In 10th and 11th century there was wine commonly produced in Poland and instead of Hel there were 3 islands, on the other hand in 17th century the whole Baltic used to freeze in the winter.
There is a scientific explanation to this anomaly, my wife is finishing her PhD at the National Institute for Soil Science here in Pulawy, and she was telling me that there is strong evidence to suggest that man has had an indirect affect on the climate in Europe even as far back as the 14th century.
In the 1340s the Black Death had spread to Europe and is said to have wiped out over a third of Europe's population, this caused a drastic drop in agriculture and a massive rise in forestation in Europe.
This rise in forestation had a massive impact because millions of trees sprang up on abandoned farmland, soaking up carbon dioxide from the atmosphere, and researchers at my wife's institute think that this drop in carbon dioxide levels could help to explain a cooling in the climate over the following centuries.
This in turn would have had a massive effect of cooling the climate.
Before this time as Grzegorz says Europe had a period that was relatively warm, but after the 14th century this warm period was replaced by the so-called "little ice age".
This would explain the freezing of the Baltic and the pictures of the freezing of the River Thames where they would hold markets on the ice in the winter.
And I may add that all the scientist that I have spoken to from this institute totally agree that man’s impact is having a direct influence on the world’s climate.
Furthermore, most of these so-called facts disproving global warming have been put out by the US and other countries that do not want to fork out billions in redeveloping their industries to be cleaner.