I think it is a bit hard to implement when several years are one turn and so on... but here we go:
Think of icebergs floating in the northern parts of the map, vanishing in warmer regions.
Curraghs sunken by icebergs...
Sea storms, speeding up ship movement and driving them to different shores. Land bridges of ice that allow crossing by foot.
Grasslands turning to desert and much more.
A more dynamic worldmap in general, weather having effect on production, food and such things.
I think this would enrich the worldmap and allow new strategic options.
Think of icebergs floating in the northern parts of the map, vanishing in warmer regions.
Curraghs sunken by icebergs...

Sea storms, speeding up ship movement and driving them to different shores. Land bridges of ice that allow crossing by foot.
Grasslands turning to desert and much more.
A more dynamic worldmap in general, weather having effect on production, food and such things.
I think this would enrich the worldmap and allow new strategic options.