere. However, satellites are expensive, they do not fully address the range of geophysical variables needed to understand the cryosphere, and those variables that are measured often have large uncertainties. Airborne observations provide key data that cannot currently be measured from space, more detailed information in critical areas, and observations with which to calibrate and validate satellite retrievals. While the surface, aircraft, and satellite observing systems have provided invaluable data for improving our understanding of the cryosphere and its place in the global climate system, their deficiencies leave us with critical gaps. What are the current observational and research gaps and what new technologies can address them? Presentations in this session may cover the following topics as well as others that are relevant to cryospheric monitoring:

• Current observational, research, and long-term monitoring gaps;
• Networks of ground-based and ocean instrumentation;
• Observer networks for river ice, lake ice, and snow, via schools and native communities;
• Coordination of research and operational cryospheric observations;
• Transition of research-based observing systems into sustained, operational observations;
• New technologies for observing the cryosphere;
• Long-term, consistent records of cryosphere variables;
• Generation and exchange of data and information for operational services and research

Human beings in the Arctic and in high-mountain regions have successfully adapted to environments dominated by snow and ice through cultural, social and technological arrangements. However, the resilience of cryospheric cultures is now threatened by increasingly rapid environmental and social change. Coping with climatic change and other developments calls for collaboration between researchers, policy makers and local communities, to ensure inclusion of indigeneous knowledge based on historical and contemporary experience with the realities of life in cold conditions. This topic broadly addresses the interplay of social and environmental systems in cryospheric settings past, present and future.

Changes in mountain glaciers and ice caps impact local hydrological conditions, glacier-related hazards and global sea level. This session invites presentations on various physical processes occurring on glaciers and ice caps, as represented in field observations, remote sensing and modelling, in particular processes related to glacier hazards. Presentations may deal with, but are not limited to, the following topics:

• Surface energy balance;
• Surface mass fluxes;
• Glacier dynamics and evolution;
• Glacier surges and fast glacier flow;
• Conditions at the glacier bed;
• Calving mechanisms;
• Melt processes and glaciohydrology;
• Subglacial lakes;
• Risks due to outburst floods (jökulhlaups) from glaciers;
• Risks due to landslides on and adjacent to glaciers, and associated tsunamis from glacier lakes and flash floods into the proglacial terrain;
• Glaciers in high-mountain areas and impacts of their melting on populations;
• Effects of debris cover on glacier mass balance;
• Future perspectives on glacial rivers as water resources;
• Historical changes in glaciers and glacial environments;
• Ice core studies

Snow, a defining characteristic of high latitude and high-altitude regions covering land and ice surfaces, is a cross-cutting component of the cryosphere that influences surface water and energy fluxes, atmospheric dynamics and weather, biogeochemical fluxes, and ecosystem dynamics at local to global scale. On average, snow covers 46 million km2 of Earth's surface each year and is thus the largest single component of the cryosphere in terms of area. Fall- and winter-snow cover in the Northern Hemisphere has increased moderately since 1967, whereas a declining trend is observed in spring and summer. Modelling studies suggest that snow cover will decrease in area during this century, decreasing the planetary albedo and, hence, amplifying the initial warming. Ongoing improvement of our knowledge of snow processes and the temporal and spatial changes of snow-cover variables and solid precipitation is essential to meet current and future operational and policy needs, including weather and climate prediction, hydrological forecasting and climate-change detection. This session solicits overviews on such key issues, including:

• New and emerging methods and technologies related to observations and research;
• Satellite monitoring, snow trackers and derived products;
• Data integration, data archiving and exchange;
• Studies of the socio-economic impacts of changing snow conditions on runoff and water supply, especially for mountain regions and for improved hydrological forecasting in cold regions.
• Education, capacity building and international cooperation

Glaciers exist on all continents of the world at altitudes between sea level and >8000 m, in widely varying climatic settings. The total number of glaciers and ice caps outside the Greenland and Antarctic ice sheets is estimated at close to 200,000, covering approximately 700,000 km2. Satellite mapping has greatly improved estimates of the glacier cover in remote areas and estimates of the total volume of glaciers and ice caps are continually being improved. Only a few dozen long-term mass balance records from ground-based measurements on individual glaciers exist, but airborne and remote-sensing platforms are allowing estimates of ice-volume changes over glaciated regions on continental scales. Similarly, mass balance modelling is being extended from individual glaciers to entire mountain ranges. Mass loss from glaciers is occurring in all mountain regions and their projected total volume decline by the end of this century ranges between 10 and 50%, depending on scenarios. This session will highlight recent glacier changes in different parts of the world and discuss methods for constraining observational uncertainties. Presentations in this session can cover, but are not limited to, the following topics:

• Reconstructing past glacier extent and changes;
• Mass balance measurement results, using both glaciological and geodetic methods;
• Modelling future mass balance and runoff;
• Coupling of glacier mass balance models with ice flow models;
• Improving estimates of the effects of debris cover, dust deposition, internal melting, surface and firn hydrology and drifting snow on mass balance.
• Education and capacity building programmes on glacier changes worldwide

Permafrost regions cover about ¼ of the Northern Hemisphere land surface. They are mostly confined to the land areas surrounding the Arctic Ocean: Siberia, Greenland, Arctic Canada and Alaska. Frozen ground also exists in high-altitude regions around the world, on the Antarctic continent and beneath the seabed in the continental shelves of the polar regions. Landforms characteristic of permanently frozen ground include pingos, palsas, patterned ground and rock glaciers. Much of the permafrost currently in existence formed during the glacial periods of the Pleistocene, although large parts of the Earth's permafrost formed in the second part of the Holocene and during the Little Ice Age. During summer the upper part of the ground in permafrost areas is thawing to different depths – the active layer, depending on snow and vegetation cover, and subsurface conditions. Temperature profiles measured in 10–200 m deep boreholes can be used to reconstruct recent climatic variability and long-term changes in the surface-energy balance. Recent warming in Arctic and mountainous regions creates problems for infrastructure built in permafrost regions and decomposition of organic carbon in thawing soils releases carbon dioxide and methane to the atmosphere. Presentations in this session can cover, but are not limited to, the following topics:

• Nature and distribution of permafrost
• Ongoing changes in ground temperatures and active layer thickness
• Monitoring challenges
• Increased risks of landslides due to permafrost thawing
• Impacts of permafrost thaw on the hydrological cycle
• Potential release of greenhouse gases from thawing permafrost

The interactions of the cryosphere with other components of the Earth system involve the atmosphere, the oceans and the biosphere, as well as the solid Earth. Modelling of variations of the cryosphere through the ice-age cycles and other climate oscillations requires adequate representation of all these components in order to understand the rapid changes that have taken place in the past. Similarly, future climate development can only be assessed with models that represent the complex interactions and feedbacks that are activated by the anthropogenic increase of greenhouse gasses in the atmosphere. Earth system models (ESM) are designed to simulate all relevant aspects of the Earth system, including physical, chemical and biological processes. In addition to the classical climate model components (atmosphere, soil, ocean, and sea ice), Earth System models may add model representations of atmospheric chemistry and aerosols, ocean bio-geo-chemistry, dynamic vegetation, ice sheets, glaciers, permafrost and crustal deformation due to ice loading. The flow of CO2 and other greenhouse gasses through the atmosphere, biosphere, soil and the oceans, the melting of ice shelves and calving ice fronts in Antarctica and Greenland by the sea, the release of greenhouse gasses from permafrost on land and in shallow seas, and the effect of aerosols on the albedo of sea ice and snow cover are among the processes that can be analysed by Earth system models.

Presentations in this session may deal with, but are not limited to, the following topics:

• The paleoclimate of glacial and interglacial periods (including the Eem-interglacial and the rapid changes during the last glacial period), can the main characteristics of past climates be reproduced by the models?
• The cryosphere as a trigger of rapid climate change;
• Arctic amplification of future warming, simulations of Arctic sea ice and ice sheet retreat in the future.

The Antarctic ice sheet is one of the most prominent topographic features on the planet. About 60% of all freshwater on Earth is locked up in the ice sheet, holding the potential to raise global sea-level by 58 meters. Data from marine sediments yield information on the timing of initial ice sheet buildup 35 million years ago and deep ice-core records from Antarctica have provided exceptional records of climate and atmospheric history 800,000 years back in time. Fast-flowing ice streams drain the West Antarctic Ice Sheet into huge ice shelves which provide back stress and stabilize the ice sheet. In this century, loss of ice from Antarctica into the oceans has increased rapidly, reaching ~55% of the contribution of Greenland in the period 2006–2015. Most of the mass loss has occurred from the West Antarctic Ice Sheet and the Antarctic Peninsula, where melting of ice shelves by warming ocean waters has led to dynamic thinning of major outlet glaciers. Slight increases in snowfall offset the mass loss from glaciers and the East Antarctic ice sheet has remained close to balance. In recent years, modelling studies have focused on marine-ice-sheet instabilities, whereby thinning of ice shelves and calving ice fronts leads to grounding line retreat, initiating feedbacks that could make the retreat irreversible. Some researchers think West-Antarctica may already have passed a threshold for irreversible collapse through this process. Presentations in this session can cover, but are not limited to, the following topics:

• Past Antarctic ice sheet dynamics
• Antarctic ice core records of atmospheric history and other paleoclimate data
• Ice sheet internal structure
• Vulnerability of the marine based sectors of the Antarctic Ice Sheet to rising sea level
• Research on subglacial water systems
• Antarctica in the climate system

The cryosphere consists mostly of frozen water and the Earth's snow and ice masses contain 75% of the planet's freshwater. During mid-winter in the Northern Hemisphere, approximately 104 km3 of water are locked up as snow cover on mountain ranges from Alaska to the Himalayas. In the 21st century, climatic warming is projected to increase snow and ice melt in high-mountain areas. The associated hydrological changes will affect rural and urban communities around the Asian water towers and in the Andean mountains. Crop production and hydropower generation, which relies on snowmelt and glacial meltwater in many mountainous regions of the world, will have to adapt to changes in seasonal runoff. Changes in the duration and thickness of lake and river-ice cover in cold regions affect lake evaporation, nutrient/sediment fluxes, aquatic ecosystems and transportation on ice roads. The discharge of rivers flowing through regions of continuous permafrost into the Arctic Ocean is sensitive to Arctic warming and increasing freshwater delivery may influence circulation and sea-ice formation in the Arctic Ocean, which in turn may influence the global climate. Presentations in this session can cover, but are not limited to, the following topics:

• Changes in seasonality of river runoff in snow- and glacier-dominated river basins;
• Projections of future changes in runoff in partly snow-covered and/or glaciated basins;
• Governance/management of river basins in response to changes in snow and ice melt runoff;
• Cryosphere-related flooding;
• Interaction of Arctic rivers with the cryosphere;
• Changes in water quality and ecosystems associated with glacier decline.
• Education, capacity building and international cooperation

Interactions between the oceans and the cryosphere play a key role in the Earth system. The oceans have taken up 90% of the excess heat due to warming of the global atmosphere during the past half century, causing changes in cryospheric components in contact with the ocean water. The retreat of Arctic sea ice is leading to summertime opening of an entirely new open-water ocean on the planet, with far-reaching consequences for the climate system. Thermal expansion of the oceans and the combined annual loss of ice from the world's two large ice sheets and smaller glaciers and ice caps are the largest contributors to sea-level rise, which has accelerated during this century. Warming around Greenland has recently caused an increase in the melting of ice in contact with ocean water but scientists debate whether increased freshwater delivery from the Greenland ice sheet has initiated a slowdown in the formation of deep water in the North Atlantic Ocean. The potential destabilization of sectors of the Antarctic Ice Sheet due to rising sea level is also an important topic in current research. Presentations in this session will highlight the above-mentioned topics, with special emphasis on possible tipping points in the ocean-cryosphere system.

• Transfer of water between the oceans and snow and ice masses on land
• Changes in ocean heat content
• Effects of declining Arctic sea-ice cover on the climate system
• Effects of oceanic warming on tidewater glaciers
• Potential changes in deepwater formation in the N-Atlantic ocean
• A UN Decade of Ocean Science for Sustainable Development 2021–2030: The polar dimension

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