Zhaden, Oleg (2011) The Melting of the Antarctic Ice Cover and Assessing Its Change Over the Past Millennium Using Climate Models. (Master thesis), State University of St. Petersburg, Russia ; University of Hamburg, St. Petersburg, Russia ; Hamburg, 49 pp.

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Abstract

This work covers the assessment of melting trends of the Antarctic ice cover over the last millennium.
BACKGROUND
Recent evidence of dramatic climate change has prompted well grounded – and not purely academic - interest in probable consequences of this phenomenon. Global climate change inevitably entails major changes for all living beings on the Earth including human population.
One of the most important and potentially harmful consequences in thought to be raising of the World Ocean level which will happen if global ice cover melts down.
Because the Antarctica and Greenland account for more than 90% of the world's ice melting of these two ice caps makes a major contribution to global ocean level increase. If the Antarctic and Greenland ice caps melted down completely global ocean level would increase by 70 meters – a serious threat to those who live in the coastal areas, which is about half of the global population. Even melting of just a fraction of the ice cover and resulting increase by a few meters is serious enough. So the state and dynamics of the Antarctic and Greenland ice caps is the subject of intense concern of scientists and environmentalists worldwide.
It is also necessary to take into consideration that the glacier melting is not the only process which may lead to sea level rise. The melting itself is a quite gradual process, we could not imagine the climatic conditions by which a huge amount of ice will be able to melt immediately. At least, by the current conditions such a development of the situation seems to be an unlikely event. However, there is a probability of other process which potentially more dangerous and less predictable in terms of velocity of sea level rise - the acceleration of glacier flow and input of ice into the ocean.
As compared with a melting of glaciers, the danger of such an ice movement is that for this is just enough a thaw of ice-bed contact and therefore it might occur on a much earlier stage of the melting. We know that the glacier grip with the underlying bed is one of the most important factors which have an influence on the velocity of glaciers. Also we need to take into account that lowest layers of glacier usually have temperatures near the melting point due to Earth's radiation, high pressure and friction. Therefore, even a comparatively small changes in a temperature balance towards its growth may lead to considerable acceleration of the glacier movement and ice discharge into the ocean. Its well known that approximately 90% of ice of the Antarctic ice sheet moves into the ocean via the ice streams, which feed the ice shelves, from which due to calving ice goes directly into the water. In a stable climatic conditions this process is balanced by the snow accumulation inland of Antarctica but in case of global warming the ice discharge into the ocean exceeds the accumulation that leads to sea level rise.
RESEARCH METHODS
The objective of the research is the estimation of trends of the Antarctic ice cap melting in the last thousand years. Because of the obvious reasons (unavailability of recorded data) we have to use a climatic model. The research is based on the calculation of PDD (Positive Degree Days) – a value that represents the number of days during the year with positive temperatures T > 0°C. However, by definition PDD is not literally the number of days with average positive temperatures but rather a sum of positive temperatures divided by the number of days when these positive temperatures were recorded. In some cases when melting period is long and average temperatures are high enough the value of PDD for the year may be more than 365; for example, if the number of days with average positive temperature is 100 and the average temperature for this period is +4°С, the total value of PDD would be 400.
RESULTS
Values of PDD for every year from 800 until 2005 were calculated. To access the reliability of the results the modeled values of temperature were compared with the available meteorological data from the British meteorological station Faraday (from 1996 – Ukrainian station Vernadsky) because this station has the longest temperature record (from 1940-s). We used the period 1950 – 2005. The correlation between the observed data and modeled valued is estimated. The plot depicting the trend of PDD from 1950 to 2005 is obtained.

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