The best example of this is in the North Atlantic, where the Gulf Stream brings rain and warm weather to western Europe and the salt returns south at depth. If this conveyor belt is disrupted, it can trigger an ice age.Ocean currents depend on the positions of the continents, and continental drift has caused major climatic change in the past.
About 30 million years ago an eastward circumpolar current established itself around Antarctica, isolating the continent from other weather systems and leading to the development of the ice cap. A modern example of the effects of changing currents is El Nino (means The Child, so called because it occurs at Christmas) a warm current that can develop in the pacific and move towards the coast of Peru. It causes disruption to fisheries and triggers equatorial drought and tropical storms.