Baltic Navigation in Ice in the Twenty First Century
Wybrane pełne teksty z tego czasopisma
The Baltic Sea, even though not large in the global scale, is an important shipping lane. In winter, especially in the region of the Gulf of Bothnia, navigation is seriously obstructed by ice. The aim of this work was investigation of changes in the intensity of the obstruction by ice, caused by climate change in coming 90 years of the twenty first century. It was one of the first attempts of technical application of the global climate scenarios effects. It should be stressed, that the presented work results (as application of the climate scenarios), couldn’t be treated as forecast, as it is only the changes tendency assessment. The climate changes were examined as the changes in air temperature (adaptation of global emission models to regional scale) and atmospheric pressure gradient (model ECHAM5), according to three global scenarios B, A2 and A1B. The number of cases, in which Swedish and Finnish icebreakers assisted the ships, was assumed as the indicator of navigation obstruction by ice “K”. The severity of sea ice conditions was presented by the indicator “S”, calculated as the mean value of regional indices. The “S” is the function of the number of days with sea ice, observed at the stations in the particular regions and probability of the sea ice appearances. Relations between sea ice severity index “S” and regional climate parameters (monthly and annual air temperature and atmospheric pressure gradient ) were calculated for the calibration period of 1956-2004. Three models were build: model 1a. “thermal” (the dependence on the mean monthly temperature of July and December); model 1b. thermal “B” (the function of average annual air temperature and of the mean monthly December temperature) and model 2 “thermal zonal” (the dependence on the mean temperature of July and December and zonal component of air pressure gradient). The level of approximation was similar for the analyzed models (over 0,6). Calculation of the future (in XXI century) changes of indicator “K” was done according to three scenarios B, A1B and A2. The number of icebreakers’ assistance events should be lower than the one in the twentieth century. The lowest intensity of this decrease is estimated by model 2 and scenario A1Br1, the highest one – for model M1b and scenario B r1. Otherwise, the minimum value, calculated for the scenarios, is higher than in a period of 1956-2004. It means, that probably, the period with obstruction for navigation in ice could be longer, but not as severe as in the period of 1956-2004. The obstruction intensity could increase during the 21 century according to scenario B1r1, the same for empirical model 2. The similar tendency has been shown by scenario A1Br1 and by model 1a. Other models and scenarios estimated the decreasing trend up to 2100.
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