Lakes, oceans, ponds, streams and other large bodies of water create mild, temperate climates by cooling surrounding air in the summer and retaining warm air during the winter. In general, larger bodies of water produce the most dramatic effects on surrounding climate. Water takes longer to heat and cool than land surfaces; this delay causes water to retain heat during the winter and remain at a lower temperature in the summer.
In addition to size, the number and type of water bodies in a given area affects climate. Other factors, such as wind currents and proximity to water, affect conditions as well. Latitude plays a smaller role in controlling climate as two places with the same latitude may differ in climates based on the presence or absence of water. Southern Ontario, for instance, receives more precipitation, but a smaller annual change in temperature due to the presence of the Great Lakes. The surrounding region experiences mild winters and summers. In contrast, other regions of Canada at the same latitude, such as the flat interior plains, experience more pronounced temperature changes during the winter and summer months. Despite having colder winters and hotter summers, however, this area receives less precipitation. Bodies of water also produce more storms, which take the form of snow storms during the winter and thunderstorms during the summer.