Visitors to the Outer Hebrides Islands off the west coast of Scotland might be surprised to find palmetto trees, transplanted from warmer climes, surviving at 58 ° latitude. Across the Atlantic, along the coast of Labrador, icebergs drift southward to waters south of 50°. This environmental disparity illustrates that latitude and altitude are not the only determining factors of local climate. The ocean and its currents play an important role in the weather and climate of coastal and inland regions.

In 1770 Benjamin Franklin drew a map illustrating the course of the Gulf Stream, the dominant surface current of the Atlantic Ocean. This strong flow moves north along the east coast of North America from the West Indies, past Newfoundland, where it melts icebergs delivered from Labrador, and crosses the Atlantic to Scotland and Scandinavia, where its warm waters allow palmettos to survive and...