Normally, the current is driven by the cooling of water as it travels to the northern part of the Atlantic. As water cools, it becomes denser and sinks. This pulls warm water from the south to replace it. But with climate change, melting glaciers and Arctic sea ice are overwhelming the system with fresh water, which is less dense and therefore less heavy than salt water, so less water sinks and less warm water is drawn from the south, disrupting the entire system.