How do ocean currents affect coastal climate?

Ocean currents usually flow from the poles or the tropics. Water flowing from the tropics flows to the poles and regulates the temperature when the cold and warm water collide, making sure the climate at the poles does not get too cold. It does this because when water is warm, it swells, stretching out to other colder climates. When the water becomes cold, the water contracts to the warmer regions. But there are exceptions, such as El Nino. This is caused when the Pacific current shifts, changing direction.