Cryosphere References

• Anthropogenic influences are robustly detected in observed SCE decrease and GHG influence is robustly detected in separation from anthropogenic aerosol and natural forcings with important hydrological and ecological impacts

• SCE decrease shifts solar flux by changing albedo feedbacks and hydrological cycles

• There is a poleward amplification of SCE sensitivity due to warming air temperature through albedo feedbacks

• Most of the late spring SCE decrease over NH from 1970-2019 is attributable to GHG influence which identifies human contributions and GHG influence as separable from other forcing

Palik & Min, 2020

• Observation sites can be used to observe snow catchment areas, rates of snowfall and depth of snow deposits

• Drifting and blowing can be measured with snow drift meters, traps, optical drift meters and radioactive tracing

• Snow depth and SWE can be found using snow stakes, temperature profiles, albedo and free water content

• Areal extents of snow cover can be estimated by ground or air surveys using satellites with long term averages being scientifically important

• Full time observation stations can be installed as well as unmanned stations using remote and telemetry systems

UNESCO et al., 1970

• The area and duration of snow cover are decreasing at 2-4 days per decade in the Arctic which impacts terrestrial ecosystems as it shows a decrease in plant cover and productivity in the last 30 years

• Duration of snow cover is projected to decrease by an addition 10-20% from current levels by mid-century and cold-season precipitation increase by 30-50%

• The Arctic is warming faster than any other region on Earth with feedbacks such as changing albedo and water vapour increase in the atmosphere being important

• Projected changes see coastal areas have fastest and largest declines and this will have implications for food sources, vegetation, habitats, marine ecosystems, water cycling, ocean acidification and atmospheric cycling

Brown et al., 2017

• Climate models suggest rain will be the dominant form of precipitation in the Arctic by 2100 due to atmospheric warming

• Arctic precipitation rates increase much faster than the global rate of 2% per degree instead at 4.5% per degree

• This will impact hydrology, climatology and eco-locality as well as leading to enhanced permafrost melting and methane emissions

Bintanja & Andry, 2017

• There is an overall tendency to decrease in several metrics of snow extremes, particularly in North America and Eurasia due to global warming

• Anthropogenically forced changes in temperature and water vapour have the potential to have major impacts on snowfall as seen in data collected from station observations, remote sensing, satellite and in situ sources

• Snow cover extent, SWE and duration of snow cover see widespread decreases in western US, North America and the Arctic

• These downwards trends are due to a combination of natural and anthropogenic forcings

Kunkel et al., 2016

• Climate change threatens to disturb warm-season water demand by altering fractions of precipitation falling as snow and timing of snowmelt, this threatens food production in basins relying on snowmelt runoff

• This will be particularly important in high-mountain Asia, central Asia, western Russia, western US and southern Andes

• Basins most at risk see 40% of irrigation demand needing to be met by new alternative water supplies under RCP4, adaption of water management and agricultural systems will be critical

Qin et al., 2020

• The timing of spring snowmelt influences patterns of hibernation and reproduction in the population of free-living Arctic ground squirrels in northern Alaska

• Findings show that with late spring snowmelt and early autumn snow melt offspring density was lower before hibernation and the shortening of the active season will compromise juvenile recruitment

Sheriff et al., 2017

• Winter tourism is threatened due to the combined effect of decreasing natural snow amounts and suitable periods for snowmaking 

• 14-25% of ski lifts may be considered in a critical situation in the near future

• Under RCP8.5 there would no longer be any snow reliable ski resorts based on natural conditions in the French Alps of Pyrenees by 2100 with only 24 projected to remain reliable and all in the Alps

Spandre et al., 2019

• Over the last two decades NH snow cover has decreased in extent by 11.7% in June from 1967 to 2010 and did not increase in any month 

• Human influence has been detected in reductions with evidence showing that human influence is extremely likely the dominant cause of observed warming since the mid C20th

• It is very likely NH snow cover will decrease during the C21st due to surface temperature rising, this will decrease by 25% under RCP8.5

IPCC, 2013

• Over the last decades global warming has led to widespread shrinking of the cryosphere with a total loss of 2.5 million km^2 of snow cover in the Arctic from 1967-2018

• Feedbacks continue to amplify global warming and surface temperature increases in the Arctic

• This has impacted terrestrial and freshwater species, animals have had to shift their range, food and water security are negatively impacted with hunting, herding, fishing and gathering practices

• Arctic residents and Indigenous peoples have had to adjust timings of activities to resort to changes in seasonality , hydropower facilities also experience changes and high mountain aesthetic and cultural aspects have been negatively impacted

• Global scale declines in snow cover extent are projected to continue to 2050, under RCP8.5 Arctic spring snow cover will decrease by 50-90%

• Floods and rain-on-snow landslides are projected to occur in new locations and river runoff will change

• There will be further upslope migration by low-elevation species, fire and hydrology regimes will be impacted, human settlements will face increased hazard risks and high mountain recreation will be negatively impacted

IPCC, 2019

• Human influence is very likely to the main driver of the global retreat of glaciers since the 1990s and has been contributing to NH spring snow cover decline since 1950

• Changes in the climate system are becoming larger in direct relation to global warming and this will amplify permafrost thawing and loss of seasonal snow cover

• The global water cycle is intensifying with earlier onset of spring snowmelt and higher peak flows

• All regions are projected to experience further decreases in snow with largest chances at 2 degrees than 1.5 degrees warming

IPCC, 2021

• Between 2007 and 2016 permafrost temperatures increased by 0.29 degrees globally, 0.19 in mountains and 0.37 in Antarctica due to polar amplification of air temperature increases

• Permafrost warming has the potential to amplify global climate change by thawing unlocking previously stored carbon and methane, this will contribute to global warming as well as having further implications for ecosystems, hydrological systems and infrastructure integrity 

• There is a lack of consistent data due to the lack of a standardised data set for temperature observations, a lack of accessible boreholes and data having gaps but the GTN-P data set contributes to reducing uncertainties

• The latent heat effect explains discrepancies seen in permafrost trends in different regions

Biskaborn et al., 2019

• Palsas and peat plateaus are permafrost landforms occurring in subarctic mires that support sensitive ecosystems with significance for vegetation, wildlife, hydrology and carbon cycling; they cover around 850 km^2 of Finmark 

• Between the 1950s and 2010s, there has been a total decrease of 33-71% in the areal extent of the landforms; it has been a continual process with largest changes in the last decade

• Environmental factors leading to the decline are not yet fully understood, but it is likely to be correlated to increases in air temperature, precipitation and snow depth in northern Scandinavia

Borge et al., 2017

• Rapid permafrost thaw in high-altitude and high-elevation areas increases hillslope susceptibility to landsliding by altering geotechnical properties of hillslopes such as reduced cohesion and increased hydraulic connectivity 

• The altered hydrology, vegetation and physical properties of annually thawed soils and bedrock will increase landslide frequency even on low angled slopes

• This will have important impacts on aquatic and terrestrial ecosystems, accelerate ancient carbon release into the atmosphere and pose risks to human settlements and infrastructure particularly in vulnerable communities 

• There is a need for further research to predict and mitigate against these hazards as well as fill in gaps in data through expansion of English-language research, long term monitoring projects and areal data collection as well as quantifying the effect on the carbon budget

Patton et al., 2019

• In recent decades, there is very high confidence that global warming has led to increased permafrost temperatures, this is averaged globally as an increase of 0.29 degrees and will release CO2 as well as destabilising high mountain slopes

• Permafrost thaw has led to ecosystem disturbances, food and water security challenges, negative impacts on human health due to release of contaminants, coastal communities being exposed to hazards and industries threatened due to flooding

• Thaw is projected to continue and will increase further in the second half of the C21st by 24% under RCP2.6 or 69% under RCP8.5 with associated carbon releases

• This will impact mountain hydrology and wildlife, decrease productivity, increase risk of wildfires as well as threatening communication and transport in overlying urban and rural areas

IPCC, 2019

• Over the last decade global warming has led to reductions in Arctic sea ice extent and thickness, it has likely decreased for all months of the year from 1979-2018 with September sea ice decreasing by 13% per decade

• Arctic sea ice has thinned with multi-year ice seeing a decline of 90%, this impacts feedbacks, mid-latitude weather and extreme wave heights 

• Many marine species have undergone shifts in range and seasonal activities due to sea ice change, Arctic net primary production has increased in ice-free waters but many species see habitat losses with cascading impacts on ecosystems

• There are positive impacts with increased ship-based transportation of goods and tourism but coastal communities are exposed to hazards as well as marine ecosystems damaged

• Arctic sea ice extent is projected to decrease further due to surface air temperature increases, at 2 degrees of warming the probability of a sea-ice free September is 10-35%

• This will impact marine animal communities, increase net primary productivity due to upwelling and stratification and impact habitats and prey of marine species

IPCC, 2019

• Proxy records are used to suggest changes in Antarctic sea ice using whaling positions, historic ice charts and direct sea-ice observations

• These conclude a substantial southwards shift in the ice -edge did occur from the 1950s to 1980s with a mid-range estimate of 2.4 degrees south 

• Regional analyses indicate the largest change occurred in the South Atlantic but there is also change detected in the Indian Ocean and Ross Sea

• This is found in accounts of whaling operations describing fleets operating on the ice-edge following it southwards as it retreated each summer whaling season

• There are many criticisms of these ideas with whaling analysis widely regarded as inaccurate

De La Mare, 2009

• Intra-regional differences in the reduction of Antarctic sea ice extent are not widely studied, whaling databases can be used to understand these changes 

• There is a reduction in sea ice occurring in the 1960s mainly in the Weddell sector which change ranging from 3 to 7.9 degrees through summer

• Whaling records are not useful for fine-scale changes but they provide evidence for a heterogenous circumpolar change in sea ice extent consistent with environmental changes detected in the Weddell sector and SH

• This has influenced the ecosystem of the Weddell Sea, particularly krill biomass

Cotte & Guinet, 2007

• Natural drivers of Arctic sea ice variability such as large explosive eruptions or cycles of oceanic circulation are poorly represented, but external forcing can explain up to a third of variability 

• Shorter term responses tend to be in relation to volcanic forcing impacting surface ocean temperatures due to a reduction of solar radiation, but multidecadal changes can be mediated through large-scale ocean dynamic changes in AMOC

• Sea ice expansion coincides with a reduction in AMOC strength due to reduced heat transport to the Arctic allowing sea ice to persist

• Feedbacks can interact with one another in order to amplify and extent their impacts

Halloran et al., 2020

• Deep water formation is the key process driving AMOC, it is started as surface flow in the North Atlantic is driven by the Gulf Stream driving warm salty water north from the equator; as the water travels north it cools, often forming ice and therefore increasing the salinity of the surface water

• Increased salinity increases the density of the water, causing it to sink until it reaches neutral buoyancy, this is the creation of North Atlantic Deep Water (NADW)

• The NADW current flows south to compensate for the north flowing Gulf Stream, the combination of these processes forms AMOC

• The conveyor occurs as NADW is pulled up and warmed via upwelling, this movement of water masses can be considered a linked system or a conveyor belt; the conveyor is considered to have states of ‘off’ and ‘on’ as disturbances in one part of the system can alter processes elsewhere, even causing it to ‘turn off’

Lowe & Walker, 2014

• The Arctic Ocean wave climate is undergoing drastic climate changes due to sea ice retreat due to the increase of swell influence and wave directions changing

• Wave heights are projected to increase up to 6m offshore and 2-3x greater than corresponding 1979-2005 values along coastlines

• These lead to increased wave-driven erosion, inundation and extreme wave events that threaten Arctic coastal communities and existing and emerging infrastructure; this has already been seen in recent years

Casas-Prat & Wang, 2020

• Polar bears use the ice stretching across the ocean surface in the Arctic to access main sources of prey and would be expected to conserve energy in a hibernation-like state in warmer months 

• Anthropogenic climate change is extending the ice free period in the Arctic forcing polar bears to spend more time on land looking for food and not conserving their energy 

• In a studied group in Hudson Bay, they did not hibernate but the food they found also did not meet their calorific needs so the bears lost weight and risk starvation by staying on land 

• The world’s polar bears are endangered by climate change but limiting global warming to the Paris Agreement would help preserve them

France-Presse, 2024

• Combined records show a total glacier mass change of -540 Gt on average from 1819-2019 in Iceland with the equivalent of 1.5 mm of sea level rise

• Almost half the total mass change occurred in 1995-2019 with the most rapid loss from 1994-2010 at around 9.5 Gt per year

• Glaciers in most areas of the world are losing mass due to increasing temperatures associated with global warming, satellite and remote-sensing data shows that these rates are unprecedented

• Although there are substantial temporal and spatial variations, global mass loss trends became clear towards the end of the C20th

• Glaciers in Iceland cover around 10% of the land but many are disappearing, due to the proximity of Iceland to inhabited regions country-wide monitoring has been in place since 1930

Aoalgerisdottir et al., 2020

• The Andes contain a wide variety of topographic and climate conditions resulting in large diversities of ice masses, it contains the largest glacierized area in the SH outside of Antarctica

• The Andean glaciers are placed among the highest contributors to global sea level rise, mitigate against droughts, feed many basins and generate revenue through tourism so their decline is significant 

• They are among the faster shrinking glaciers on Earth with total mass changes from 2000-2018 at around -22.9Gt per year with most negative mass balances in the Patagonian and Tropical Andes

• There is both latitudinal and temporal variabilities in glacier changes responding to climatic events

Dussaillant et al., 2019

• Knowledge of glacier mass balance has expanded since being pioneered around 50 years ago but there is still a problem with short records and biases towards Western Europe and North America as well as wetter conditions

• Glacier mass balance is associated with changes in glacier mass; if accumulation (via snowfall) exceeds ablation (melting and ice carving) the glacier will expand and vise versa

• Changes in glacier mass are accompanied by changes in oceanic mass impacting global sea-levels as well as societies depending on glaciers

• There is no sign of regional trends towards melting that would be expected with warming temperatures, but there is considerable intra-regional variation

• Direct measures have been though stakes and snow pits but it is important to better integrate geodetic and remote sensing methods in the future

Braithwaite, 2002

• High Mountain Asia hosts the largest glacier concentration outside the polar regions and are important contributors to streamflow in one of the most populated areas of the world

• Digital elevation models derived from satellite stereo imagery compute mass balance for 92% of the glacierized area showing total mass change of around -16.3 GT per year from 2000-2016

• There is large intra regional variability with gains of around 1.4 Gt per year in Nyaninqentanghla

• This lower estimate and variability is important for calibrating future models for projecting glacier response to climatic change

Brun et al., 2017

• During 2000 to 2019, glaciers lost a mass of 267 Gt per year equivalent to 21% of observed sea level rise

• There is a mass loss acceleration of 48 Gt per year per decade particularly with glaciers outside of ice sheet peripheries doubling over the last 20 years 

• Glaciers currently lose more mass and at similar to accelerated rates than the Greenland or Antarctic ice sheets separately 

• These estimates can advance understandings of drivers governing distribution of glacier change and be used to design adaptive policy for local and regional scale management of water resources and global-scale mitigation of sea level rise

Hugonnet et al., 2021

• Freshwater scarcity is posed as a global systematic risk

• Two thirds of the global population (4 billion people) live under conditions of severe water scarcity at least one month of the year with nearly half in India and China

• Half a billion people in the world face severe water scarcity all year round 

• Putting caps on water consumption, increasing water-use efficiencies and better shaping of freshwater resources will reduce the threat posed by water scarcity on biodiversity and human welfare

Melonnen & Hoakstra, 2016

• At a regional scale, Greenland ice sheet has experienced accelerating mass loss since 2005 correlated with atmospheric and oceanic warming 

• Mass loss within individual outlet glacier catchments have unexplained variability with mass loss concentrated near the SE and NW

• Glacier thinning is greatest at glacier termini and decreases with distance up-glacier allowing it to be modelled as a kinematic wave, this shows how glacier geology and underlying characteristics impact mass loss

• These variabilities impact predictions of Greenland’s contribution to future sea-level rise

Felikson et al., 2017

• The Antarctic and Greenland Ice Sheets are the last remaining ice sheets since the Last Ice Age 12,000 years ago and store around 68% of Earth’s freshwater

• Between 1992 and 2020, the ice sheets have lost 7.6 trillion tonnes of ice, for Antarctica the West is the most vulnerable due to bedrock being below sea level and Greenland has over 200 major outlet glaciers

• They are influenced through interactions with atmosphere and oceans due to meltwater runoff, warm waters and submarine melting of ice shelves; ice-albedo and brown-pigmented algae feedbacks exacerbate this

• They contribute directly to rising sea levels posing socio-economic implications and risks to people living in low-elevation coastal areas, they also are linked to weakening AMOC and more frequent extreme weather

• They will continue to los mass with greater contributions to global mean sea level, they are vulnerable to positive feedback effects and lose mass rapidly once triggered

Otosaka et al., 2022

• The growth of pigmented algae on ice surfaces increases solar radiation absorption with the effect of contribution an addition 6 Gt of runoff in the SW sector of the GrIS in summer 2017

• In localised patches of high biomass it accelerated melting up to around 26%

• There is a positive feedback loop where higher biomass blooms form in high melt years due to larger areas formed for bloom development and better nutrient availability 

• This is important to estimate Greenland’s sea level contributions in the future an as bare zones and growth seasons for algae will expand in the future

Cook et al., 2020

• GrIS mass loss has recently increased due to enhanced surface melt and runoff critically modulated by surface albedo 

• Greenland’s seasonally fluctuating snowline reduces ice sheet albedo and enhances melt by exposing dark bare ice

• From 2001 to 2017 the process amplified ice sheet melt 5x more than hydrological or biological processes

• In a warmer climate, snowline fluctuations will exert an even greater control on melt due to flatter ice sheet topography at higher elevations

• Snowline elevations are inaccurately predicted forming uncertainties in sea level rise contributions

Ryan et al., 2019

• Limiting warming to 1.5 degrees would halve the land ice contribution to C21st sea level rise relative to current emissions pledges 

• The median decrease is from 25 to 13 centimeters of SLE by 2100 with glaciers responsible for half of the sea level contribution

• Projected Antarctic contribution does not show a clear response to the emissions scenario, but under pessimistic assumptions ice loss could be 5x higher increasing median land ice contribution to 42 cm under current policies and pledges 

• This would severely limit the possibility of mitigating future coastal flooding, adaptation for sea level rise must factor in these uncertainties in Antarctic response especially

Edwards et al., 2021

• Ice sheets and glaciers worldwide have lost mass over the last decades, glaciers worldwide outside of ice sheets have lost mass at an average of 220 Gt per year from 2006-2015

• This impacts slope stability and accelerates sea level rise with ice sheet and glacier contributions as dominant sources 

• This changes abundance, range and establishment of plants and animals as well as habitats and krill distribution in the Antarctic 

• Glacier retreat impacts food and water security due to disrupting agricultural yields, changing water runoff resources and impacting water quality; glacier tourism is also affected

• Global scale glacier mass loss will continue until 2050 with reductions of up to 94 mm under RCP8.5

• This will further decrease stability of slopes, glacier lakes increase as well as floods and river run-off in glacier-fed high mountain basins will change

IPCC, 2019

• Between 2006-2015 the GrIS lost ice mass at an average of around 278 Gt per year and the Antarctic at 155 Gt per year due to rapid thinning and retreat of major outlet glaciers; global mean sea level is increasing as a result

• Mass loss from the Antarctic ice sheet over 2007-2016 tripled compared to 1997-2006 and doubled for Greenland, this is leading to irreversible ice sheet instability

• Ice sheets are projected to lose mass at an increasing rate throughout the C21st, in 2100 the GrIS is projected to contribute 0.15 mm to GMSL rise under RCP8.5 and Antarctic 0.12 mm

• The GrIS is currently contributing more, but Antarctica could become a greater contributor by the end of the C21st due to rapid retreat and instability

IPCC, 2019