Since more than 100 years, winters in the Baltic Sea have been classified according to their strength and have been compared to each other. In the beginning, the winter strength was only related to the ice coverage along the coasts. However, since the 1980s, also the ice thickness was observed consistently and has therefore been included into the classification scheme. Owing to the international cooperation between the European ice services, we have all the needed information about the winter strength, sea ice coverage, distribution and mass for the entire Baltic Sea available. Thus, we have been able to compute changes in the sea ice conditions for this area covering the last decades and to compare them with changes in the air and sea surface temperatures. For the first time, we show the distribution of the mean accumulated sea ice concentration and sea ice volume as well as its trends for the Baltic Sea. Consistently data reveal a decreasing amount of sea ice that is produced over a winter season for nearly all the sections of the Baltic Sea. The reduced sea ice production correlates generally well with the increase in air and sea surface temperatures over winter months.

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1982年至2019年的30年期间，波罗的海海冰量的区域分布趋势

100多年来，波罗的海的冬季已经根据强度进行了分类，并进行了比较。最初，冬季的强度仅与沿海地区的冰覆盖有关。但是，自1980年代以来，也一直观察到冰的厚度，因此已将其包括在分类方案中。由于欧洲冰服务之间的国际合作，我们获得了有关整个波罗的海的冬季强度，海冰覆盖范围，分布和质量的所有必要信息。因此，我们已经能够计算出该区域过去几十年的海冰状况变化，并将其与空气和海面温度的变化进行比较。首次，我们显示了平均累积海冰浓度和海冰量的分布及其在波罗的海的趋势。一致的数据显示，在冬季，波罗的海几乎所有地区的海冰数量都在减少。减少的海冰产量通常与冬季几个月中空气和海面温度的升高高度相关。