S. H. Mernild

• Prorector and Full Professor (Dr. Scient, and Ph.D.) and Lead Author on IPCC AR6
• Managing Director at Nansen Center in Bergen and Songdal University College

Ice losses from the Greenland and Antarctic ice sheets have accelerated since the 1990s, accounting for a significant increase in the global mean sea level. Here, we present a new 29-year record of ice sheet mass balance from 1992 to 2020 from the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE). We compare and combine 50 independent estima...

Ice losses from the Greenland and Antarctic Ice Sheets have accelerated since the 1990s, accounting for a significant increase in global mean sea level. Here, we present a new 29-year record of ice sheet mass balance from 1992 to 2020 from the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE). We compare and combine 50 independent estimates...

The surface radiation budget is an essential component of the total energy exchange between the atmosphere and the Earth’s surface. Measurements of radiative fluxes near/on ice surfaces are sparse in the polar regions, including on the Greenland Ice Sheet (GrIS), and the effects of cloud on radiative fluxes are still poorly studied. In this work, w...

The amount and spatial extent of Greenland Sea (GS) ice are primarily controlled by the sea ice export across the Fram Strait (FS) and by local seasonal sea ice formation, melting, and sea ice dynamics. In this study, using satellite passive microwave sea ice observations, atmospheric and a coupled ocean-sea ice reanalysis system, TOPAZ4, we show t...

We provide an updated analysis of instrumental Greenland monthly temperature data to 2019, focusing mainly on coastal stations but also analysing ice‐sheet records from Swiss Camp and Summit. Significant summer (winter) coastal warming of ~1.7 (4.4)°C occurred from 1991–2019, but since 2001 overall temperature trends are generally flat and insignif...

Substantial marine, terrestrial, and atmospheric changes have occurred over the Greenland region during the last century. Several studies have documented record‐levels of Greenland Ice Sheet (GrIS) summer melt extent during the 2000s and 2010s, but relatively little work has been carried out to assess regional climatic changes in other seasons. Her...

This chapter provides a review and update of meltwater and Arctic hydrology, and the impact of glacier and ice sheet mass balance contributions to sea-level rise and ocean circulation. It highlights the recent work and results of large-scale modeling of Greenland climate, glaciers, and ice caps and Greenland Ice Sheet (GrIS) mass balances, and Gree...

The surface radiation budget is an essential component of the total energy exchange between the atmosphere and the Earth’s surface. Measurements of radiative fluxes near/on ice surfaces are sparse in the polar regions, including on the Greenland Ice Sheet (GrIS), and the effects of cloud on radiative fluxes are still poorly studied. In this work, w...

Observations and models agree that the Greenland Ice Sheet (GrIS) surface mass balance (SMB) has decreased since the end of the 1990s due to an increase in meltwater runoff and that this trend will accelerate in the future. However, large uncertainties remain, partly due to different approaches for modelling the GrIS SMB, which have to weigh physic...

Katabatic winds drive sea ice export from glaciated fjords across Greenland and other high latitude environments, but few studies have investigated the extent to which they also drive inflow of warm water and whether they have a direct impact on glaciers stability. Using ERA5 reanalysis data, verified by two local weather stations, we create a time...

In recent decades, the Greenland Ice Sheet has been a major contributor to global sea-level rise1,2, and it is expected to be so in the future³. Although increases in glacier flow4–6 and surface melting7–9 have been driven by oceanic10–12 and atmospheric13,14 warming, the degree and trajectory of today’s imbalance remain uncertain. Here we compare...

Abstract. The Greenland Ice Sheet (GrIS) mass loss has been accelerating at a rate of about 20 ± 10 Gt/yr² since the end of the 1990's, with around 60 % of this mass loss directly attributed to enhanced surface meltwater runoff. However, in the climate and glaciology communities, different approaches exist on how to model the different s...

Prediction of high latitude response to climate change is hampered by poor understanding of the role of nonlinear changes in ecosystem forcing and response. While the effects of nonlinear climate change are often delayed or dampened by internal ecosystem dynamics, recent warming events in the Arctic have driven rapid environmental response, raising...

This paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through on-line media, followed by two workshops through which a large number of potential science questions were collated, p...

Key observational indicators of climate change in the Arctic, most spanning a 47 year period (1971–2017) demonstrate fundamental changes among nine key elements of the Arctic system. We find that, coherent with increasing air temperature, there is an intensification of the hydrological cycle, evident from increases in humidity, precipitation, river...

The Arctic Monitoring and Assessment Program (AMAP 2017) report identifies the Arctic as the largest regional source of land ice to global sea-level rise in the 2003-2014 period. Yet, this contextualization ignores the longer perspective from in situ records of glacier mass balance. Here, using 17 (>55°N latitude) glacier and ice cap mass balance s...

We analyzed modeled river runoff variations west of the Andes Cordillera's continental divide for 1979/80-2013/14 (35 years). Our foci were annual runoff conditions, runoff origins (rain, snowmelt, and glacier ice), and runoff spatiotemporal variability. Low and high runoff conditions were defined as occurrences that fall outside the 10th (low valu...

Ice-sheet melting is the primary water source for the proglacial Watson River in southern west Greenland. Discharge from the large, approximately 12,000 km² ice-sheet catchment draining through the Watson River has been monitored since 2006. While this record is of respectable length for a Greenland monitoring effort, it is too short to resolve cli...

The Antarctic Ice Sheet is an important indicator of climate change and driver of sea-level rise. Here we combine satellite observations of its changing volume, flow and gravitational attraction with modelling of its surface mass balance to show that it lost 2,720 ± 1,390 billion tonnes of ice between 1992 and 2017, which corresponds to an increase...

The variables of snow cover extent (SCE), snow cover duration (SCD), and snow albedo (SAL) are primary factors determining the surface energy balance and hydrological response of the cryosphere, influencing snow pack and glacier mass-balance, melt, and runoff conditions. This study examines spatiotemporal patterns and trends in SCE, SCD, and SAL (2...

The spatiotemporal distribution of freshwater runoff from the Greenland ice sheet (GrIS) deter-10 mines the hydrographic and circulation conditions in Greenlandic fjords. The distribution of GrIS first-order atmospheric forcings, surface mass-balance (SMB), including snow/ice melt, and freshwater river discharge from the Kangerlussuaq drainage catc...

New measurements of Watson River sediment and solute concentrations and an extended river discharge record improved by acoustic Doppler current profiler (ADCP) measurements are used to calculate the total sediment and solute transport from a large ice-sheet sector in southern west Greenland. For the 2006–2016 period, the mean annual sediment and so...

26 Knowledge about variations in runoff from Greenland to adjacent fjords and seas is important for 27 the hydrochemistry and ocean research communities to understand the link between terrestrial 28 and marine Arctic environments. Here, we simulate the Greenland Ice Sheet (GrIS) surface mass 29 balance (SMB), including refreezing and retention, and...

An Empirical Orthogonal Function (EOF) variance analysis was performed to map in detail the spatiotemporal variability in individual stake mass-balances (ba) on Mittivakkat Gletscher (MG) – in a region where at present five out of ~20.000 glaciers have mass-balance observations. The EOF analysis suggested that observed ba was summarized by two mode...

Knowledge about variations in runoff from Greenland to adjacent fjords and seas is important for the hydrochemistry and ocean research communities to understand the link between terrestrial and marine Arctic environments. Here, we simulate the Greenland Ice Sheet (GrIS) surface mass balance (SMB), including refreezing and retention, and runoff toge...

30 An Empirical Orthogonal Function (EOF) variance analysis was performed to map and elucidate 31 in detail the spatiotemporal variability in individual stake mass-balances (ba) on the Mittivakkat 32 Gletscher (MG) – in a region where at present five out of ~20.000 glaciers have mass-balance 33 observations. The EOF analysis suggested that observed...

Empirically based studies of glacier meteorology, especially for the Southern Hemisphere, are relatively sparse in the literature. Here, we use an innovative network of highly portable, low-cost thermometers to report on high -frequency (1-min time resolution) surface air temperature fluctuations and lapse rates (LR) in a ~800-m elevational range (...

The Kangerlussuaq area of southwest Greenland encompasses diverse ecological, geomorphic, and climate gradients that function over a range of spatial and temporal scales. Ecosystems range from the microbial communities on the ice sheet and moisture-stressed terrestrial vegetation (and their associated herbivores) to freshwater and oligosaline lakes...

Empirically based studies of glacier meteorology, especially for the Southern Hemisphere, are relatively sparse in the literature. Here, we use an innovative network of highly-portable, low-cost thermometers to report on high-frequency (1-min time resolution) surface air temperature fluctuations and lapse rates (LR) in a ~800-m elevational range (f...

The most recent Intergovernmental Panel on Climate Change assessment report concludes that the Atlantic Meridional Overturning Circulation (AMOC) could weaken substantially but is very unlikely to collapse in the 21st century. However, the assessment largely neglected Greenland Ice Sheet (GrIS) mass loss, lacked a comprehensive uncertainty analysis...

We present the first physical model for the spectral ‘bioalbedo’ of snow, which predicts the spectral reflectance of snow packs contaminated with variable concentrations of red snow algae of varying diameters and pigment concentrations, and then estimates the effect of the algae on snow melt. The bio-optical model estimates the absorption coefficie...

The spatio-temporal freshwater river runoff pattern from individual basins, including their runoff magnitude and change (1979/1980–2013/2014), was simulated for the Andes Cordillera west of the Continental Divide in an effort to understand runoff variations and freshwater fluxes to adjacent fjords, Pacific Ocean, and Drake Passage. The modelling to...

The most recent IPCC assessment report concludes that the Atlantic Meridional Overturning Circulation (AMOC) could weaken substantially, but is very unlikely to collapse in the 21st century. However, the assessment largely neglected Greenland Ice Sheet (GrIS) mass loss, lacked a comprehensive uncertainty analysis, and was limited to the 21st centur...

Glacier surface mass balance (SMB) observations for the Andes Cordillera are limited and therefore estimates of the SMB contribution to sea-level rise are highly uncertain. Here (in Part 3), we simulate glacier surface meteorological and hydrological conditions and trends for the Andes Cordillera (1979/80–2013/14; 35 years), covering the tropical l...

Glacier surface mass-balance measurements on Greenland started more than a century ago, but no compilation exists of the observations from the ablation area of the ice sheet and local glaciers. Such data could be used in the evaluation of modelled surface mass balance, or to document changes in glacier melt independently from model output. Here, we...

For the Andes Cordillera, where observed mass-balance records are sparse, long-term glacier velocity measurements potentially represent a useful tool for assessing glacier health. Utilising manual and automatic feature-tracking techniques applied to Corona, Landsat and ASTER satellite imagery, this paper presents surface velocity fluctuations for G...

Snow cover extent, duration, and properties were simulated (1979/1980–2013/2014) for the Rio Olivares Basin (548 km2) in central Chilean Andes, in an effort to understand conditions and trends (linear) at a basin scale. The National Aeronautics and Space Administration Modern-Era Retrospective Analysis for Research and Applications products, togeth...

ABSTRACT: Snow cover presence, duration, properties, and water amount play a major role in Earth’s climate system through its impact on the surface energy budget. Snow cover conditions and trends (1979–2014) were simulated for South America – for the entire Andes Cordillera. Recent data sets and SnowModel developments allow relatively high-resoluti...

Snow cover presence, duration, properties, and water amount play a major role in Earth's climate system through its impact on the surface energy budget. Snow cover conditions and trends (1979-2014) were simulated for South America - for the entire Andes Cordillera. Recent data sets and SnowModel developments allow relatively high-resolutions of 3-h...

To improve our knowledge of glacier area changes in the central Chilean and Argentinean Andes (32°9′S–33°4′S), two new glacier inventories from 1989 to 2013/14 are compared with a reinterpreted inventory from 1955. Comparisons show glacier area retreat of 30% ± 3% since 1955, decreasing from 134 km 2 to 94 in 2013/14, whilst the annual rate of area...

Analysis of stable oxygen isotope (δ18O) characteristics is a useful tool to investigate water provenance in glacier river systems. In order to attain knowledge on the diversity of δ18O variations in Greenlandic rivers, we examined two contrasting glacierised catchments disconnected from the Greenland Ice Sheet (GrIS). At the Mittivakkat Gletscher...

Terrestrial hydrology is central to the Arctic system and its freshwater circulation. Water transport and water constituents vary, however, across a very diverse geography. In this paper, which is a component of the Arctic Freshwater Synthesis, we review the central freshwater processes in the terrestrial Arctic drainage and how they function and c...

The Mittivakkat Gletscher (MG) mass-balance observation program was initiated in 1995, and is today the only long-term operative local glacier mass balance program in Greenland among several thousands of glaciers peripheral to the ice sheet. For 1995/96–2013/14 the MG mean annual mass-balance (Ba) was -1.00 ± 0.70 m w.e. yr-1, with a linear Ba chan...

Empirical-based studies of glacier meteorology, especially for the Southern Hemisphere, are relatively sparse in the literature. Here we use an innovative network of highly-portable, low-cost thermometers to report on high-frequency (1-min time resolution) surface air temperature variations and lapse rates (LR) in a ~800-m elevational range across...

Analysis of stable oxygen isotope (δ18O) characteristics is a useful tool to investigate water provenance in glacier river systems. In order to attain knowledge on the diversity of spatio-temporal δ18O variations in glacier rivers, we have examined three glacierized catchments in Greenland with different areas, glacier hydrology and thermal regimes...

The distribution of terrestrial surface runoff to Ilulissat Icefjord, West Greenland, is simulated for the period 2009–2013 to better emphasize the spatio-temporal variability in freshwater flux and the link between runoff spikes and observed hydrographic conditions at the Greenland Ice Sheet tidewater glacier margins. Runoff model simulations were...

Southern Greenland is characterized by a number of low-level high wind speed weather systems that are the result of topographic flow distortion. These systems include barrier winds and katabatic flow that occur along its southeast coast. Global atmospheric reanalyses have proven to be important tools in furthering our understanding of these orograp...

Observations obtained by ringed seals (Pusa hispida) near tidewater glacier margins in Ilulissat Icefjord and Sermilik Fjord provide a novel platform to examine the otherwise inaccessible waters beneath the dense ice melangé within the first 0–10 km of the calving front – to advance our understanding of the hydrographic conditions of the waters nea...

Surface albedo is defined as the reflected fraction of incoming solar shortwave radiation at the surface. On Greenland’s Mittivakkat Gletscher the mean glacier-wide MODIS-estimated albedo dropped by 0.10 (2000–2013) from 0.43 to 0.33 by the end of the mass balance year (EBY). Hand-held albedo measurements as low as 0.10 were observed over debris-co...

Here we present ground-penetrating radar measurements of Mittivakkat Gletscher, southeast Greenland, to estimate an empirical volume–area scaling relationship at an individual glacier. Between a previous direct volume survey in 1994 and one in 2012, the glacier volume has decreased from 2.02 km3 to 1.44 km3 while the study area has decreased from 1...

Large, deep-keeled icebergs are ubiquitous in Greenland's outlet glacial fjords. Here, we use the movement of these icebergs to quantify flow variability in Sermilik Fjord, southeast Greenland, from the ice mélange through the fjord to the shelf. In the ice mélange, a proglacial mixture of sea ice and icebergs, we find that icebergs consistently tr...

Global volume-area scaling relations are commonly used to estimate regional glacier volume and their potential contribution to sea-level rise. However, little is known about volume-area scaling of individual glaciers where local glaciological conditions and climatic disequilibrium cause deviations from global steady-state scaling. Here, we present...

Albedo is one of the parameters that govern energy availability for snow and ice surface ablation, and subsequently the surface mass balance conditions of temperate glaciers and ice caps (GIC). Here, we document snow and ice albedo changes for Mittivakkat Gletscher (MG) in Southeast Greenland (2000–2013), for which an 18 year record of direct surfa...

In this study, observed annual mass-balance data series from 1970 to 2009 for 29 land-terminating glaciers and ice caps in the northern North Atlantic region are presented to highlight their spatio-temporal variability. The glaciers and ice caps mass-balance data are compared with various zonal latitude bands of regional near-surface air temperatur...

Mass changes and mass contribution to sea level rise from glaciers and ice caps (GIC) are key components of the earth's changing sea level. GIC surface mass balance (SMB) magnitudes and individual and regional mean conditions and trends (1979-2009) were simulated for all GIC having areas greater or equal to 0.5 km2 in the Northern Hemisphere north...

We use observed air temperature data series from 14 meteorological stations in coastal Greenland (located all around the Greenland Ice Sheet) for 1960–2010, where long-term records for five of the stations extend back to 1890, to illustrate the annual and monthly temporal and spatial distribution of temperature extremes, with the main focus on the...

The NASA announcement of record surface melting of the Greenland ice sheet in July 2012 led us to examine the atmospheric and oceanic climatic anomalies that are likely to have contributed to these exceptional conditions and also to ask the question of how unusual these anomalies were compared to available records. Our analysis allows us to assess...

:Here, we present an analysis of monthly, seasonal, and annual long-term precipitation time-series compiled from coastal meteorological stations in Greenland and Greenland Ice Sheet (GrIS) ice cores (including three new ice core records from ACT11D, Tunu2013, and Summit2010). The dataset covers the period from 1890 to 2012, a period of climate warm...

Ammassalik in southeast Greenland is known for strong wind events that can reach hurricane intensity and cause severe destruction in the local town. Yet, these winds and their impact on the nearby fjord and shelf region have not been studied in detail. Here, data from two meteorological stations and the European Centre for Medium-Range Weather Fore...

Here, we present a new glacier inventory for the Rio Olivares catchment (531 km2), Central Chilean Andes (33°14‘44 S, 70°07‘26 V). Area changes for 145 glaciers were analyzed for the period 1955 through 2013 based on terrestrial photogrammetry, aerial photography, and satellite imagery. The results show that the glacier area, excluding rock glacier...

The majority of glaciers and ice caps (GIC) are out of balance with present day climate conditions. In order to return to equilibrium, these GIC must lose mass and retreat to higher elevations. Here, we present mass balance and accumulation-area ratio (AAR, the fractional glacier area where accumulation exceeds ablation) data from 20 observed GIC i...

Mass-balance and freshwater runoff observations from the Southern (SPI) and Northern Patagonia ice caps (NPI) are limited. Here, we present winter and summer mass-balances and runoff simulations for both ice caps. The model development and setup permit relatively high-resolution (500-m horizontal grid; 3-h time step) SPI and NPI estimates for 1979...

Mass changes and mass contribution to sea-level rise from glaciers and ice caps (GIC) are key components of Earth’s changing sea-level. GIC surface mass balance (SMB) magnitudes, and individual and regional mean conditions and trends (1979–2009) were simulated for all GIC having areas greater or equal to 0.5 km2 in the Northern Hemisphere north of...

We document changes for Mittivakkat Gletscher, the peripheral glacier in Greenland with the longest field-based observed mass-balance and surface velocity time series. Between 1986 and 2011, this glacier changed by –15% in mean ice thickness and –30% in volume. We attribute these changes to summer warming and lower winter snow accumulation. Vertica...

Albedo is one of the parameters that governs energy availability for snow and ice surface ablation, and subsequently the surface mass balance conditions of temperate glaciers and ice caps (GIC). Here, we document snow and ice albedo changes on Mittivakkat Gletscher in Southeast Greenland, the only local glacier in Greenland for which there exist lo...

In this study, observed annual mass-balance data series from 1970 to 2009 for 29 land-terminating glaciers and ice caps (GIC) in the northern North Atlantic region are presented to highlight their spatio-temporal variability. The GIC mass-balance data are compared with various zonal latitude bands of regional near-surface air temperature time serie...

Although much remains to be learned about the Arctic and its component processes, many of the most urgent scientific, engineering, and social questions can only be approached through a broader system perspective. Here, we address interactions between components of the Arctic system and assess feedbacks and the extent to which feedbacks (1) are now...

Identification of the transient snowline (TSL) from high spatial resolution Landsat imagery on Mittivakkat Gletscher, Southeast Greenland, was used in identification of ablation rates, the equilibrium line altitude (ELA), and the accumulation-area ratio (AAR). The rate of rise of the TSL during the ablation season on a glacier where the balance gra...

Mass-balance and freshwater runoff observations from land-terminating glaciers and ice caps (GIC) are limited in high-latitude regions. Here, we present winter and summer mass-balances and runoff simulations for every GIC with surface areas greater than or equal to 1 km 2 in the Northern Hemisphere north of 25 deg. N latitude. The model development...

Ample evidence indicates the Greenland climate and hydrological cycle is changing. Fluctuations in mass balance and freshwater runoff from the Greenland Ice Sheet (GrIS) and Greenland follow climate fluctuations. Runoff magnitudes, the spatial patterns from individual Greenland catchments, and their changes through time (1960–2010) were simulated u...

Satellite imagery (Landsat) was applied to elucidate area fluctuations of land-terminating glaciers and ice caps (GIC) in Circumpolar Arctic. The imagery gives us the possibility to map "snapshots" and the averaged behavior of glacier changes for the past 25 years (mid-1980s to present) for identified GIC during a period of climate warming. Satelli...

Most glaciers and ice caps (GIC) are out of balance with the current climate. To return to equilibrium, GIC must thin and retreat, losing additional mass and raising sea level. Because glacier observations are sparse and geographically biased, there is an undersampling problem common to all global assessments. Here, we further develop an assessment...

Most glaciers and ice caps (GIC) are out of balance with the current climate. To return to equilibrium, GIC must thin and retreat, losing additional mass and raising sea level. Because glacier observations are sparse and geographically biased, there is an undersampling problem common to all global assessments. Here, we further develop an assessment...

Identification of the transient snowline (TSL) from high spatial resolution Landsat imagery on Lemon Creek Glacier (LCG), southeast Alaska, USA, and Mittivakkat Gletscher (MG), southeast Greenland, is used to determine snow ablation rates, the equilibrium-line altitude (ELA) and the accumulation-area ratio (AAR). The rate of rise of the TSL during...

An automated layer counting technique is developed to estimate the chronology of a marine sediment core and this technique is validated with Pb210 chronology. The marine sediment core was sampled in front of the delta of Mittivakkat Glacier meltwater river in the Sermilik Fjord, SE Greenland, and is a proxy of the sediment delivery from a glacial d...

Most glaciers and ice caps (GIC) are out of balance with the current climate. To return to equilibrium, GIC must thin and retreat, losing additional mass and raising sea level. Because glacier observations are sparse and geographically biased, there is an un-dersampling problem common to all global assessments. Here, we further develop an 5 assessm...

Land-terminating glaciers and ice caps (hereafter called glaciers) disconnected and dynamically independent from the Greenland Ice Sheet (GrIS) and the Antarctic Ice Sheet (AIS) are generally shrinking, tracing changes in climatic conditions (e.g. Cogley, 2012). Estimation of losses of terrestrial ice mass from the GrIS, AIS and gla-ciers to e.g. t...

We use observed air temperature data series from fourteen meteorological stations in coastal Greenland (located all around the Greenland Ice Sheet (GrIS)) for 1960-2010, where long-term records for five of the stations extend back to 1890, to illustrate the annual and monthly temporal and spatial distribution of temperature extremes. We find that t...

Correlation analysis of Greenland coastal weather station temperatures against the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO) indices for the summer season (when Ice Sheet melt and runoff occur) reveals significant temporal variations over the last 100 years, with periods of strongest correlations in the early...

We present an updated analysis of monthly means of daily mean, minimum and maximum surface air temperature (SAT) data from Greenland coastal weather stations and from a long-running site on the Greenland ice sheet, and analyse these data for evidence of climate change, especially focusing on the last 20 years but using the whole periods of availabl...

The shrinking of land-terminating glaciers and ice caps (GIC) has been documented in high-latitude regions, even though repeat observations upon which to base such studies have been limited in space. Here, we present a new record of satellite-derived area changes for 321 land-terminating GIC throughout Pan-Arctic and for the W. Canada and W. US, wi...

Here, we document changes for the Mittivakkat Gletscher, the glacier in Greenland (disconnected to the Greenland Ice Sheet, GrIS) having the longest observed mass balance and surface velocity time series (since 1995). Between 1986 and 2011, this glacier decreased by 15% in mean ice thickness and 30% in volume. We attribute these changes to summer w...

A gridded linear-reservoir runoff routing model (HydroFlow) was developed to simulate the linkages between runoff production from land-based snowmelt and icemelt processes and the associated freshwater fluxes to downstream areas and surrounding oceans. HydroFlow was specifically designed to account for glacier, ice sheet, and snow-free and snow-cov...