Antarctic temperature changes during the observational period

 

A project funded by the University Courses on Svalbard (UNIS) 2001-2005

Ole Humlum, UNIS, Department of Geology, Svalbard, Norway

 

Background

The Polar Regions have gained a prominent role in the scientific debate regarding global climatic change. Existing knowledge on Quaternary climate and Global Climate Models (GCMs) both predict that the effect of any present 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.

Considering an enhanced greenhouse effect, all GCMs indicate that the Polar Regions should experience a much larger warming than would occur in lower latitudes due to two basic 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 emission from ice and snow. Secondly, water vapor, sharing overlapping absorption bands with CO2, is only present in limited amounts in the polar atmosphere due to low temperatures, allowing CO2 to exert a much greater influence than would be possible in warmer and moister air masses at lower latitudes. An important enhanced greenhouse signal would thus be strong warming in the polar and sub-polar regions and less warming at lower latitudes.

 

Data source and analysis

In the present project maps showing the spatially interpolated Antarctic surface air temperature variations are produced in order to provide insight into the overall geographical pattern of late 20th century Antarctic surface temperature changes. As new data become available, updated maps showing recent changes will be produced and published on this site. 

Most of the homogenized Antarctic meteorological data used in the analysis were obtained from the NASA Goddard Institute (NASA 2002; data accessible by web). 

Antarctic and Arctic temperature records are characterized by a very high level of interannual variability. Therefore, although recognizing the importance of such interannual variations, it was decided to reduce the influence of such short-term variations and to highlight trends by analyzing 5-year unweighted running temperature means centered on 1960, 1970, 1980, 1990 and 1998, respectively, using data from 1958 to 2000. The observed temperature changes were then interpolated spatially across the entire Antarctic continent, using a kriging algorithm. Kriging is considered one of the more flexible interpolation methods, producing a rather smooth map with few ‘bull eyes’ and is usually recommended for gridding almost any type of data set.

 

Results

The results of the spatial surface temperature analysis are displayed in the accompanying map series (Fig.1; below), showing both annual and seasonal changes from 1960 to 1998, in 10-year steps. Also existing meteorological data from islands in the South Atlantic and South Pacific were incorporated into the analysis, although the temperature maps are truncated shortly beyond the Antarctic coast. Ship based temperature observations were not included in the present analysis due to potential difficulties with such data.

 

Fig.1.  Map series showing Antarctic surface air temperature changes 1960-1998, based on 5-year unweighted running temperature means centered on 1960, 1970, 1980, 1990 and 1998, respectively, using data from 1958 to 2000. Curve interval: 0.2oC. Red colors indicate rising temperatures and blue indicate decreasing temperatures. From left to right: summer (DJF), autumn (MAM), winter (JJA) and spring (SON). 

 

Compared to other seasons, the summer season (DJF) only has experienced small changes. The first period 1960-1970 was a time of slight summer warming throughout most of Antarctic, followed by a period of gradual cooling. The net result for the whole period 1960-1998 has been slight summer cooling in the Antarctic mainland and more pronounced warming in the Antarctic Peninsula.

Autumn (MAM), winter (JJA) and spring (SON) has all been characterized by larger variations. Except for the Antarctic Peninsula, there has been a general trend towards cooler autumn conditions throughout the observational period, especially affecting East Antarctic. The net result for autumn has been warming in the Antarctic Peninsula and cooling of the Antarctic mainland.

The temperature changes during the winter period (JJA) have been more complicated and shifting regions of warming and cooling has affected different parts of the continent during the observation period. Any warming has been most pronounced in coastal regions and less so in the interior. The net result 1960-1998 has been winter warming in the coastal regions, including the Antarctic Peninsula and little change in a central region extending from Vostok towards Halley Base at the Weddel Sea.

Spring (SON) has also been characterized by shifting regions of warming and cooling, in some respects resembling variations during the winter season. Warming dominated during the periods 1960-1970 and 1980-1990, while cooling took place in the intervening periods. The net result from 1960 to 1998 has been spring warming in East Antarctic coastal regions between Ross Sea and Mawson Station, while the interior regions and the Antarctic Peninsula has cooled.

These seasonal changes have affected the mean annual air temperature (MAAT) in various ways, although the net continental surface temperature change has been small for the full period 1960-1998. There have been some warming affecting mainly coastal regions between the Ross Sea to the Antarctic Peninsula, while net cooling has affecting the interior areas and most of the East Antarctic Plateau. Figure 2 (below) exemplifies some temperature series from various sites in the Antarctic continent.  

 

Fig.2.  Diagram showing examples of surface air temperatures from Antarctic stations. The mean annual air temperature is indicated with a dot and the solid line represents the 5-year unweighted running mean. Stations within the Antarctic Peninsula region (Orcadas and Esperanza) show a late 20th century warming, while stations on the East Antarctic Plateau (Amundsen-Scott and Vostok) show cooling.

 

Summing up

The existing Antarctic surface air temperature records 1960-1998 reveal periods of persistent (multi-year) and geographically extensive temperature trends towards cooling in the interior and warming in the coastal regions. The spatial and seasonal patterns of these trends are, however, not quite simple and appear to change with time; that is, the temperature relationship between specific locations is not temporally consistent. Within the Antarctic Peninsula a warming trend has, however, persisted, with exception of the spring season. The cooling has been modest in coastal East Antarctic regions, but more pronounced at the Amundsen-Scott Base and at the South Pole. By this, a Peninsula-East Antarctica Plateau temperature opposition apparently has prevailed during much of the late 20th century. 

The observed temperature changes since 1957 has been difficult to simulate by GCMs (Connolley and O’Farrell 1998) and is not yet fully understood. The observed spatial pattern of temperature variations may, however, indicate that the consecutive warming and cooling throughout the decades was part of a large-scale circulation pattern that exhibits long-term persistence. Mean winter surface temperature trends in Antarctica have previously been linked to slow (multi-year) variations in atmospheric long waves (van Loon and Williams 1977), suggesting that mid-latitude large-scale circulation plays a significant role in the spatial variability of temperature over the continent. There is some observational evidence suggesting that under present conditions cooler conditions on the Antarctic Plateau are associated with stronger zonal westerlies around the Antarctic continent, causing warmer conditions in the Peninsula regions penetrating north into the zone of enhanced westerlies.  

 

Update 2002

Meteorological data from 2002 are now available, which makes it possible to take a more detailed look on changes in 5-yr running mean 1990-2000, using data 1988-2002. Maps showing seasonal and annual air temperature change are found below.

References

Connolley, W.M. and O’Farrell, S.P. 1998.  Comparison of warming trends over the last century around Antarctica from three coupled models. Annals Glaciology 27, 565-570.

Van Loon, H. and Williams, J. 1977.  The connection between trends of mean temperature and circulation at the surface: Part IV. Comparison of the surface changes in the Northern Hemisphere with the upper air and with the Antarctic in winter. Monthly Weather Review, 105, 636-647.

 

Relevant LINKS

Below you will find some links to web sites with further information about the Antarctic:

Antarctic weather now

Antarctic sea ice now

British Antarctic Survey

Hamilton workshop on Antarctic Peninsula Climate Variability (April 2-5, 2002; poster)

Antarctic paper in Polarfronten (printed version)

Antarctic paper in Polarfronten (web-version)

 

 

Latest update: 5. April 2005.