Climate Change in Baltic Sea Area
Baltic Sea – background informationBaltic Sea is a relatively shallow sea in north-eastern Europe, surrounded by the Scandinavian Peninsula, the mainland of central and east Europe and the Danish islands. It is connected with North Sea through Kattegatt, Øresund, the Great Belt and the Little Belt. It covers area of about 415 000 km2 and its average depth is 55 m. The central part of the Baltic Sea is known as Baltic Proper, other large parts which might be distinguished are the Bothnian Bay, the Bothnian Sea, the Gulf of Finland, the Gulf of Riga, and the Gulf of Gdansk, the Bornholm and Arkona basins, followed by the Sound, the Belt Sea and the Kattegat.
The Baltic Sea is surrounded by nine countries: Denmark, Sweden, Finland, Russia, Estonia, Latvia, Lithuania, Poland and Germany.
Baltic Sea Area
The Baltic Climate: Past Climate and Recent Climate Change
Two major climate types dominate in much of the Baltic Sea Area:
- most of middle and northern areas are determined by the temperate coniferous-mixed forest zone with long, cold, wet winters, where mean temperatures of warmest month is no lower than 10°C and that of the coldest month is no higher than −3°C, and where the rainfall is, on average, moderate in all seasons;
- much of the southwestern and southern areas belong to the marine west-coast climate, where prevailing winds constantly bring in moisture from the oceans and the presence of a warm ocean current provides for moist and mild winters, with frequent thawing periods even in mid-winter.
Temperature and the warming trend over the Baltic Sea Region
The annual warming trend for the Baltic Sea basin has been shown to be 0.08°C/decade. What is higher than the worldwide trend which is about 0.05°C/decade. This warming trend can be observed as a decrease in the number of very cold days during winter as well as a decrease in the duration of the ice cover and its thickness in many rivers and lakes, particularly in the eastern and southeastern Baltic Sea basin. Furthermore, an increasing length of the growing season in the Baltic Sea basin has been observed during this period.
In the 20th century, temperatures in the Baltic Sea basin increased during the early part of the century (termed the early 20th century warming) until the 1930s; then there was a cooling period till 1960s, followed by another warming which has continues till presence (Figure 3).
Warming is characterized by a pattern where mean daily minimum temperatures have increased more than mean daily maximum temperatures. In spring the most linear and strongest warming was observed whereas wintertime temperature increase is irregular but larger than in summer and autumn.
The climate warming is reflected also in time series data on the maximum annual extent of sea ice and the length of the ice season in the Baltic Sea. Regarding the ice extent, the shift towards a warmer climate took place in the second half of the 19th century. The length of the ice season showed a decreasing trend by 14–44 days during the 20th century, the exact number depending on the location around the Baltic Sea.
Recent observations have provided an estimate (for the past 30 years) of mean annual precipitation of 750 mm/year for the entire Baltic Sea basin, including both land and sea. The highest precipitation occur in the mountain regions in Scandinavia and southern Poland, while the lowest amounts of precipitation occur in the northern and northeastern part of the basin as well as over the central Baltic Sea. Increase in precipitation has been observed however there is no uniform spatial distribution of this increase. Within the Baltic Sea basin the largest increases have occurred in Sweden and eastern coast of the Baltic Sea. Seasonally largest increases have occurred in winter and spring. Changes in summer are characterized with increases in the northern and decreases in the southern parts of the Baltic Sea basin. Seasonally, winters are projected to become wetter in most of the Baltic Sea basin and summers to become drier in southern areas for many scenarios. Northern areas could generally expect winter precipitation increases of about 25% to 75%, while the projected summer changes lie between 5% and 35%. Southern areas could expect increases ranging from about 20% to 70% during winter, while summer changes would be negative, showing decreases of as much as 45%. Taken together, these changes lead to a projected increase in annual precipitation for the entire basin.
Climate induced Changes in Baltic Sea Area Ecosystems
The external water budget of the Baltic Sea is dominated by water import from river discharge, exchange with North Sea water, and net precipitation (precipitation minus evaporation). Water inflow from North Sea is very restricted and only Kattegat deep water contributes to the Baltic Sea water renewal. Taking into account freshwater supply the estimated residence time of water in Baltic Sea is about 33 years. A lowering of salinity (due to generally higher precipitation and river discharge) is thought to have a major influence on the distribution, growth and reproduction of the Baltic Sea fauna. Freshwater species are expected to enlarge their significance, and invaders from warmer seas (such as the zebra mussel Dreissena polymorpha or the North American jelly comb Mnemiopsis leidyi) are expected to enlarge their distribution area. Climate-induced changes in marine ecosystems would include changes in nutrient cycling and contaminant distribution and changes at all trophic levels from bacteria to seabirds and marine mammals.
Management Strategies towards Climate Change in the Baltic Sea Region
The Baltic Sea Region faces variety of challenges due to recently observed climate changes, mainly general trend for increasing temperature and changes in precipitation pattern. Different methods are requested to deal with problems on regional and local scales. Some of most important issues which require management strategies are:
- needed level of coastal protection;
- severe flooding events prediction and appropriate mitigation aftermath;
- water shortage.
The concepts of adaptation and mitigation related to climate change are presented in figure 4. Adaptation activities help to diminished the negative climate change impacts or exploit beneficial opportunities of climate change. Mitigation activities are devoted to strategies and measures for green house gases emission reduction.
Management strategies towards climate change impacts are rarely implemented in policies of the Baltic Sea Region countries. Analysis of current and future risks is needed for development of adequate adaptation solutions. However, adaptation and mitigation approaches should not be regarded as a separate topic. They are be to integrated in different fields of policies on regional, local, national and international level.
- Climate Change in the Baltic Sea Area – HELCOM Thematic Assessment in 2007 Baltic Sea Environment Proceedings No. 111, HELCOM, 2007.
- BALTEX Assessment of Climate Change for the Baltic Sea Basin, Göteborg 2006.
- Hilpert, K., Mannke, F., Schmidt-Thomé, P. (2007): Towards Climate Change Adaptation in the Baltic Sea Region, Geological Survey of Finland, Espoo.
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