Temperature in Polar regions: Arctic and Antarctic

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General

The two polar regions are usually identified as key regions for monitoring global climate change, because the surface air temperature is expected to increase especially rapid in these two regions along with the ongoing increase of atmospheric CO2. Below we therefore focus on past and climate change in both polar regions during the period with meteorological observations; first of all illustrated by observed changes in mean annual surface air temperature for regions north of 70oN and south of 70oS, respectively.

Mean annual surface air temperature (MAAT) anomaly 70-90oN compared to the WMO normal period 1961-1990, as estimated by Hadley CRUT. HadCRUT4 temperature data from the Climatic Research Unit (CRU) has been used to prepare the diagram. The number of high latitude meteorological stations is low in the early part of the 20th century, but increased from 1923 and especially 1933. Last year shown: 2013. Latest update: 10 February 2014.

 

Please note: HadCRUT4 has improved data coverage in the Arctic, compared to the previous version HadCRUT3. As the planetary circumference changes rapidly with increasing latitude, each 5ox5o grid cell has been area corrected before calculating the annual mean. This is in contrast to the procedure followed by Gillet et al. 2008, who gave equal weight to data in each 5ox5o grid cell when calculating means, with no consideration to the area effect of increasing latitude. 

 

Mean annual surface air temperature (MAAT) anomaly 70-90oS compared to the WMO normal period 1961-1990, as estimated by Hadley CRUT. The international geophysical year 1957 marks the initiation of widespread meteorological observations in the Antarctic. HadCRUT4 temperature data from the Climatic Research Unit (CRU) has been used to prepare the diagram. Last year shown: 2013. Latest update: 10 February 2014.

 

Please note: HadCRUT4 has improved data coverage in the Arctic, compared to the previous version HadCRUT3. As the planetary circumference changes rapidly with increasing latitude, each 5ox5o grid cell has been area corrected before calculating the annual mean. This is in contrast to the procedure followed by Gillet et al. 2008, who gave equal weight to data in each 5ox5o grid cell when calculating means, with no consideration to the area effect of increasing latitude. 

 

Global monthly average lower troposphere temperature since 1979 for the North Pole and South Pole regions, based on satellite observations (University of Alabama at Huntsville, USA). This graph uses data obtained by the National Oceanographic and Atmospheric Administration (NOAA) TIROS-N satellite, interpreted by Dr. Roy Spencer and Dr. John Christy, both at Global Hydrology and Climate Center, University of Alabama at Huntsville, USA. Thick lines are the simple running 37 month average, nearly corresponding to a running 3 yr average. Click here to read about data smoothing. Click here to download the entire series of UAH MSU global monthly lower troposphere temperatures since December 1978. Reference period 1981-2010. Last month shown: November 2014. Last diagram update: 4 December 2014.

  • Click here to download the entire series of UAH MSU global monthly lower troposphere temperatures since December 1978.

  • Click here to read about data smoothing.

 

Global monthly average lower troposphere temperature since 1979 for the northern (60-82.5N) and southern (60-70S) polar regions, according to Remote Sensing Systems (RSS). These graphs uses data obtained by the National Oceanographic and Atmospheric Administration (NOAA) TIROS-N satellite, and interpreted by Dr. Carl Mears (RSS). Thick lines are the simple running 37 month average, nearly corresponding to a running 3 yr average. Click here for a description of RSS MSU data products. Please note that RSS January 2011 changed from Version 3.2 to Version 3.3 of their MSU/AMSU lower tropospheric (TLT) temperature product. Click here to read a description of the change from version 3.2 to 3.3, and previous changes. Last month shown: November 2014. Last diagram update: 4 December 2014.

  • Click here to download the entire series of RSS MSU global monthly lower troposphere temperatures since January 1979.

  • Click here to read about data smoothing. 

 

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Recent temperature changes in the two polar regions

The above diagrams show changes of average temperatures only. To enable a more detailed analysis of recent spatial surface air temperature changes in the two polar and adjoining regions, you will find two tables below, representing areas north of 50oN and south of 50oS, respectively. In these tables recent monthly surface air temperatures are compared with the average temperature for the period 1998-2006, to monitor any general recent change of temperature, up or down. As mentioned above, global climate models forecast that surface air temperatures should increase rapidly now and in the future due to increasing atmospheric CO2, especially in the two polar regions. 

Click on one of the small maps, and a larger map in polar projection will open in a new window, showing the temperature difference between the month chosen and the monthly average for the reference period 1998-2006. Geographical regions with higher temperatures the month chosen are indicated by warm colours, regions with lower temperature with blue colours on the scale (degrees C) to the right in the diagrams. The number in the lowermost left corner represents the temperature deviation for the month shown relative to the average 1998-2006. The time series of these monthly values are shown in the diagram below each table.

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Arctic recent weather

Recent surface temperatures north of 15oN according to the Earth System Research Laboratory at NOAA. Temperatures are given in degrees Celsius (scale to the left). Click here to see the original diagram or to check for a more recent update than shown above. Date: 9 December 2014.

 

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Arctic monthly surface air temperature anomalies versus average 1998-2006 north of 50oN

 

YEAR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ANNUAL
2014    
2013
2012
2011
2010
2009
2008
2007
2006
2005

Spatial distribution of monthly surface air temperature deviation north of 50oN in relation to the average for the period 1998-2006. Warm colours indicates areas with higher temperature than the 1998-2006 average, while blue colours indicate lower than average temperatures. By adopting this recent reference period, instead of the official WMO period 1961-1990, is will gradually be possible to visualize if 1998-2006 represents a peak period for the global average temperature, or if modern temperatures are increasing to a even higher level. In the individual diagrams the month is indicated by a number: 1 = January, 2 = February, etc. Click on the individual small diagrams to open full-size diagrams. Please also read the notes here before interpreting the diagrams. Similar spatial temperature diagrams showing the equatorial regions can be seen by clicking here. Data source: NASA Goddard Institute for Space Studies (GISS). Last diagram update 17 December 2014.  

 

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Arctic monthly surface air temperatures north of 70N

Diagram showing area weighted Arctic (70-90oN) monthly surface air temperature anomalies (HadCRUT4) since January 2000, in relation to the WMO normal period 1961-1990. The thin blue line shows the monthly temperature anomaly, while the thicker red line shows the running 37 month (c.3 yr) average. Last month shown: October 2014. Last diagram update: 4 December 2014.

 

 

Diagram showing area weighted Arctic (70-90oN) monthly surface air temperature anomalies (HadCRUT4) since January 1957, in relation to the WMO normal period 1961-1990. The thin blue line shows the monthly temperature anomaly, while the thicker red line shows the running 37 month (c.3 yr) average. Last month shown: October 2014. Last diagram update: 4 December 2014.

 

 

Diagram showing area weighted Arctic (70-90oN) monthly surface air temperature anomalies (HadCRUT4) since January 1920, in relation to the WMO normal period 1961-1990. The thin blue line shows the monthly temperature anomaly, while the thicker red line shows the running 37 month (c.3 yr) average. Because of the relatively small number of Arctic stations before 1930, month-to-month variations in the early part of the temperature record are larger than later. The period from about 1930 saw the establishment of many new Arctic meteorological stations, first in Russia and Siberia, and following the 2nd World War, also in North America. The period since 2000 is warm, about as warm as the period 1930-1940. Last month shown: October 2014. Last diagram update: 4 December 2014.

 

 

Note to the three Arctic temperature diagrams above: As the HadCRUT4 data series has improved high latitude data coverage (compared to the HadCRUT3 series) the individual 5ox5o grid cells has been weighted according to their surface area. This is in contrast to Gillet et al. 2008 which calculated a simple average, with no consideration to the surface area represented by the individual 5ox5o grid cells.

 

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Arctic daily surface air temperatures north of 80N

 

Click here to see daily mean temperature north of 80oN, as a function of the day of year. Source: The Danish Meteorological Institute (DMI), Centre for Ocean and Ice.

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Arctic long meteorological data series

Long Arctic surface annual air temperature series: Fairbanks (Alaska), Nuuk (Greenland), Akureyri (Iceland), Svalbard (Norway), Ostrov Dikson (Siberia), and Hatanga (Siberia). Annual values were calculated from monthly average temperatures. Almost unavoidably, some missing monthly data were encountered in some of the series. In such cases, the missing values were generated as either 1) the average of the preceding and following monthly values, or 2) the average for the month registered the preceding year and the following year. The thin blue line represents the mean annual air temperature, and the thick blue line is the running 5 year average. Click here to read about data smoothing. Data source: NASA Goddard Institute for Space Studies (GISS) and RimFrost. Last year shown: 2013. Last update 19 October 2014.

 

 

For the Arctic, a major focus has been the Arctic Climate Impact Assessment. Based on the results from an average of the output from five climate models, which were also used for the IPCC, temperature projections were produced for the next century. The models all predicted a steady rise in annual mean surface air temperature with, on average, temperatures being 4oC higher by 2100, corresponding to an average decadal temperature increase of 0.4oC (World Meteorological Organization 2007).

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Antarctic recent weather

Recent weather in the Antarctic and adjoining regions according to the University of Cologne, on 17 September 2013. Observation time (GMT) is indicated above the diagram, to the right. Surface air temperature is shown by numbers (oC). Wind direction and strength is shown by white linear symbols. Click here for a list of other symbols used. In this list symbol numbers are constructed as row-column in the table shown; e.g. symbol number 86 corresponds to row number eight, column number six (snow shower(s), moderate or heavy). Click here to see the original diagram or to check for a more recent update than shown above.

 

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Antarctic monthly surface air temperature anomalies versus average 1998-2006 south of 50oS

 

YEAR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ANNUAL
2014    
2013
2012
2011
2010
2009
2008
2007
2006
2005

Spatial distribution of monthly surface air temperature deviation south of 60oS in relation to the average for the period 1998-2006. Warm colours indicates areas with higher temperature than the 1998-2006 average, while blue colours indicate lower than average temperatures. By adopting this recent reference period, instead of the official WMO period 1961-1990, is will gradually be possible to visualize if 1998-2006 represents a peak period for the global average temperature, or if modern temperatures are increasing to a even higher level. In the individual diagrams the month is indicated by a number: 1 = January, 2 = February, etc. Click on the individual small diagrams to open full-size diagrams. Similar spatial temperature diagrams showing the equatorial regions can be seen by clicking here. Please also read the notes here before interpreting the diagrams. Data source: NASA Goddard Institute for Space Studies (GISS). Last diagram update 17 December 2014. 

 

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Antarctic monthly surface air temperatures south of 70S

Diagram showing area weighted Antarctic (70-90oS) monthly surface air temperature anomalies (HadCRUT4) since January 2000, in relation to the WMO normal period 1961-1990.  The thin blue line shows the monthly temperature anomaly, while the thicker red line shows the running 37 month (c.3 yr) average. Last month shown: October 2014. Last diagram update: 4 December 2014.

 

Diagram showing area weighted Antarctic ( 70-90oS) monthly surface air temperature anomalies (HadCRUT4) since January 2000, in relation to the WMO normal period 1961-1990.  The thin blue line shows the monthly temperature anomaly, while the thicker red line shows the running 37 month (c.3 yr) average. The year 1957 was an international geophysical year, and several meteorological stations were established in the Antarctic because of this. Before 1957, the meteorological coverage of the Antarctic continent is poor. Last month shown: October 2014. Last diagram update: 4 December 2014.

 

 

Note to the two Antarctic temperature diagrams above: As the HadCRUT4 data series has improved high latitude data coverage (compared to the HadCRUT3 series) the individual 5ox5o grid cells has been weighted according to their surface area. This is in contrast to Gillet et al. 2008 which calculated a simple average, with no consideration tof the surface area represented by the individual 5ox5o grid cells.

 

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Antarctic long meteorological data series

 

Long Antarctic surface annual air temperature series: Halley, Vostok, Amundsen-Scott and McMurdo. Annual values were calculated from monthly average temperatures. Almost unavoidably, some missing monthly data were encountered in some of the series. In such cases, the missing values were generated as either 1) the average of the preceding and following monthly values, or 2) the average for the month registered the preceding year and the following year. The thin blue line represents the mean annual air temperature, and the thick blue line is the running 5 year average. Click here to read about data smoothing. Data source: NASA Goddard Institute for Space Studies (GISS). Last year shown: 2013. Last update 19 October 2014.

The climate models runs for the IPCC's Fourth Assessment Report suggest that, with an increase in greenhouse gases of 1 percent per year, annual mean surface air temperatures in the Antarctic sea-ice zone over the 21st century would increase by 0.2-0.3oC per decade (WMO 2007). There would be a corresponding decrease in the extent of sea ice. Large parts of the high interior of the Antarctic would experience surface air temperature rises of more than 0.3oC per decade (World Meteorological Organization 2007).

 

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Data source

All diagrams shown in the tables above were prepared using gridded data downloaded from the public domain NASA Goddard Institute for Space Studies (GISS) web page. For  surface interpolationof the gridded data a kriging algorithm was used, plotting all data in a polar projection map. The kriging procedure attempts to express trends and is widely considered one of the more flexible interpolation methods, producing a smooth map with few ‘bull eyes’. It is usually recommended for gridding almost any type of data set, especially data sets with a heterogeneous point distribution, such as characterising the present data set.

The GISS temperature database attempts to provide a more complete representation of the Arctic region than most other databases, which is the reason for using this particular database for preparation of temperature diagrams on this webpage. It does so by taking spatial correlation into account through extrapolating and interpolating in space. The real datapoints, however, remains identical to those used by other fine databases.

It should be noted that the observation network is not charactericed by high or equal density within the two polar regions. Thus, temperature changes displayed within the central part of the Arctic Ocean should be interpreted with great care only. To a high degree contour patterns in such areas with less than optimal density of datapoints may represent interpolation artefacts derived from the interpolation procedure itself.

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Polar regions as key regions for global climate change

Changes in the Polar atmosphere-ice-ocean system observed in recent years have sparked intense discussions as to whether these changes represent episodic events or long-term shifts in the Arctic environment. Late 20th century concerns about future climate change mainly stem from the increasing concentration of greenhouse gasses in the atmosphere. Existing knowledge on Quaternary climate and Global Climate Models (GCMs) predict that the effect of any ongoing and future global climatic change should be amplified in the polar regions due to feedbacks in which variations in the extent of glaciers, snow, sea ice and permafrost as well as atmospheric greenhouse gases play key roles. In addition, variations in the thickness of sea-ice tend to reinforce surface atmospheric temperature anomalies by altering the heat and moisture transfer from the ocean to the atmosphere. Thus, during the last 15 years the Arctic has gained a prominent role in the scientific debate regarding global climatic change.

The alleged enhanced temperature increase at high latitudes is mainly due to two theoretical greenhouse mechanisms:

  • Firstly, atmospheric carbon dioxide (CO2) has its greatest absorption of infrared radiation (IR) at sub-zero temperatures, as its absorption bands lie in the 12-16 micron wavelength band, corresponding to the wavelength of strongest IR surface emission from polar ice and snow. At higher temperatures, the typical wavelength of the strongest IR surface transmission is less than 12 microns, and therefore less affected by CO2. At temperatures near the average surface temperature of the Earth (c. 15°C), the strongest emission wavelength is around 10 microns, a wavelength which is largely unaffected by greenhouse gases. This is the so-called `radiation window' of the atmosphere where IR radiation from the surface escapes freely to the space.

  • Secondly, by far the most powerful atmospheric greenhouse gas is water vapour. Water vapour shares many overlapping absorption bands with CO2 and therefore an increase or decrease in atmospheric CO2 has limited effect on the overall rate of IR absorption in those overlapping regions, if water vapour is present in sufficient quantity. In the Polar Regions , the air is dry due to prevailing low temperatures, allowing CO2 to exert a much greater influence than would be possible in warmer and moister air masses at lower latitudes. Here water vapour saturates the absorption wavebands to the point where changes in CO2 have little effect. In addition to the enhanced greenhouse effect, Arctic climate is influenced by a powerful positive feedback mechanism, the temperature-albedo feedback, tending to amplify any initial temperature change. Rising temperatures will usually increase melting of snow and sea ice, reducing surface reflectance, thereby increasing solar absorption, which raises temperatures, and so on. Conversely, if climate cools, less snow and ice melts in summer, raising the albedo and causing further cooling as more solar radiation is reflected rather than absorbed.

For the above reasons, an important enhanced greenhouse surface ‘fingerprint’ is usually considered to be enhanced warming in the polar and sub-polar regions, less warming in the tropics and sub-tropics, and least warming in equatorial regions. This is the basic reason for much renewed research interest in Arctic regions, and recent sub-continental scale analysis of meteorological data obtained during the observational period apparently lends empirical support to the alleged high climatic sensitivity of the Arctic (Giorgi 2002). Analyses by different GCMs specifically of an enhanced greenhouse effect all suggest that the Polar Regions now should be experiencing a much larger warming than registered in lower latitudes. Polyakov et al. (2002a, 2002b), however, recently presented updated observational trends and variations of Arctic climate and sea ice cover during the 20th century, which questions the modelled polar amplification of temperature changes observed by surface stations at lower latitudes. The cryosphere is a prominent feature of the Polar Regions, represented by snow, glaciers, sea ice and permafrost. The physical properties of snow and ice include high reflectivity, high latent heat required converting ice to liquid water, and the low thermal conductivity of snow and ice; these factors all contribute significantly to the characteristics of Polar climates.

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Meteorological conditions in the Arctic

 

Winter conditions in the valley Fardalen, central Spitsbergen, April 10, 2007.

 

Modern meteorological conditions and climate in the Arctic is to a high degree regulated by the advection of warm North Atlantic waters into the Nordic Seas, the Norwegian- and the Greenland Sea. Maritime climate conditions therefore prevail over much of the Arctic Ocean, coastal Alaska, Iceland, northern Norway and adjoining parts of Russia.  In these areas, winters are cold and windy. Summers are cloudy and cool with mean temperatures ranging from 4 to 8oC over land areas. Annual precipitation is generally between 600 mm and 1300 mm (w.e.), with a cool season maximum (largely snowfall) and about five to seven months of continuous snow cover (e.g., Berry et al. 1993; Barry and Chorley 1998). Shallow permafrost (0-250 m) characterise these regions. Forests are usually absent or found only close to sea level in sheltered positions due to low summer temperatures and/or windy conditions (Humlum and Christiansen 1998).

Arctic interior continental climates have more severe winters and precipitation is usually small. The coldest part of the Northern Hemisphere is located in northeast Siberia near the city Verkhoyansk (Lydolph 1977), where present mean winter (DJF) air temperature is –43oC. Although frost may occur in any month, long summer days usually provide three months with mean temperatures above 10oC, and at some sites in the continental interiors summer temperatures may exceed 30oC. In such regions, forests extend 200-1000 km north of the southern limit of permafrost and, consequently, permafrost extends far beyond the traditional warm limit of periglacial environments (the tree line). Permafrost is widespread and typically reaches 300-600 m thickness.

In winter, arctic weather is dominated by the frequent occurrence of inversions where warm air overlies colder air near the terrain surface, decoupling surface winds from stronger upper layer winds. For this reason, surface wind speeds tend to be lower in winter than one might expect and cold (and dense) air tend to accumulate in topographic lows. In summer, inversions are less frequent and weaker, and the movement of low-pressure systems (cyclones) periodically dominate Arctic weather, even in central Siberia and in the Arctic Basin .

The Arctic is characterized by "semipermanent" patterns of high and low pressure (Serreze et al. 1993; Serreze et al. 1995; Serreze and Barry 1998). These patterns are semipermanent because they appear in charts of long-term average surface pressure. They can be considered to largely represent the statistical signature of where transitory high and low pressure systems that appear on synoptic charts tend to be most common. This pattern is relatively weakly developed in summer, but stronger in winter.

The Icelandic Low is such a semipermanent low-pressure centre located between Iceland and southern Greenland . It is most intense during winter, while in summer it weakens and frequently splits into two centres, one near Davis Strait and the other between Iceland and SE Greenland. Travelling cyclones formed in the subpolar latitudes in the North Atlantic usually slow down and reach maximum intensity when they pass the area of the Icelandic Low. The Aleutian Low is another semipermanent low-pressure centre, located near the Aleutian Islands in the Northern Pacific Ocean . Also most intense in winter, the Aleutian Low is characterized by many strong cyclones. Like the Icelandic Low, travelling cyclones tend to slow down and intensify while passing the Aleutian Low. Areas of significant winter cyclonic activity (storm tracks) are found in the North Pacific and North Atlantic. These channel heat, momentum and moisture into the Arctic, and significantly influences upon the high latitude climate.

Winter cyclones in the Eurasian Arctic occur most frequently in the Barents and Kara Seas region, bringing in pulses of warm air, causing rapid warming and snow melt even in the middle of winter. Over the North Atlantic Arctic, the highest frequency of cyclones occurs east of Greenland after having passed through the Icelandic Low. Cyclones are also common in Baffin Bay between Greenland and Canadian Arctic.

The summer distribution of air pressure and frequency of cyclones is different from that of winter. With more uniform temperatures over the northern parts of the Atlantic and Pacific oceans, summer cyclones tend to be weaker than their winter counterparts and the semipermanent Icelandic and Aleutian Lows weaken. In July and August, few strong cyclones move to the Arctic Ocean from the northern Atlantic , while several weak cyclones move towards the pole from the midlatitudes of Siberia and Canada .

 

Left diagram shows winter (DJF) sea-level pressure (SLP) averaged over the period 1900-2001. Isobars are spaced every 3 hPa with red colours used for SLP values greater or equal than 1013 hPa and blue colours used for lower values. Numbers at circumference indicate SLP values in hPa. Right diagram shows the modern distribution of permafrost in the Northern Hemisphere. Continuous permafrost is shown by dark blue colour. Discontinuous and sporadic permafrost is shown by light blue colour. Red and black arrows show main surface air flow (warm and cold, respectively) as generated by the 20th century pattern of SLP. The overall wind systems set up by the average winter sea-level pressure appears to represent one of several controls on the present distribution of permafrost in the northern hemisphere.

The Siberian High is an intense, cold anticyclone that forms over eastern Siberia in winter (see figure above). Prevailing from late November to early March, it is associated with frequent cold air outbreaks over East Asia. Strong cooling in this region results in the lowest air temperatures in the Northern Hemisphere. A persistent anticyclone or high-pressure ridge called the Arctic High, also known as the Beaufort High, is located over the Beaufort Sea and the Canadian Archipelago in winter and spring. The North American High is a relatively weak area of high pressure that covers most of North America during winter. This pressure system tends to be centred over the Yukon, but is not as well defined as its continental counterpart, the Siberian High. In the winter and spring, anticyclones in the Russian Arctic move mainly from the circumpolar regions through the eastern parts of the Barents and Kara seas. Some also move into the Barents Sea from the northern coast of Greenland . The sea level pressure distribution in summer is dominated by subtropical highs in the eastern Pacific and Atlantic oceans, with relatively weak pressure gradients in polar and subpolar regions. Arctic anticyclones are less common and generally weaker in summer.

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Unsolved climatological and meteorological issues in the Polar Regions

The meteorology of the Polar Regions is still poorly understood compared to other regions, and both better observational data and a more thorough analysis of existing data sets are needed to remedy this situation. In particular, the potential control exercised by local temperature inversions on registered Arctic surface air temperatures during the winter season should be investigated for individual meteorological stations. Many of these are located in or near settlements, which tend to be localised in topographic lows, in valleys, along rivers, etc. For such stations the frequent occurrence of winter temperature inversions during periods of calm causes them to be located in a shallow layer of very cold air, thereby recording extraordinary low temperatures not necessarily representative for the region as such. If the average number of calm conditions with temperature inversions during winter is reduced in periods with increased cyclonic activity, this will be recorded as a temperature increase, and vice versa. In summer, inversions are less frequent and weaker, and this potential source of error therefore smaller. New meteorological stations located at high altitudes will help solve this methodological problem (Christiansen and Mortensen, 2002).

The urban heat-island effect in the Arctic deserves separate scrutiny to improve the quality of existing meteorological records. At the village of Barrow, Alaska, Hinkel et al. (2003) recently demonstrated the existence of a strong urban heat island during winter. During winter the urban area averaged 2.2 °C warmer than the hinterland. The strength of the local heat effect increased as the wind velocity decreased, reaching an average value of 3.2°C under calm (<2 m/s) conditions and maximum single-day magnitude of no less than 6°C. Barrow has grown from a size of about 300 residents in 1900 to more than 4600 in 2000.

A central issue in Polar Region climate dynamics is to understand how climates in the Northern and Southern hemispheres are coupled. The strongest of the rapid temperature changes observed in Greenland (so-called Dansgaard-Oeschger events) during the last glaciation have an analogue in the temperature record from Antarctica (Blunier et al. 1998). A comparison of the global atmospheric concentration of methane as recorded in ice cores from Antarctica and Greenland permits a determination of the phase relationship (in leads or lags) of these temperature variations. Greenland warming events around 36 and 45 ka BP before present are lagging behind their Antarctic counterpart by more than 1 ka. On average, Antarctic climate change leads that of Greenland by 1±2.5 ka over the period 47±23 ka BP (Blunier et al. 1998). Also on shorter time scales, there appears to be an out-of-phase between climatic development in the Arctic and the Antarctic, such as demonstrated by the late 20th century cooling in the Antarctic and the contemporary warming in the Arctic (Ingólfsson et al. 2003).

 

Blizzard in Longyearbyen, Svalbard, 8 April 2003.

 

Another pressing meteorological issue is the distribution of precipitation in the Arctic, itself representing a complex problem, subject of long-standing debate and compounded by the paucity of meteorological stations. While air temperatures today are registered at Arctic meteorological stations with relative small technical difficulties, except for sites with icing conditions, precipitation is considerably more complicated to measure correctly, especially when in solid form. Many Arctic meteorological stations have simply avoided measuring precipitation due to severe problems by doing so. In addition, little is known about the local and regional effect of altitude and topography on precipitation. Also the local and regional importance of redistribution of snow by wind is usually virtually unknown (Humlum 1987; Humlum 2002; Humlum et al. 2003; Nordli and Kohler 2003). Finally, much of the information that does exist on precipitation within the Arctic tends to be widely scattered in the scientific literature and is often viewed only in the context of a particular local problem, with little emphasis on the regional amount of precipitation (Humlum 2002). In addition, high-latitude trends in measured precipitation are influenced by gauge undercatch. At a meteorological station exposed to warming, the fraction of annual precipitation falling as snow diminishes, and vice versa. As the gauge undercatch is substantially larger for solid than for liquid precipitation, this implies that a fraction of any observed positive precipitation trend is fictitious, caused by reduced undercatch in the precipitation gauges (Førland and Hanssen-Bauer 2000). For these reasons, we have shunned from discussing precipitation in this contribution.

The general problem of reliable records on Arctic precipitation, however, remains, and also has implications for knowledge on duration and thickness of the snow cover, significant for the ground thermal regime (Ballantyne 1978; Humlum et al. 2003). Snow plays a key role in protecting plants and animals from cold dry winter conditions. It is also important for the seasonal water cycle. Variations in the snow cover may therefore have profound impact on biological activity and geomorphic activity in the Arctic. In addition, the snow cover also has a direct effect on the distribution of permafrost on both local and regional scale (Humlum et al. 2003). In arid parts of the Arctic land regions the average winter snow cover is thin and the ground surface cools rapidly during the winter. Conversely, in more maritime areas the snow cover usually is thicker and reduces heat loss from the ground surface during winter. Interannual variations in the establishment of the snow cover are also important. A dry and cold autumn enables enhanced cooling of the active layer and topmost permafrost, while high snowfall during late winter and late onset of snow melt protect the ground against thawing in early summer. The combination of these two meteorological phenomena is likely to be beneficial for conservation and growth of permafrost. Variations in the timing and duration of seasonal snow cover presumably also have an influence on active layer thickness, but the effect is still not known in detail (Humlum et al. 2003).

A specific problem adheres to the lack of knowledge on mountain climate in general. Despite the fact that high-relief areas (mountains) account for about 20 per cent of the earth’s land surface, the meteorology of most mountains is still little known. Meteorological stations are few and tend to be located at conveniently accessible sites, often in valleys or along coasts, rather than at points selected to obtain representative data. Precipitation distribution in mountain areas has been a subject of debate and controversy since the publication on orographic rainfall by Bonacina (1945). The problem is compounded by the above-mentioned paucity of high-altitude meteorological stations and the additional technical difficulties of determining snowfall contributions to total precipitation, especially at windy sites. As recognized early by Salter (1918) from analysis of British data, the effect of altitude on the vertical distribution of precipitation in mountain areas is highly variable between even nearby geographical locations.

This poor understanding of the dynamics and characteristics of mountain climate is particularly pronounced for the Arctic (Humlum 2002). This is unfortunate; partly because of existing predictions of an amplified response of northern high-latitude regions to various climatic forcing mechanisms (see above), partly because most geomorphic activity is not controlled by temperature only, but very much also by precipitation and wind, e.g. frost weathering, gelifluction, active layer processes (e.g., Etzelmüller and Sollid 1991) and the dynamics of glaciers (e.g., Dowdeswell et al. 1997). Also any kind of biological activity is likely to be influenced by the amount of precipitation.

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Click here to see decadal variations of precipitation and surface air temperature in the northern hemisphere polar region during the 20th century.

Click here to see a spatial analysis of monthly variations of surface air temperature in areas between 72oN and 60oS since 2005.

Click here for an update on present global, Arctic or Antarctic meteorological conditions.