Oceanicity is a measure of the degree to which the climate of a region is influenced by a maritime airflow from the oceans. In contrast to continental climates, maritime climates experience generally cool summers and mild winters, with a much smaller annual temperature range. This is because water has a much higher heat capacity than soil and rock. Seawater takes a long time to warm up in summer, but once heated it retains its energy long after the surrounding land has cooled down, helping to moderate the climate. Maritime climates generally are fairly humid, accompanied by considerable amounts of precipitation, since the main moisture source is not very far away.
The British Isles experiences a typically maritime climate, with prevailing southwesterly winds from the Atlantic Ocean. The maritime air masses that influence this part of the world are particularly mild on account of the warming influence of the Gulf Stream. The annual average temperature range in the UK is only about 10C. Although the west coasts of Canada and Alaska experience maritime climates, the absence of an equally significant warm Pacific current in the mid latitudes means that these regions are generally colder in winter, with more precipitation falling as snow.