Surface currents are movements of water at or near the surface. Global winds are like you blowing on a cup of hot chocolate. The only difference is the current is a lot smaller in the cup of hot chocolate. The wind on the earth has the power to move massive amounts of water. The Coriolis effect is the turning of any object on earth by its rotation, so it causes winds to go in curved paths. When surface currents meet land they go in a different direction. All three of these things work together to form a pattern of surface currents. Type of currents are effected by the temperature of the water too. Warm water currents start by the equator and cold water currents start by the poles.
Deep currents are like surface currents accept they are far below the oceans surface. They form areas where water density increases. The way they move along the ocean floor is very complex. Differences in temperature, slope, in density cause differences in deep current. Surface currents and deep currents trade places with each other like air.
Surface currents effect the climate greatly in many parts of the word. They cause changes in the atmosphere that mess up the climates in many parts of the world. Because surface currents can be cold or warm they effect the climate near where they flow. When surface currents in the tropical region of the pacific ocean travel with the trade winds it builds up warm water it causes in upwelling in the eastern pacific. Upwelling is a near shore process that cold water from deep currents rise and replace warm water from the surface currents. El Nino is the change in warm and cool surface water in the Pacific. It also changes the interaction between the ocean and the atmosphere. These changes are a result of El Nino.
The scientists are concerned about the climate changes caused by El Nino because they can cause major disasters. During this season the rain is over the middle of the pacific and completely misses southeast Asia. In places where it rains a lot, they will experience droughts and that can lead to crop failures and where there is very little rain, they will experience mudslides.