An oceanic climate, also known as a marine climate or maritime climate, is the temperate climate sub-type in Köppen classification represented as Cfb, typical of west coasts in higher middle latitudes of continents, generally featuring cool to warm summers and cool to mild winters (for their latitude), with a relatively narrow annual temperature range and few extremes of temperature. Oceanic climates can be found in both hemispheres generally between 40 and 60 degrees latitude, with subpolar versions extending to 70 degrees latitude in some coastal areas. Other varieties of climates usually classified together with these include subtropical highland climates, represented as Cwb or Cfb, and subpolar oceanic or cold subtropical highland climates, represented as Cfc or Cwc. Subtropical highland climates occur in some mountainous parts of the subtropics or tropics, some of which have monsoon influence, while their cold variants and subpolar oceanic climates occur near polar or Tundra climate regions.
Poleward of the latter is a subtype of it, the subpolar oceanic climate (Köppen Cfc), with long but relatively mild (for their latitude) winters, and cool and short summers with average temperatures of at least for one to three months. Examples in the Northern Hemisphere include parts of coastal Iceland, the coast of Norway north of Bodø, the Scottish Highlands, the mountains of Vancouver Island, and Haida Gwaii in Canada. In the Southern Hemisphere examples include extreme southern Chile and Argentina (such as Punta Arenas and Ushuaia), the Falkland Islands, the Tasmanian Central Highlands, and parts of New Zealand.
The North Atlantic Gulf Stream, a tropical oceanic current that passes north of the Caribbean and up the East Coast of the United States to North Carolina, then heads east-northeast to the Grand Banks of Newfoundland, is thought to greatly modify the climate of northwest Europe. As a result of the North Atlantic Current, west coast areas located in high latitudes like Ireland, the UK, and Norway have much milder winters (for their latitude) than would otherwise be the case. The lowland attributes of western Europe also help drive marine air masses into continental areas, enabling cities such as Dresden, Prague, and Vienna to have maritime climates in spite of being located well inland from the ocean.
Western Europe is almost exclusively oceanic between 45°N to 54.913°N; including most of France (away from the Mediterranean), nearly all of Belgium, the Netherlands, Austria, most of Luxembourg, most of Denmark, western Germany, northwestern Switzerland, south coast and western areas of Norway north to Skrova and extreme southern Sweden.
While most of Southern Europe is climatically Mediterranean, some parts of Southern Europe also have oceanic climates. However, these instances of the climate are highly variable, and often somewhat anomalous. The north coast of Spain, the western Azores off the coast of Portugal are too wet in summer to be Mediterranean, and too mild in summer to be humid subtropical, though they often have winter means above , unusual for European oceanic climates.
Another anomalous case can be found in northwestern Turkey, including northern Istanbul. These places are, in a strict air-mass sense, not oceanic: they are affected by southerlies directly from the Mediterranean, and polar intrusions from Siberia. Yet their position near the Black Sea makes them too wet in summer to be Mediterranean, too mild during winter to be humid continental, and not hot enough in summer to be humid subtropical; therefore Köppen classifies them as oceanic. Despite their anomalous position, however, their temperatures, around in winter and in summer, are not wholly atypical for European oceanic climates.
Some Eastern European regions such as the north of Croatia and Serbia and some parts of the Czech Republic, also have oceanic climates; these are generally near the boundary for being humid continental.
The line between oceanic and continental climates in Europe runs in a generally northwest to southeast direction. For example, western Germany is more impacted by milder Atlantic air masses than eastern Germany. Thus, winters across Europe become colder to the east, and (in some locations) summers become hotter. The line between oceanic Europe and Mediterranean Europe normally runs west to east and is related to changes in precipitation patterns and differences to seasonal temperatures; although intrusions of polar air, remnants of marine air-masses, and higher summer precipitation can create oceanic climates in Eastern Europe and transcontinental regions as far south as 40°N.
The oceanic climate is prevalent in the more southerly parts of Oceania. A mild maritime climate is in existence in New Zealand. In Australia, the climate is found in Tasmania, southern half of Victoria and southeastern New South Wales (southwards from Wollongong).
The hinterland of the northern coast of Turkey, features this climate. Additionally, parts of the northeastern coast of Honshu, such as Mutsu, Aomori in Japan, feature this climate, which is rare in Asia due to the lack of a west coast in the middle latitudes.
Western ease temperatures and moderates the winter, especially if warm Ocean current are present, and cause cloudy weather to predominate. Precipitation is constant, especially in colder months, when temperatures are warmer than elsewhere at comparable latitudes. This climate can occur farther inland if no mountain ranges are present or nearby. As this climate causes sufficient moisture year-round without permitting deep snow cover, vegetation typically prospers in this climate. Deciduous trees are predominant in this climate region. However, conifers such as spruce, pine, and Cedrus are also common in few areas, and fruits such as , , and can often be cultivated here.
In the hottest month, the average temperature is below , and at least four months feature average temperatures higher than . The average temperature of the coldest month must not be colder than , or the climate will be classified as continental. The average temperature variations in the year are between , with average annual temperatures between . Rain values can vary from , depending on whether mountains cause orographic precipitation. Frontal cyclones can be common in marine west coast regions, with some areas experiencing more than 150 rainy days annually, but strong storms are rare.
Cfb climates are predominant in most of Europe except the northeast, as global temperatures became warmer towards late 20th and early 21st century. They are the main climate type in New Zealand and the states of Tasmania, Victoria, and southeastern New South Wales (starting from the Illawarra region). In North America, they are found mainly in Vancouver Island and neighbouring parts of British Columbia, as well as many coastal areas of southeast Alaska. There are pockets of this iteration of Cfb climates in South American countries, mostly in regions of southern Chile and Argentina, parts of the provinces of Chubut Province, Santa Cruz, and southeast Buenos Aires province in Argentina. In Western Asia, the climate can be found on the Black Sea coast of northern Turkey and Georgia, often transitional to humid subtropical. While Cfb zones are rare in Africa, one dominates the coastline of the Eastern Cape in South Africa.
The climate subtype can also be found in Nantucket, Massachusetts (in the immediate west and northwest in transition for humid continental, the remainder of Cape Cod) and northeastern Georgia both in the eastern United States. It is also found in the highest portions of the Brazilian state of Bahia and Roraima (in transition or strongly influenced for Cwb), Brønnøy Municipality in Nordland at 65.28 °N (Norway north-central coast), the provinces of Sabah (northeastern Malaysia), and Balochistan, Pakistan. Although there are more or less rare places associated with relatively isolated mountainous regions (e.g., North Oceania islands and China).
Subtropical highland climates with uniform rainfall ( Cfb) usually have rainfall spread relatively evenly throughout the year, similar to other oceanic climates, but unlike these climates, they have a high diurnal temperature variation and low humidity, owing to their inland location and relatively high elevation. Subtropical highland climates with monsoon influence ( Cwb) have distinctive wet season and dry season.
In locations outside the tropics, other than the drying trend in the winter, subtropical highland climates tend to be essentially identical to an oceanic climate, with mild summers and noticeably cooler winters, plus, in some instances, some snowfall. In the tropics, a subtropical highland climate typically features mild weather year-round. Temperatures there remain relatively constant throughout the year and snowfall is seldom seen due to warmer winters than most oceanic climates.
Areas with this climate feature monthly averages below but above either or depending on isotherm used. At least one month's average temperature is below . Without their elevation, many of these regions would likely feature either humid subtropical or tropical climate climates.
This type of climate exists in parts of east, south and southeastern Africa, interior southern Africa and elevated portions of eastern Africa as far north as Ethiopia and of western Africa (west region of Cameroon) up to the southwestern Angola highlands also share this climate type. It also exists in the exposed areas of the High Atlas, some mountainous areas across southern Europe, mountainous sections of North America, including parts of the southern Appalachians and the Central America Volcanic Arc. In South America, it can be found mainly in temperate mountainous areas in the Tropical Andes, Venezuelan Coastal Range, the highest elevations of Serra do Mar in Southeastern Brazil, and tepuis of the Guiana Shield, The highest elevations of the Brazilian Highlands, and due to variations in rainfall and temperature patterns in some places of the Tropical Andes in Bolivia, Perú, Ecuador, Colombia and Venezuela. Most of Yunnan and mountainous areas across Southeast Asia, parts of the Himalayas, parts of Sri Lanka, and parts of the Hawaiian Islands of Maui and Hawaii. In the Caribbean, only the peaks in the highest mountain ranges have this climate (including the Blue Mountains in Jamaica and Cerro Maravilla in Puerto Rico), with only Hispaniola's Cordillera Central and Chaîne de la Selle having significant urban settlements under this climate zone, such as cities like Kenscoff in Haiti and Constanza in the Dominican Republic.
This variant of an oceanic climate is found in parts of coastal Iceland, the Faroe Islands, upland/mountainous parts of Scotland and Northern England, northwestern coastal areas of Norway (most of Lofoten, Vesterålen, warmest part of Tromsø reaching to 71°N on some islands), uplands/highlands in western Norway, the Aleutian Islands of Alaska and northern parts of the Alaskan Panhandle, the southwest of Argentina and Chile, and a few highland areas of Tasmania, and the Australian Alps and Southern Alps.
Small areas in Yunnan, Sichuan; parts of Bolivia and Peru; and parts of Mount Kilimanjaro in Tanzania have summers sufficiently short to be Cwc with fewer than four months over . This is the cold variant of the monsoon-influenced subtropical highland climate. El Alto, Bolivia is one of the few confirmed cities that features this variation of the subtropical highland climate.
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