The climate in Greenland – Trap Greenland

The photos to the left: In August 1867, H. Rink photographed the territory around Kobbefjord southeast of Nuuk and then coloured the photographs by hand. To the right are Sebastian Marker Westh’s photographs of the same locations 151 years later. In the top photograph from 2018, the head of the Kobbefjord can be seen to the right. The lower ones are taken facing towards Qaqarssuaq. Note, in for instance, the retreat of glaciers over the period and the trend towards increased vegetation.
H. RINK, 1867, SEBASTIAN MARKER WESTH, 2018

A world invisible to humans appears early in Greenland culture – a world populated by inuat – creatures or states that control the conditions of the physical world. The weather inua was known as an erratic creature that made hunting difficult by producing storms and changeable weather. With the mountainous coastlines, deep fjords and migratory low-pressure systems, changeable weather is part of Greenland. This section describes regional differences in the country’s climate, focusing on the period from approx. 1873 onwards, from which we have systematic climate measurements.

Since the late 18th century, a number of institutions have collected high quality climate data, and the Danish Meteorological Institute (DMI) today publishes their observations annually with time series dating back to 1784 for Nuuk. After 1870, the measurements became more reliable thanks to the scientist H. Rink, among others.

Several national and international organisations are currently collaborating on climate and ecosystem monitoring in Greenland, of which the Danish Meteorological Institute (DMI) and Asiaq (Greenland Survey) are responsible for climate measurements in the coastal regions. In total, the country has about 100 automatic climate stations, covering all the climatic zones. Since the 1970s, satellite measurements have become increasingly important for measuring the climate and physical environment. In particular, changes to the surface, such as the height of glacial ice, vegetation cover and sea ice cover, are being monitored closely.

Atmospheric circulation and wind systems

Above Greenland, air masses generally move from west to east in the troposphere. The reason is the global energy balance that supplies more solar energy at low latitudes than in the polar regions. It creates a pressure difference which, in interaction with the rotation of Earth, drives the general air flow. The air in the northern hemisphere is divided between the cold polar air mass from the north and the warm tropical air mass from the south. The two air masses meet at the polar front. This develops polar lows which are important for the distribution of precipitation. The polar front moves with the seasons and is furthest south in winter, where it is decisive for the weather in northwestern Europe.

Front systems

With a maximum elevation of approx. 3.700 m.a.s.l., Greenland acts as a barrier in the troposphere. Lows formed at the polar front and the related front systems that form west of the country are typically pushed up by this barrier. This results in relatively large amounts of precipitation in the coastal mountain areas and reduced precipitation from the coast towards inland. Depending on how far north the front systems meet the coast, they move either north parallel to the coast, or south around the southern tip of the country. Sometimes the front systems also move across the ice sheet. In addition, the Icelandic low is formed west of Iceland, which transports the relatively warm air masses north past Iceland. The warmer air masses can cause extremely unstable weather conditions in South Greenland and bring with them large amounts of precipitation.

Cooling the air masses

Above the ice sheet, most of the solar radiation is reflected back into the atmosphere. It causes a low temperature and a year-round snow cover in the areas where the ice sheet maintains or increases its mass. The cooling over the ice sheet makes the air masses heavier, thereby moving them downwards from the sloping sides of the ice sheet towards the coast. Such an air flow, called catabatic wind, is frequent on the ice sheet and can cause wind speeds between 6 and 8 m/s. Along the often mountainous coast, a number of wind systems driven by temperature and elevation differences are developing at the same time. For example, shelter effects can occur when wind meets a mountain range, whereby strong, dry foehn winds can develop. A particularly powerful variant is called Piteraq, which means ‘that which attacks you’. The phenomenon is known around Tasiilaq and has led to a tradition of building houses parallel to the wind direction, and with the doorway in the sheltered side.

Fjord winds

Greenland’s complex fjord topography also causes local differences. Here, fjord winds can occur depending on a fjord’s orientation, width and depth. They arise through a combination of pressure differences due to unequal warming of land and sea, as well as a jet effect due to the channelising shape of fjords. The winds can occur relatively quickly and locally, and if you sail in the fjords, it is necessary to assess whether you will be able to make it back home before the waves come, or whether to seek shelter and postpone the return trip.

In winter, most fjords freeze over and sea ice forms around the coasts, except for the stretch between Disko Island and Narsarsuaq on the west coast. The sea ice particularly affects the climate in winter, where, for example, North Greenland at times almost has a continental climate with very low humidity and precipitation and severe cold. During spring and the first part of summer, the ice begins to melt, and the encounter of the cold sea surface with the warmer spring air can form widespread fog along the coasts where there is open water.

Temperature and precipitation

Annual average temperature trend in the period 1875‑2019.
BASED ON DATA FROM DMI

According to Köppen’s climate zone classification, Greenland has a polar climate where all months of the year have an average temperature below 10°C. The ice-free areas have a polar tundra climate. Areas covered by glaciers have a polar ice climate, where the monthly average surface temperature remains below freezing.

Due to large differences in elevation and a relatively short distance between the ice sheet, ice-free land areas and the coast, it is possible to experience incredible climatic variations over distances of just a few kilometres. Overall, both temperature and precipitation increase from north to south, where the growing season is also longer.

Temperature variations over the ice sheet

Over the ice sheet, the air temperature varies mainly with latitude and elevation above sea level. At Summit Station, one of the highest points on the ice sheet, the mean temperature is approx. -31°C (and minimum temperatures all the way down to -70°C), with an annual fluctuation of approx. 30°C. To the west or east of Summit, the mean temperature rises approx. 0.8°C per 10 km. Normally, the temperature drops by 0.5‑1°C per 100 elevation metres, but over the ice sheet there are long periods of low radiation and/or high reflection, which leads to the opposite phenomenon: inversion layers.

The stable temperature conditions result in a widespread and stable high pressure over the ice sheet, which is only interrupted by changed radiation conditions or front systems that sometimes pass. Weather changes in the ice-free areas are often controlled by migratory low-pressure systems that arise from fluctuations in the polar front. When a low pressure passes, it causes a relatively rapid change of weather with slightly rising temperatures, precipitation and sometimes storms.

Temperature variations from north to south

Seasonal variation in mean temperature per month in the period 1990‑2019.
BASED ON DATA FROM DMI

The temperature variation from north to south is most significant in the winter. North of 66°33 north latitude (the Arctic Circle), the sun does not rise above the horizon during parts of the winter period, and thus the earth’s surface does not heat up significantly. In January, for example, the average temperature in Pituffik (76°32N) will be 20°C colder than in southern Qaqortoq (60°43N). As summer approaches and the days gradually become longer (in the northern regions the day length increases for a short period by more than 40 minutes per day), the temperature difference from north to south will decrease.

During the summer period, the area north of the Arctic Circle has midnight sun, and the significant change in radiation means that in July there is only a few degrees difference between Qaqortoq and Pituffik.

Temperature variations from coast to land

You can experience another interesting temperature gradient when you move from the coast over land and towards the ice sheet. In summer, the coastal areas will be cooled by the cold sea, whereas the deep inland valleys at the same latitude may well be 5°C warmer on average. In addition to the cooling from the sea, the difference is also due to a more stable inland climate in summer, with less fog and cloud formation to block for the sunlight. In winter, the coastal areas will be warmer as the sea water is often warmer than the atmosphere, thereby warming land. In areas with widespread sea ice, the climatic difference between coast and inland will be smaller, as the ice isolates the seawater from the atmosphere.

Just like over the ice sheet, inversion layers can form over ice-free land areas. In winter, inversions occur as a result of cooling of the lower air layers due to snow cover, while in summer, they are more likely to form near the coast where the lower air layers are cooled by cold sea water. In some fjords, you see the lushest vegetation in a belt at 100‑200 m above sea level, which is precisely an effect of warmer air masses in summer at this elevation.

Temperature measurements from the end of the 1980s onwards show that Greenland’s ice-free areas have become warmer during that period. Measurements from Qeqertarsuaq on Disko Island show, for example, an increase of approx. 2°C during the period, especially due to warmer winters. At the same time, the temperature change in several parts of the country seems to have stagnated since 2000 – in some places slight cooling is seen in spring and autumn. The measurements show the complexity of temperature changes and that the geographical area and measurement period must be taken into account.

Preciptation and preciptation distribution

The distribution of precipitation is linked to the temperature in the atmosphere and the access to surfaces with water that can evaporate, but is also determined by wind conditions and topography. Warm air masses moving over open water from the south towards Greenland contain large amounts of water vapor, which are released as precipitation when the air meets land and is pushed upwards by the steep mountain sides at the southern tip of the country. In the southwest at Qaqortoq, the annual precipitation is approx. 990 mm and decreases towards the north. In Pituffik, the annual precipitation is thus only approx. 130 mm.

In the northern regions, most of the precipitation will fall as snow, while most of the precipitation in Qaqortoq is rain. This means that to the north, the precipitation accumulates as snow and then melts and flows off to rivers and lakes in spring. This makes a small part of the precipitation available to the terrestrial ecosystems. Where the precipitation falls as snow, it will have an insulating effect on the soil temperature in relation to the air temperature, and thereby it will have an impact on, for example, the presence of permafrost.

Precipitation is also affected by coast-inland dynamics. The colder winter air inland may contain less water vapour. As there are also fewer water surfaces from which the water can evaporate, inland areas will receive less precipitation than coastal areas. Kangerlussuaq on the west coast (67°0N) gets less than 1961‑90 mm of precipitation per year (1961‑1990), whereas Sisimiut (66°56N) at approximately the same northern latitude but 130 km further towards the coast gets approx. 340 mm (1961‑1990). The stable weather in Kangerlussuaq was, moreover, a decisive reason for locating a strategically important airport there.

Projections for the future climate of Greenland

Towards 2100, climate change is expected to increase globally. The Arctic region as a whole is expected to see an intensified temperature rise, mainly due to a meltback of sea ice and its effects. Over both ice-free and glacier-covered areas, temperatures are expected to rise, although the southeastern part may experience a cooling due to weakened cold ocean currents. As a warmer atmosphere may contain more water vapour, warming in Greenland is expected to result in increased autumn and winter precipitation, and more frequent extreme and unpredictable weather events.