This is a lovely video of the Arctic sea ice disappearing. The age of the ice is especially important. Watch the white and you can see it disappearing. The oldest ice is, generally, the thickest.
Notice as well the darkest part. That is ice, so you can’t go through it with an ordinary boat, but it too, is diminishing.
Global warming deniers are fond of pointing to an increase in ice extent in part of Antarctica. The increase in ice is of the type that is darkest here. Since it is new, it is not thick and will melt quickly as the Earth continues to warm.
The reduction of ice changes the patterns of the wind and thus, the patterns of currents. The difference between hot and cold is a large factor in what causes winds. As the poles warm, there is less difference and the important winds and currents that create our current weather pattern are changing. When the global weather patterns change on a global basis, the climate has changed. This is one way that global warming causes climate change.