The big facts page

180 climate zone facts, all checked

Every fact on this site in one place, each linked to the Met Office, NOAA or Encyclopaedia Britannica. Our build checks each one against the source text; see the sources page.

Climate and climate zones

1 Climate is the general weather of a place over a long period: rainfall, temperature, snow and the rest. Met Office: What is climate?
2 A region’s climate is usually worked out over 30 years of weather. Met Office: What is climate?
3 The big difference between weather and climate is time: weather is hours or days, climate is years or decades. Met Office: What is climate?
4 The Met Office’s way of putting it: climate decides which clothes are in your wardrobe; weather decides what you wear today. Met Office: What is climate?
5 Most of the energy in Earth’s climate system comes, in the end, from the Sun. Met Office: What is climate?
6 The word climate comes from the ancient Greek klíma, “an inclination or slope”, as in the slope of the Sun’s rays, and also meant a latitude zone of Earth. Encyclopaedia Britannica: climate
7 Britannica says climate is not just the “average weather”: it includes the extremes, the variability and how often things happen. Encyclopaedia Britannica: climate
8 NOAA also measures climate over 30-year intervals. NOAA JetStream: Climate zones
9 Climate zones are areas with distinct climates. They can follow weather patterns, latitude, or communities of plants and animals. Met Office: Climate zones
10 There are many climate classification systems, each drawing its zones from different climate factors. Met Office: Climate zones
11 Climate zones help farmers and gardeners work out which plants will grow best where they live. Met Office: Climate zones
12 Zones also help scientists understand where plants and animals can live, including species that may be under threat from a shifting climate. Met Office: Climate zones
13 Roughly, the zones run by latitude: tropical near the equator, dry just north and south of the tropics, temperate beyond, and polar only in the Arctic and Antarctic. Met Office: Climate zones
14 The western and eastern sides of a continent can have very different climates, because of the direction of the prevailing winds. Met Office: Climate zones
15 As the climate warms, the map of climate zones will change too. Met Office: Climate zones
16 On the Met Office’s world map, tropical climates sit in central Africa, central America and parts of Asia. Met Office: Climate zones
17 Dry climates cover northern and southern Africa, most of Australia, parts of Asia and the western tips of the Americas. Met Office: Climate zones
18 Continental climates are mostly in the interiors of Canada and Russia, with some in the northern USA. Met Office: Climate zones
19 Polar climates reach the far north of Canada and Russia, Greenland, and the Arctic and Antarctic. Met Office: Climate zones
20 A microclimate is a small area with a different climate from its surroundings, caused by things like lakes, hills or buildings. Met Office: Climate zones
21 A microclimate can be as small as a few square metres, such as a shady corner of a garden. Met Office: Climate zones
22 Cities make their own microclimates: buildings and hard surfaces soak up heat by day, creating an urban heat island. Met Office: Climate zones
23 For the precise, up-to-date map of the zones and how they will change, the Met Office points to a 2018 paper by Beck and colleagues. Met Office: Climate zones

The Köppen system

24 The climatologist Wladimir Köppen first developed his climate classification in 1884, and scientists all over the world still use versions of it. Met Office: Climate zones
25 The Köppen system is one of the most widely used ways of sorting climates into zones. Met Office: Climate zones
26 Köppen sorts climates into five main groups: tropical (A), dry (B), temperate (C), continental (D) and polar (E). Met Office: Climate zones
27 Each group is then split up, first by when the rain falls in the year and then by temperature. Met Office: Climate zones
28 Köppen published his first full scheme in 1900 and a revised version in 1918, and kept revising it until he died in 1940. Encyclopaedia Britannica: Köppen climate classification
29 Wladimir Köppen lived from 1846 to 1940. NOAA calls him a German climatologist and amateur botanist. NOAA JetStream: Climate zones
30 Köppen worked with Rudolf Geiger, which is why it is often called the Köppen-Geiger system. NOAA JetStream: Climate zones
31 Köppen wanted his climate boundaries to line up with the vegetation zones (biomes) that were being mapped for the first time in his lifetime. Encyclopaedia Britannica: Köppen climate classification
32 Group B is the odd one out: it is defined by dryness, while every other group is defined by temperature. Encyclopaedia Britannica: Köppen climate classification
33 Evaporation is hard to measure, so Köppen used temperature as a stand-in for it in his dryness formula. Encyclopaedia Britannica: Köppen climate classification
34 Dry climates are split into arid (BW) and semi-arid (BS), with h added for warm and k for cold. Encyclopaedia Britannica: Köppen climate classification
35 Tropical climates come in three kinds: Af (no dry season), Am (a short dry season) and Aw (a dry winter). Encyclopaedia Britannica: Köppen climate classification
36 Polar climates are split into tundra (ET) and snow and ice (EF). Encyclopaedia Britannica: Köppen climate classification
37 C and D climates get a second letter: f for no dry season, w for a dry winter, s for a dry summer. Encyclopaedia Britannica: Köppen climate classification
38 A third letter, a, b, c or d, describes how warm the summer is or how cold the winter is. The d only turns up in D climates. Encyclopaedia Britannica: Köppen climate classification
39 Köppen didn’t include mountains as their own group, but a highland group, H, is sometimes added for land above 1,500 metres. Encyclopaedia Britannica: Köppen climate classification
40 Much of the UK is Cfb: temperate (C), with no dry season (f) and a warm summer (b). Met Office: Climate zones
41 Critics point out that droughts and cold snaps can matter to plants as much as the averages Köppen used. Encyclopaedia Britannica: Köppen climate classification
42 Other critics say sunshine and wind matter to plants too, and Köppen’s scheme leaves them out. Encyclopaedia Britannica: Köppen climate classification
43 Even so, Britannica calls Köppen’s system the most popular climate classification in use today. Encyclopaedia Britannica: Köppen climate classification
44 Britannica’s table of the rules is adapted from Critchfield’s General Climatology (1983) and a 2007 world map by Peel, Finlayson and McMahon. Encyclopaedia Britannica: Köppen climate classification
45 In the rules, the “summer half” of the year means April to September in the northern hemisphere and October to March in the southern. Encyclopaedia Britannica: Köppen climate classification
46 Any climate that passes the dryness test is a B, whatever else it is like. Encyclopaedia Britannica: Köppen climate classification
47 In 2007 the scientists Peel, Finlayson and McMahon published an “Updated World Map of the Köppen-Geiger Climate Classification”. Encyclopaedia Britannica: Köppen climate classification
48 The highland zone in Britannica’s rule table comes from G.T. Trewartha’s book An Introduction to Climate (4th edition, 1968). Encyclopaedia Britannica: Köppen climate classification

The Köppen rules

49 Rule for A: the coolest month averages 18 °C or more. Encyclopaedia Britannica: Köppen climate classification
50 Af: the driest month still gets at least 60 mm of rain. Encyclopaedia Britannica: Köppen climate classification
51 Am: the driest month gets under 60 mm, but at least 100 minus the yearly rainfall divided by 25. Encyclopaedia Britannica: Köppen climate classification
52 Rule for B (rain mostly in summer): yearly rainfall in mm is less than 20 times the yearly mean temperature plus 280. Mostly in winter: less than 20 times the temperature. Spread out: 20 times the temperature plus 140. Encyclopaedia Britannica: Köppen climate classification
53 BW (desert): rainfall is under half the dryness limit. BS (steppe): between half and the full limit. Encyclopaedia Britannica: Köppen climate classification
54 In dry climates, h means a yearly mean of 18 °C or more, and k means under 18 °C. Encyclopaedia Britannica: Köppen climate classification
55 Rule for C: warmest month 10 °C or more, coldest month below 18 °C but above −3 °C. Encyclopaedia Britannica: Köppen climate classification
56 Rule for D: warmest month 10 °C or more, coldest month −3 °C or lower. Encyclopaedia Britannica: Köppen climate classification
57 Third letters: a, warmest month 22 °C or above; b, at least four months of 10 °C or more but warmest under 22 °C; c, one to three months of 10 °C or more. Encyclopaedia Britannica: Köppen climate classification
58 d: the coldest month is below −38 °C. Encyclopaedia Britannica: Köppen climate classification
59 Rule for E: the warmest month is below 10 °C. ET: warmest month above 0 °C. EF: warmest month 0 °C or below. Encyclopaedia Britannica: Köppen climate classification
60 s (dry summer): the driest summer month gets under 30 mm and less than a third of the wettest winter month. Encyclopaedia Britannica: Köppen climate classification
61 w (dry winter): the driest winter month gets less than a tenth of the wettest summer month. Encyclopaedia Britannica: Köppen climate classification
62 The Met Office describes temperate climates with a 0 °C line instead: coldest month between 0 °C and 18 °C, at least one month above 10 °C. Met Office: Climate zones
63 NOAA describes D climates with the −3 °C line: warmest month above 10 °C, coldest month below −3 °C (27 °F). NOAA JetStream: Climate zones

Why zones differ: sunlight and moving air

64 Global circulation is the large-scale movement of air that carries heat and moisture around the planet. Met Office: Global circulation patterns
65 It is driven by uneven heating: the equator gets more direct sunlight than the poles. Met Office: Global circulation patterns
66 Each hemisphere has three big circulation cells: the Hadley, Ferrel and Polar cells. Met Office: Global circulation patterns
67 In the Hadley cell, trade winds blow towards the equator, the warm air rises into towering rain clouds, then sinks over the subtropics, making high pressure over deserts like the Sahara. Met Office: Global circulation patterns
68 The Hadley cell reaches from the equator to about 30–40° latitude. Met Office: Global circulation patterns
69 The Ferrel cell, between about 30–40° and 60–70°, works like a gear between the other two. Met Office: Global circulation patterns
70 The Polar cell is the smallest and weakest. Air sinks at the poles and flows away from them at the surface. Met Office: Global circulation patterns
71 Earth’s spin bends moving air to the right in the northern hemisphere and to the left in the southern: the Coriolis effect. Met Office: Global circulation patterns
72 Together the three cells work like a global conveyor belt, shaping the winds and where deserts and rainforests are found. Met Office: Global circulation patterns
73 The Hadley cell is named after George Hadley, an English physicist who proposed a single circulation for each hemisphere in 1735. NOAA JetStream: Global atmospheric circulations
74 The Ferrel cell was proposed by William Ferrel in 1856, the first to explain the westerly winds between 35° and 60°. NOAA JetStream: Global atmospheric circulations
75 High-pressure bands sit at about 30° north and south and at each pole; low-pressure bands at the equator and at 50–60°. NOAA JetStream: Global atmospheric circulations
76 Look at a globe and you’ll see lots of deserts along 30° north and south, including the American Southwest, northern Africa and Australia. NOAA JetStream: Global atmospheric circulations
77 The band between 50° and 60°, including the British Isles, tends to be wetter, especially on the west coasts of continents. NOAA JetStream: Global atmospheric circulations
78 Without Earth’s tilt, spin and oceans, the circulation would be one simple loop from equator to pole in each hemisphere. NOAA JetStream: Global atmospheric circulations

Oceans and continents

79 The UK is at the same latitude as most of Canada but has a much milder climate, thanks to the Gulf Stream and the North Atlantic. Met Office: Climate zones
80 The Gulf Stream is a warm, fast Atlantic current that starts at the tip of Florida and carries tropical warmth towards Europe. Met Office blog: What is the Gulf Stream and how does it affect UK weather?
81 It is part of a bigger ocean conveyor belt, the Atlantic Meridional Overturning Circulation (AMOC), driven by differences in water temperature and saltiness. Met Office blog: What is the Gulf Stream and how does it affect UK weather?
82 As the water cools and gets saltier on its way north, it becomes denser and sinks, then creeps back towards the equator several kilometres down. Met Office blog: What is the Gulf Stream and how does it affect UK weather?
83 Without the Gulf Stream, the UK’s climate would be much colder. Met Office blog: What is the Gulf Stream and how does it affect UK weather?
84 Cities in Canada at the same latitude as London often have much harsher winters. Met Office blog: What is the Gulf Stream and how does it affect UK weather?
85 Continental climates are like temperate ones but with bigger extremes, because they sit far inland, away from the calming effect of the sea. Met Office: Climate zones
86 On marine west coasts the yearly temperature range is only about 10–15 °C, roughly half that of the continental interior at the same latitude. Encyclopaedia Britannica: marine west coast climate

Tropical climates (A)

87 Tropical rainforest climates are found in South America, Africa and South-east Asia, either side of the equator. Met Office: Climate zones
88 In a tropical rainforest climate, average temperatures are usually around 20–30 °C, with little change through the year. Met Office: Climate zones
89 Every month gets over 60 mm of rain, which feeds thick rainforest and some of the richest wildlife on land. Met Office: Climate zones
90 Tropical (A) climates form a nearly unbroken belt around Earth, mostly within 15° of the equator. Encyclopaedia Britannica: Köppen climate classification
91 In the tropics the difference between day and night is usually bigger than the difference between the warmest and coolest months. Encyclopaedia Britannica: Köppen climate classification
92 There, winter and summer mean little; wet and dry seasons set the rhythm of the year instead. Encyclopaedia Britannica: Köppen climate classification
93 Tropical monsoon climates have a season of heavy rain, linked to a seasonal change in wind direction. Met Office: Climate zones
94 Am climates are found mainly in southern and south-eastern Asia. Encyclopaedia Britannica: tropical monsoon and trade-wind littoral climate
95 In a monsoon climate the hottest weather usually comes at the end of the short dry season. Encyclopaedia Britannica: tropical monsoon and trade-wind littoral climate
96 The Asian monsoon brings summer rain as warm, moist sea air moves inland towards low pressure north of the Himalayas. Encyclopaedia Britannica: tropical monsoon and trade-wind littoral climate
97 In the Americas and Africa, Am climates are of the trade-wind kind: moist trade winds rise up mountains along narrow coastal strips. Encyclopaedia Britannica: tropical monsoon and trade-wind littoral climate
98 Tropical savanna climates have a more marked dry season than monsoon areas, and grassland rather than rainforest. Met Office: Climate zones
99 In a tropical wet-dry (Aw) climate, the dry season gets longer the further you go from the equator. Encyclopaedia Britannica: tropical wet-dry climate
100 Aw climates get about 50–175 cm of rain a year, mostly in heavy showers as warm air rises. Encyclopaedia Britannica: tropical wet-dry climate
101 The wet season comes when the rain belt near the equator, the intertropical convergence zone, moves overhead. Encyclopaedia Britannica: tropical wet-dry climate
102 A savanna is open country with scattered trees over a continuous layer of grass, growing where it is hot and seasonally dry. Encyclopaedia Britannica: savanna
103 The biggest savannas are in Africa, South America, Australia, India, the Myanmar–Thailand region and Madagascar. Encyclopaedia Britannica: savanna
104 Grasses, the main plants of savannas, appeared only about 50 million years ago. Encyclopaedia Britannica: savanna

Dry climates (B)

105 Dry and semi-dry climates cover about a quarter of Earth’s land, mostly in the belt between 15° and 30° latitude. Encyclopaedia Britannica: Köppen climate classification
106 Sinking air on either side of the tropics makes near-permanent high pressure over the subtropics. Skies stay almost cloud-free all year, and deserts form. Met Office: Climate zones
107 With no clouds to hold the heat in, deserts swing hugely between day and night: some of the hottest places on Earth drop below freezing at night. Met Office: Climate zones
108 Not all deserts are hot. In the Gobi Desert of east Asia, the yearly average temperature can be below 0 °C. Met Office: Climate zones
109 Most of Earth’s true tropical deserts lie between 15° and 30° latitude, where the Hadley cell’s air comes down. Encyclopaedia Britannica: tropical and subtropical desert climate
110 The driest deserts are best developed on the western sides of continents. Encyclopaedia Britannica: tropical and subtropical desert climate
111 Low-latitude deserts mostly get 0–25 cm of rain a year, but how unreliable it is matters more than the small totals. Encyclopaedia Britannica: tropical and subtropical desert climate
112 A desert averaging 5 cm of rain over ten years might have had 50 cm in one wet year and almost none in the other nine. Encyclopaedia Britannica: tropical and subtropical desert climate
113 Desert days and nights can differ by 35 °C when daytime highs over 40 °C are followed by a fast night-time drop. Encyclopaedia Britannica: tropical and subtropical desert climate
114 In some low-latitude deserts, fewer than 30 days a year have clouds. Encyclopaedia Britannica: tropical and subtropical desert climate
115 A steppe is a vast, treeless grassland that gets roughly 25–30 cm of rain a year. Encyclopaedia Britannica: steppe
116 The word steppe comes from the Russian for “flat grassy plain”. Encyclopaedia Britannica: steppe
117 The great Eurasian Steppe stretches some 8,000 km, from Hungary through Ukraine and Central Asia to Manchuria. Encyclopaedia Britannica: steppe
118 Rain decides it: a bit less and a steppe turns to desert, a bit more and it becomes savanna or forest. Encyclopaedia Britannica: steppe

Temperate climates (C)

119 Temperate climates cover most of western Europe, western and eastern parts of the USA, and eastern China. Met Office: Climate zones
120 C and D climates fill much of the middle and high latitudes, mostly from 25° to 70° north and south. Encyclopaedia Britannica: Köppen climate classification
121 Köppen’s scheme has six C climates and eight D climates. Encyclopaedia Britannica: Köppen climate classification
122 A Mediterranean climate is a temperate climate with dry summers and mild, wet winters. Met Office: Climate zones
123 Mediterranean climates are usually on the western coasts of continents, between about 30° and 45° latitude. Encyclopaedia Britannica: Mediterranean climate
124 Besides the Mediterranean itself, much of California has this climate, as do parts of Western Australia, Chile and South Africa. Met Office: Climate zones
125 Mediterranean climates have their own kinds of scrubland: maquis around the Mediterranean, chaparral in California and fynbos in South Africa. Met Office: Climate zones
126 In the Köppen-Geiger-Pohl system, Mediterranean climates are Csa and Csb. Encyclopaedia Britannica: Mediterranean climate
127 Mediterranean climates get about 35–90 cm of rain a year. Encyclopaedia Britannica: Mediterranean climate
128 Only in Europe, where the Mediterranean Sea fills that latitude, does this climate reach far inland from the coast. Encyclopaedia Britannica: Mediterranean climate
129 Humid subtropical climates sit on the eastern sides of continents, between 20° and 35° latitude. Encyclopaedia Britannica: humid subtropical climate
130 In humid subtropical climates the warmest months average about 27 °C, with warm, sticky nights. Encyclopaedia Britannica: humid subtropical climate
131 In eastern and southern Asia the monsoon gives a version with a clearly dry winter, labelled Cwa. Encyclopaedia Britannica: humid subtropical climate
132 Marine west coast climates are mild, with few extremes and plenty of rain or drizzle in every month. Encyclopaedia Britannica: marine west coast climate
133 They sit on the western sides of continents, between 35° and 60° latitude, beyond the Mediterranean zone. Encyclopaedia Britannica: marine west coast climate
134 Marine west coast climates are labelled Cfb and Cfc. Encyclopaedia Britannica: marine west coast climate
135 Many places with this climate get rain on more than 150 days a year, though it is often light. Encyclopaedia Britannica: marine west coast climate
136 Lowland yearly averages are usually 7–13 °C, and summer months rarely average above 20 °C. Encyclopaedia Britannica: marine west coast climate
137 In Europe the Alps and Pyrenees run east–west, so this climate reaches some 2,000 km inland, into eastern Germany and Poland. Encyclopaedia Britannica: marine west coast climate
138 Where wet sea winds hit mountains, totals can go above 500 cm a year. Encyclopaedia Britannica: marine west coast climate

Continental climates (D)

139 Humid continental climates have big swings between hot summers and cold winters. Encyclopaedia Britannica: humid continental climate
140 They are found between 30° and 60° north in central and eastern North America and Asia. Encyclopaedia Britannica: humid continental climate
141 D climates are almost all in the northern hemisphere, because the southern hemisphere has hardly any land at those latitudes. Encyclopaedia Britannica: humid continental climate
142 Snow often lies continuously for one to four months in many parts. Encyclopaedia Britannica: humid continental climate
143 The frost-free season lasts from under 150 to about 200 days a year. Encyclopaedia Britannica: humid continental climate
144 Humid continental climates are Dfa, Dfb, Dwa and Dwb. Encyclopaedia Britannica: humid continental climate
145 The taiga, or boreal forest, is the great northern forest of cone-bearing evergreen trees, with long winters. Encyclopaedia Britannica: taiga
146 The taiga covers about 17 per cent of Earth’s land, in a belt around the far north. Encyclopaedia Britannica: taiga
147 Its trees are mostly pine, spruce, larch and fir, and they reach further north than any other trees on Earth. Encyclopaedia Britannica: taiga
148 Taiga is Russian for “land of the little sticks”. Encyclopaedia Britannica: taiga
149 The continental subarctic climate is Dfc, Dfd, Dwc and Dwd. Encyclopaedia Britannica: Köppen climate classification

Polar climates (E)

150 A polar climate has no month averaging above 10 °C. Met Office: Climate zones
151 In an ice cap climate no month averages above 0 °C. Plants can’t grow, and snow and ice pile up until they flow away as glaciers. Met Office: Climate zones
152 Ice cap climates also turn up very high up, such as on the highest Himalayan peaks. Met Office: Climate zones
153 If the warmest month averages between 0 °C and 10 °C, it is tundra: too short a growing season for trees, so dwarf shrubs, grasses and small plants instead. Met Office: Climate zones
154 Tundra animals include reindeer, musk ox and Arctic hare. Met Office: Climate zones
155 The summits of Ben Nevis and Cairn Gorm in Scotland are in the tundra climate zone. Met Office: Climate zones
156 When tundra climate happens high on mountains, it is usually called an Alpine climate. Met Office: Climate zones
157 The tundra climate lies between 60° and 75° latitude, mostly along the Arctic coasts of North America and Eurasia and the edges of Greenland. Encyclopaedia Britannica: tundra climate
158 Tundra winters are long: temperatures can stay below 0 °C for 6 to 10 months. Encyclopaedia Britannica: tundra climate
159 Tundra summer days can reach 15–18 °C, but the warmest month still averages under 10 °C. Encyclopaedia Britannica: tundra climate
160 Where the yearly mean is −9 °C or colder, the ground deep down stays frozen all year: permafrost. Encyclopaedia Britannica: tundra climate
161 Tundra usually gets less than 35 cm of rain and snow a year. Encyclopaedia Britannica: tundra climate
162 E climates are ruled by polar and Arctic air, at 60° and beyond. Encyclopaedia Britannica: Köppen climate classification
163 Northern Canada and Eurasia have some of the largest areas of tundra, and it also turns up on sub-Antarctic islands. Met Office: Climate zones

Mountain climates (H)

164 Highland climates were not part of Köppen’s own systems; the H group was added later for mountain areas. Encyclopaedia Britannica: highland climate
165 As a rough guide, mountains are like cooler, wetter versions of the lowland climates near them. Encyclopaedia Britannica: highland climate
166 Going up, temperature, air pressure, humidity and dust all fall. Encyclopaedia Britannica: highland climate
167 Mountains block moving air. The drier side downwind is called a rain shadow. Encyclopaedia Britannica: highland climate
168 Cold air can slide down from the heights and collect in low valleys as “frost pockets”. Encyclopaedia Britannica: highland climate
169 The snow line ranges from sea level in the subarctic to about 5,500 metres. Encyclopaedia Britannica: highland climate
170 NOAA describes highland climates as changing quickly over short distances as the ground rises. NOAA JetStream: Climate zones

The UK and the Isle of Man

171 The UK sits in a belt of mostly westerly winds, where low-pressure systems and fronts sweep in from the Atlantic. Met Office factsheet 4: Climate of the British Isles
172 By the time air reaches the UK, the sea has toned down its extremes, so summers are usually cooler than on the continent and winters milder. Met Office factsheet 4: Climate of the British Isles
173 Overall the south of the UK is usually warmer than the north, and the west wetter than the east. Met Office factsheet 4: Climate of the British Isles
174 The sea’s warming and cooling effect is mostly felt within 15 to 20 miles of the coast. Met Office factsheet 4: Climate of the British Isles
175 In the UK, January is usually the coldest month and July the warmest. Met Office factsheet 4: Climate of the British Isles
176 Sheltered low spots that get more, and harder, frosts are called frost hollows. Met Office factsheet 4: Climate of the British Isles
177 In summer the jet stream usually sits north of the UK, bringing more settled weather; in winter it shifts south. Met Office: Global circulation patterns
178 Britannica describes the Isle of Man’s climate as maritime temperate, with cool summers and mild winters. Encyclopaedia Britannica: Isle of Man
179 The Isle of Man’s average mean temperature is 4.9 °C in February and 14.3 °C in August. Encyclopaedia Britannica: Isle of Man
180 Its average yearly rainfall is about 1,140 mm. Encyclopaedia Britannica: Isle of Man