Oceans and climate
The upper few metres of the ocean contain the same amount of heat as the entire atmosphere. The oceans therefore act as a giant heat reservoir and significant changes in the amount they store can only occur over hundreds of years. Ocean currents also transport heat within and between the major ocean basins. Thus, oceans moderate climatic changes as well as playing an important role in driving climate change. Our oceans are warming and hence expanding in volume, and this is contributing to the observed increase in global mean sea level of about 3mm per year.
