Which effect can a ocean have on a climate?

The oceans make the climate milder in general, but they can make a place very wet or very dry.

Explanation:

The oceans are one of the major climate modifiers. They contain a huge amount of water in them, and with the water having different properties than the land it manages to alter the climate along the coastlines or in the islands. The water, unlike the land, is heating up and cooling off much slower, thus its temperature is much more stable, making the areas under its influence much milder.

On the other hand, there is a big difference in climatic influence between warm ocean water and cold ocean waters. The first ones create warm and wet air masses above them so when they make the areas they influence pretty wet. The cold ocean waters create cold and dry air masses, and these air masses don't bring in precipitation on the land, so they create arid and semi-arid climate conditions.

the one feature that all mediterranean countries have in common is that they border the mediterranean sea.

explanation: