Possible events:
1492 The asteroid falls in Antarctica melting part of the Ice cap and sending debris to the Atmosphere that cause a Greenhouse effect.
During the first year sea levels increase something around three-five meters due to the consequences of the impact. From there on it raises at more or less one meter per year. So we could have the 100m level by the 1600s.
The Gulf Stream is interrupted making the temperatures in Europe to lower. They would be a bit warmer than OTL Canada (a bit warmer because of the GH effect).
Weather becomes globally warmer and wetter, except in Europe that is colder and wetter.
So the situation around 1600 could be something like:
* Scandinavia. Lower temperatures make the region unable to support big concentrations of population. Central Power collapses both in Sweden and Denmark. The Danes first flee to Sweden and Norway. As temperatures lower they migrate to the new coasts of Germany and probably some groups reach the Mediterranean. The Norwegians could remember the Auld alliance and flee to France. Some could migrate to Iceland, when the island becomes inhabitable, they owuld move with the Icelanders to Greenland.
* British Islands. The sea covers most of England and Ireland making the population flee very soon to the south. The English would go to France and Spain and the Irish to Spain. Scotland could consolidate as a temporary regional power taking what is left of England. Wales could become independent. As temperatures lower, the Scotch would migrate south to France (Auld alliance).
* Iberian Peninsula. Spain would be quite untouched by the sea level increase, except for some coastal regions. Portugal would be more dramatically affected as they would lose their main cities. Spain would absorbe Portugal and they would redirect the new population contingents from the British Islands and the rest of Europe for the continuation of the Reconquista in North Africa. Changes in the Atlantic currents and climatology would hinder colonization of America and would make them to redirect efforts to the Mediterranean and the North of Africa looking for milder lands.
* France. Possible collapse due to loss of lands and migrations. The arrival of Walons, Scotch and Norwegians could re-strenghten them and become again a power or be torn by religious conflicts between alt-calvinists, catholics and other religious groups that might arise. Savoy could prosper by taking some lower lands to France.
* Italy. Genoese and Venetians would be utterly destroyed. The Venetians would be the first to disappear and they would probably migrate first to the interior of Northern Italy and some would move to their possesions in the Eastern Mediterranean (Morea, Crete, Cyclades and Cyprus). The Genoese scatter along the western Mediterranean and they would stick to Corsica. Milan would be invaded by the Suiss looking for milder lands. The rest of Italy would be untouched. Naples would probably preserve its independence from France and Spain, although associated to the first due to dinastic bonds.
* Central Europe. The presence of refugees from the Netherlands, Flanders, Denmark, Northern Germany and Sweden plus the presence of religious groups like Hussites, alt-Lutherans and others would turn the region into a very conflictive one. The Habsbugh would probably carve the most powerful state and eventually reach an agreement with all the sides.
* Eastern Europe. Possible survival of the Teutonic Order in their new insular (although extremely cold) territories. Conflict between Lithuania and Russia for the control of the Region. The Ottomans could use the new Danubian channel as support for their invasion of Hungary and the rest of the Balkans. They could be more oriented to the Black Sea and the new channel to the Caspian and Less to the Mediterranean.
* Middle East. Egypt could be free from the Ottomans but more pressed by the Spanish, Venetians and other powers. Syria, Palestine and the Caucasus would be in ottoman hands. The Persians could project to Central Asia and the new trade routes.
* Asia. Collapse of Chinese power. Inundation of Ghanges valley prevents the Moghul Empire to appear.
* Africa. More Atlantic oriented Songhai. The spanish kings control the Maghreb and colonise it with northeuropeans.
* America. The spanish colonies barely survive. More commercial policy. Aztec empire manages to adapt to Europeans and survive, they could expand to the north. The Incans also have time to adapt and survive. Possible clash in Mesoamerica between Mayans, Incans and Aztecs. In Terranova small groups of Irish, English and Scottish could arrive and create mestizo societies.
What do you think of this?