Oh, you can't ice skate on the Baltic Sea. There's no flat surface, just small patches of ice. You mustn't go out on them, it's far too dangerous. Just last weekend, a man and his 5-year-old (!) son had to be rescued. How stupid can you be???
Even if a large area were frozen over, it wouldn't be smooth because of the waves. Not suitable for ice skating.

But skating (or even just walking) on a large lake is an amazing experience. When the thick ice cracks, the sound waves in the deep lake turn into a dull rumbling. Very impressive! And a little eerie...

How do human survive this period...?

Haha, you should ask the Inuit at the North Pole. You can protect yourself from the cold with good clothing and furs (sheep show us how).
I tend to ask myself this question in certain parts of Africa. What else can you take off in the heat? What can you drink? Here, you can always melt snow if necessary.
No, no, better too cold than too hot... 😇