Quotation marks, also called 'inverted commas', are of two types: single and double. British practice is normally to enclose quoted matter between single quotation marks, and to use double quotation marks for a quotation within a quotation:
The oceans absorb the sun's heat, transferring it to the atmosphere and distributing it around the world via the ever-moving ocean currents. This drives global weather patterns and acts as a heater in the winter and an air conditioner in the summer.
> Ocean currents transport enormous amounts of heat around the world. This makes them one of the most important driving forces of climate. Because they respond extremely slowly to changes, the effects of global warming will gradually become noticeable but over a period of centuries.