Robert Fausto

Starting approximately 6,000 years ago, the introduction of agriculture in Denmark had a marked effect on the landscape as the natural virgin forest that characterized the country was cleared and replaced by farmland. Since then, continued human action has further modified the natural state of the Danish landscape and ecosystems, culminating in a culturally-modified landscape. One result of this historical human activity was a decoupling between landscape and climate in Denmark. Consequently, while it remains possible to use fossil records to reconstruct how the Danish landscape and ecosystems have changed through time, it is extremely difficult to reconstruct how the climate has changed due to the human factor. In response to this limitation, there are no long-term quantitative climate reconstructions available for Denmark. Here, an interdisciplinary approach that combines analysis of modern climate data with the development of climate transfer functions and geospatial analysis is used to quantitatively reconstruct how climate has varied through time in Denmark. The particular climate variables to be examined include July temperature and mean annual precipitation. In addition to producing the first long-term quantitative reconstructions of climate in Denmark, geospatial analysis is also used to generate the first Holocene climate maps for Denmark.

Improving surface boundary conditions for large-scale ice sheet models of Greenland is the main focus and simple parameterizations are used to calculate surface melt, snow densification and meltwater retention. Near-surface air temperature (2m) and its standard deviation from the monthly means over the Greenland Ice Sheet (GrIS) are parameterized using data from automatic weather stations (AWS) located on land and on the ice sheet. The parameterizations are used in a surface mass balance model based on a positive degree day (PDD) approach to simulate the present-day mean surface elevation of the GrIS. The PDD approach accounts for firn warming, rainfall, and refreezing of melt water, with different PDD-factors for ice and snow under warm and cold climate conditions. The snow densification and meltwater retention processes achieves a separation of volume and mass changes of the surface layer to determine the surface melt contribution to runoff. Experiments for present-day conditions ...

ABSTRACT This study uses data from six on-ice weather stations, calibrated MODIS-derived albedo and proglacial river gauging measurements to drive and validate an energy balance model. We aim to quantify the record-setting positive temperature anomaly in 2010 and its effect on mass balance and runoff from the Kangerlussuaq sector of the Greenland ice sheet. In 2010, the average temperature was 4.9 C (2.7 standard deviations) above the 1974–2010 average in Kangerlussuaq. High temperatures were also observed over the ice sheet, with the magnitude of the positive anomaly increasing with altitude, particularly in August. Simultaneously, surface albedo was anomalously low in 2010, predominantly in the upper ablation zone. The low albedo was caused by high ablation, which in turn profited from high temperatures and low winter snowfall. Surface energy balance calculations show that the largest melt excess ( 170 %) occurred in the upper ablation zone (above 1000m), where higher temperatures and lower albedo contributed equally to the melt anomaly. At lower elevations the melt excess can be attributed to high atmospheric temperatures alone. In total, we calculate that 6.6±1.0 km3 of surface meltwater ran off the ice sheet in the Kangerlussuaq catchment in 2010, exceeding the reference year 2009 (based on atmospheric temperature measurements) by 150 %. During future warm episodes we can expect a melt response of at least the same magnitude, unless a larger wintertime snow accumulation delays and moderates the melt-albedo feedback. Due to the hypsometry of the ice sheet, yielding an increasing surface area with elevation, meltwater runoff will be further amplified by increases in melt forcings such as atmospheric heat.