Sebastian H. Mernild

Trajectory of the Arctic as an integrated system

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 underway in the Arctic and (2) will shape the future trajectory of the Arctic system. We examine interdependent connections among atmospheric processes, oceanic processes, sea-ice dynamics, marine and terrestrial ecosystems, land surface stocks of carbon and water, glaciers and ice caps, and the Greenland ice sheet. Our emphasis on the interactions between components, both historical and anticipated, is targeted on the feedbacks, pathways, and processes that link these different components of the Arctic system. We present evidence that the physical components of the Arctic climate system are currently in extreme states, and that there is no indication that the system will deviate from this anomalous trajectory in the foreseeable future. The feedback for which the evidence of ongoing changes is most compelling is the surface albedo-temperature feedback, which is amplifying temperature changes over land (primarily in spring) and ocean (primarily in autumn-winter). Other feedbacks likely to emerge are those in which key processes include surface fluxes of trace gases, changes in the distribution of vegetation, changes in surface soil moisture, changes in atmospheric water vapor arising from higher temperatures and greater areas of open ocean, impacts of Arctic freshwater fluxes on the meridional overturning circulation of the ocean, and changes in Arctic clouds resulting from changes in water vapor content.

Present-Day Climate at Zackenberg

Publisher Summary This chapter outlines the most prominent parameters of climate at Zackenberg and focuses on the short-term spatiotemporal variations of these parameters within the valley Zackenbergdalen and along the east coast of Greenland. The individual climatological parameters demonstrate large spatiotemporal variations. The greatest variations occur in winter when the differentiated influence of the solar energy is low or equal to zero, but this is connected to the fact that in the cold winter period, the cyclonic activity is more intensive and frequent than in the warmer summer period. In addition, the temperature contrast between the arctic air and the advected air from the mid-latitudes is highest during this period. In turn, the effect of the underlying surface is not large because snow and sea ice cover almost the entire arctic area. In the warm summer period, the solar radiation is the most important climatological element, and it causes the greatest heterogeneity of the meteorological elements in all spatial scales: micro-, macro-, and topo-climatic. The albedo of the underlying surface that is significantly differentiated increases the influence of solar radiation in the radiation balance. However, because of the attenuated influence of the atmospheric and oceanic circulations and the large areas of the Arctic Ocean and adjacent seas not covered by sea ice, the climatic spatiotemporal differences are lesser in summer than in winter.

Recent warming in Greenland in a long-term instrumental (1881-2012) climatic context: I. Evaluation of surface air temperature records

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 available records (some since 1873). We demonstrate very strong recent warming along the west coast of Greenland, especially during winter (locally > 10 degrees C since 1991), and rather weaker warming on the east Greenland coast, which is influenced by different oceanographic/sea-ice and meteorological synoptic forcing conditions to the rest of Greenland. Coastal Greenland seasonal mean SAT trends were generally 2-6 degrees C, strongest in winter (5.7 degrees C) and least in summer and autumn (both 2.2 degrees C), during 1981-2011/12. Since 2001 Greenland mean coastal SAT increased significantly by 2.9 degrees C in winter and 0.8 degrees C in summer but decreased insignificantly by 1.1 degrees C in autumn and 0.2 degrees C in spring, during a period when there was little net change (<=+/- 0.1 degrees C) in northern hemisphere temperatures. SAT means for the latest 2001-11/12 decade were significantly in excess of those for peak decadal periods during the Early Twentieth Century Warm Period only in summer and winter, and not significantly greater in spring and autumn. Summer SAT increases in southern Greenland for the last 20 years were generally greater for maximum than minimum temperatures. By contrast, in winter, the recent warming was greater for minimum than maximum temperatures. The greatest SAT changes in all seasons are seen on Greenlands west coast. SAT changes on the ice sheet and a key marginal glacier closely followed nearby coastal temperatures over the last 20 years.

Arctic terrestrial hydrology : A synthesis of processes, regional effects, and research challenges

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 ...

Greenland Ice Sheet Surface Mass-Balance Modeling in a 131-Yr Perspective, 1950–2080

Fluctuations in the Greenland ice sheet (GrIS) surface mass balance (SMB) and freshwater influx to the surrounding oceans closely follow climate fluctuations and are of considerable importance to the global eustatic sea level rise. A state-of-the-art snow-evolution modeling system (SnowModel) was used to simulate variations in the GrIS melt extent, surface water balance components, changes in SMB, and freshwater influx to the ocean. The simulations are based on the Intergovernmental Panel on Climate Change scenario A1B modeled by the HIRHAM4 regional climate model (RCM) using boundary conditions from the ECHAM5 atmosphere‐ocean general circulation model (AOGCM) from 1950 through 2080. In situ meteorological station [Greenland Climate Network (GC-Net) and World Meteorological Organization (WMO) Danish Meteorological Institute (DMI)] observations from inside and outside the GrIS were used to validate and correct RCM output data before they were used as input for SnowModel. Satellite observations and independent SMB studies were used to validate the SnowModel output and confirm the model’s robustness. The authors simulated an ;90% increase in end-of-summer surface melt extent (0.483 3 10 6 km 2 ) from 1950 to 2080 and a melt index (above 2000-m elevation) increase of 138% (1.96 3 10 6 km 2 3 days). The greatest difference in melt extent occurred in the southern part of the GrIS, and the greatest changes in the number of melt days were seen in the eastern part of the GrIS (;50%‐70%) and were lowest in the west (;20%‐30%). The rate of SMB loss, largely tied to changes in ablation processes, leads to an enhanced average loss of 331 km 3 from 1950 to 2080 and an average SMB level of 299 km 3 for the period 2070‐80. GrIS surface freshwater runoff yielded a eustatic rise in sea level from 0.8 6 0.1 (1950‐59) to 1.9 6 0.1 mm (2070‐80) sea level equivalent (SLE) yr 21 . The accumulated GrIS freshwater runoff contribution from surface melting equaled 160-mm SLE from 1950 through 2080.

Greenland ice sheet surface melt extent and trends: 1960–2010

Observed meteorological data and a high-resolution (5 km) model were used to simulate Greenland ice sheet surface melt extent and trends before the satellite era (1960–79) and during the satellite era through 2010°. The model output was compared with passive microwave satellite observations of melt extent. For 1960–2010 the average simulated melt extent was 15 ± 5%. For the period 1960–72, simulated melt extent decreased by an average of 6%, whereas 1973–2010 had an average increase of 13%, with record melt extent in 2010. The trend in simulated melt extent since 1972 indicated that the melt extent in 2010 averaged twice that in the early 1970s. The maximum and mean melt extents for 2010 were 52% (∼9.5 × 10 5 km 2 ) and 28% (∼5.2 × 10 5 km 2 ), respectively, due to higher-than-average winter and summer temperatures and lower-than-average winter precipitation. For 2010, the southwest Greenland melt duration was 41–60 days longer than the 1960–2010 average, while the northeast Greenland melt duration was up to 20 days shorter. From 1960 to 1972 the melting period (with a >10% melt extent) decreased by an average of 3 days a− 1 . After 1972, the period increased by an average of 2 days a− 1 , indicating an extended melting period for the ice sheet of about 70 days: 40 and 30 days in spring and autumn, respectively.

Snow Distribution and Melt Modeling for Mittivakkat Glacier, Ammassalik Island, Southeast Greenland

Abstract A physically based snow-evolution modeling system (SnowModel) that includes four submodels—the Micrometeorological Model (MicroMet), EnBal, SnowPack, and SnowTran-3D—was used to simulate five full-year evolutions of snow accumulation, distribution, sublimation, and surface melt on the Mittivakkat Glacier, in southeast Greenland. Model modifications were implemented and used 1) to adjust underestimated observed meteorological station solid precipitation until the model matched the observed Mittivakkat Glacier winter mass balance, and 2) to simulate glacier-ice melt after the winter snow accumulation had ablated. Meteorological observations from two meteorological stations were used as model inputs, and glaciological mass balance observations were used for model calibration and testing of solid precipitation observations. The modeled end-of-winter snow-water equivalent (w.eq.) accumulation increased with elevation from 200 to 700 m above sea level (ASL) in response to both elevation and topographic...

Greenland Freshwater Runoff. Part II: Distribution and Trends, 1960-2010

AbstractRunoff magnitudes, the spatial patterns from individual Greenland catchments, and their changes through time (1960–2010) were simulated in an effort to understand runoff variations to adjacent seas and to illustrate the capability of SnowModel (a snow and ice evolution model) and HydroFlow (a runoff routing model) to link variations in terrestrial runoff with ocean processes and other components of Earth’s climate system. Significant increases in air temperature, net precipitation, and local surface runoff lead to enhanced and statistically significant Greenland ice sheet (GrIS) surface mass balance (SMB) loss. Total Greenland runoff to the surrounding oceans increased 30%, averaging 481 ± 85 km3 yr−1. Averaged over the period, 69% of the runoff to the surrounding seas originated from the GrIS and 31% came from outside the GrIS from rain and melting glaciers and ice caps. The runoff increase from the GrIS was due to an 87% increase in melt extent, 18% from increases in melt duration, and a 5% decr...

Observed runoff, jökulhlaups and suspended sediment load from the Greenland ice sheet at Kangerlussuaq, West Greenland, 2007 and 2008

This study fills the gap in hydrologic measurements of runoff exiting a part of the Greenland Ice Sheet (GrIS), the Kangerlussuaq drainage area, West Greenland. The observations are of value for obtaining knowledge about the terrestrial freshwater and sediment output from part of the GrIS and the strip of land between the GrIS and the ocean, in the context of varying ice sheet surface melt and influx entering the ocean. High-resolution stage, discharge and suspended sediment load show a decrease in runoff of {approx} 25% and in sediment load of {approx} 40% from 2007 to 2008 in response to a decrease in the summer accumulated number of positive degree days. During the 2007 and 2008 runoff season, joekulhlaups are observed at Kangerlussuaq, drained from an ice-dammed lake at the margin of the GrIS.

Strong Downslope Wind Events in Ammassalik, Southeast Greenland

AbstractAmmassalik 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 Forecasts Interim Re-Analysis (ERA-Interim) are used to identify and characterize these strong downslope wind events, which are especially pronounced at a major east Greenland fjord, Sermilik Fjord, within Ammassalik. Their local and regional characteristics, their dynamics and their impacts on the regional sea ice cover, and air–sea fluxes are described. Based on a composite of the events it is concluded that wind events last for approximately a day, and seven to eight events occur each winter. Downslope wind events are associated with a deep synoptic-scale cyclone between Iceland and Greenland. During the events, cold dry air is advected down the ice sheet....