71% of the earth is covered by water of which 6% is ice. Therefore absorption of solar energy and evapo-transpiration of water at the earth’s surface are dominated by the oceans. These drive the earth’s climate system. Heat is transferred frim the equator towards the poles by the atmosphere and the ocean. The atmosphere does this by eddies in the middle and high latitudes. The ocean does this by boundary currents, vertical overturning and wind-driven gyres.
In Oceanography a gyre is a ringlike system of ocean currents rotating clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.
We are at present, nearest to the sun in January. The southern hemisphere receives more sunlight than the northern hemisphere. But the northern hemisphere contains the thermal equator.
In Physical Geography, the thermal equator is an imaginary line round the earth running through the point on each meridian with the highest average temperature. It lies mainly to the north because of the larger landmasses and therefore greater summer heating. In the Atlantic Ocean this is because of South America and Africa. The Atlantic transports 10**15 W of heat across the equator into the northern hemisphere.
The climate system reacts strongly and rapidly to minor changes. Human caused global warming is often referred to as anthropogenic climate change. Oceans are the major sink for the carbon dioxide generated by humans. Oceans clearly affect regional climates with their heat absorption and transport mechanisms. When they absorb heat they expand, melt the ice caps, increase in volume resulting in sea level rise, coastal erosion and flooding. It is hard to quantify how much damage humans are doing and whether it is significant. Ocean observations are harder than atmosphere observation because the oceans are opaque to electromagnetic radiation. Reference: 1. Ocean circulation and Climate: Siedler, Church, Gould. Chapter 1.1 The featured image is from: http://ancientindians.wordpress.com/2012/08/23/fishing-harbour-visakhapatnam/