Fresh water has a different density than salt water, and ice melting in the artic and antarctica is resulting in a huge influx of fresh water that can disrupt ocean currents [2]. These currents currently distribute a lot of heat around the world, and them stopping would result in places like europe getting much colder, while other regions would become much hotter (and with the warmer oceans, probably also have extremer hurricanes).
[1] https://www.nationalgeographic.org/media/earths-fresh-water/
[2] https://wikipedia.org/wiki/Shutdown_of_thermohaline_circulat...