Why some places are steamy all year and others stay frozen, and how climate decides what can live there.
Hilo, on the island of Hawaii, gets about 120 inches of rain in an average year. Phoenix, Arizona, gets about 7. Both are warm places in the United States, so why the huge difference? The answer is climate, and climate depends on where a place sits on the planet: how far it is from the Equator, how high it is, how close it is to the ocean, and which way the wind blows. Climate helps decide which plants can grow there, and the plants help decide which animals can live there. On this page you'll learn how geographers sort the world into climate zones and biomes, and how to read the graph they use to compare places.
Weather or Climate?
People mix these two words up all the time, but geographers keep them apart.
Weather
What the air is doing in one place over a short time: today's temperature, rain, wind and clouds. A forecast of thunderstorms this afternoon is about weather. Weather can change from hour to hour.
Climate
The average of a place's weather over a long time, usually 30 years or more. "July in Washington, D.C., averages 81°F" is a fact about climate. Climate changes too, but slowly, over many years.
One way to remember it: weather is what you get on a given day, and climate is what you can expect. The National Oceanic and Atmospheric Administration (NOAA) publishes official 30-year averages called climate normals for thousands of U.S. weather stations. The current set covers 1991 to 2020, and a new set comes out every 10 years. Every climate graph on this page uses those normals.
Six Things That Shape Climate
Why is one place hot and another cold, one wet and another dry? Geographers point to a short list of causes. Most places are shaped by several of them at once.
1 Latitude
Near the Equator, the sun is high overhead and its rays hit the ground almost straight on, so the tropics are warm all year. Toward the poles, the sun sits lower in the sky. The same sunlight spreads out over a larger area, so it heats each spot less, and the poles are cold.
2 Elevation
Air gets colder as you go higher. In the standard atmosphere that pilots use, the temperature drops about 2°C (3.5°F) for every 1,000 feet you climb. Climbing a tall mountain can be like traveling toward a pole. Mount Kilimanjaro in Tanzania sits near the Equator, yet its climate is tropical at the bottom and polar at the top.
3 Distance from water
Land heats up and cools down faster than the ocean does. So the ocean keeps nearby coasts from getting very hot or very cold. Places deep inside a continent, far from the sea, have much bigger swings between summer and winter.
4 Ocean currents
Currents carry warm or cold water thousands of miles. The Gulf Stream carries warm water from the tropical Atlantic north and then across toward Europe, so western Europe is surprisingly mild for how far north it is. Cold water works the other way: San Francisco, cooled by cold water rising along its coast, is hardly warmer than Dublin, Ireland, even though it's more than 1,600 kilometers (1,000 miles) farther south.
5 Prevailing winds
Winds that blow mostly from one direction are called prevailing winds. Near the Equator, the trade winds blow from east to west. Between about 35° and 60° north and south, the westerlies blow from west to east. Wind coming off the ocean brings moist air. Belts of high air pressure near 30° north and south bring mostly dry, clear weather, which is one reason so many deserts lie near those latitudes, from the American Southwest and northern Africa to Australia.
6 Mountains and rain shadows
When wind pushes moist air up the side of a mountain range, the air cools and drops its water as rain and snow. By the time the air crosses the top and sinks down the other side, it's dry, and it warms as it sinks. The dry land on that side is called a rain shadow. The diagram below shows how it works.
How a rain shadow forms. The prevailing wind carries moist air from the ocean up the windward side of the mountains. The air rises, cools and forms clouds, so rain and snow fall on that side, and forests grow there. The air that crosses the peaks has lost most of its water. It sinks down the leeward side and warms, so the land there gets little rain. On a phone the drawing comes in two halves: the windward side, then the leeward side.
Real rain shadows: Death Valley, in California and Nevada, lies in the rain shadow of the Sierra Nevada mountains and is the lowest and driest place in North America. The Tibetan Plateau lies in the rain shadow of the Himalaya. On the coast of Peru, the Andes block moist air carried by the trade winds, and a cold ocean current, the Humboldt Current, cools the air near the shore. Together they make the capital city, Lima, a desert.
Climate Zones: The Köppen System
To compare climates around the world, many geographers use a system created by Wladimir Köppen, a German scientist who studied both plants and climate. Köppen noticed that the kinds of plants growing in a place depend mostly on its climate, so he drew his climate boundaries to match the edges of vegetation zones. He kept improving the system until his death in 1940. It sorts climates into five main groups, each named with a capital letter and defined by average monthly temperature and precipitation.
The five main Köppen climate groups, in kid-friendly terms
Group
The rule, simply put
Biomes you often find there
A: Tropical
Every month averages at least 18°C (64°F). There is no real winter.
Tropical rainforest, where it rains a lot every month; savanna, where there is a long dry season
B: Dry
More water could evaporate than falls as rain and snow. Very dry places are called arid; somewhat dry places are semiarid.
Desert; dry grasslands
C: Temperate
Mild winters: the coldest month is between −3°C (27°F) and 18°C (64°F). The warmest month is at least 10°C (50°F).
Temperate forest; some grasslands
D: Continental
Cold winters: the coldest month is −3°C (27°F) or colder. The warmest month is still at least 10°C (50°F).
Boreal forest; temperate forest and grassland
E: Polar
Even the warmest month averages below 10°C (50°F). If the warmest month is above freezing, it's a tundra climate. If every month is below freezing, it's an ice cap climate.
Tundra; polar ice
Dry (B) climates cover about a quarter of Earth's land, more than any other group. Some geographers add a sixth group, H, for highland climates, usually above about 1,500 meters (4,900 feet), where the climate changes quickly as you climb. A place's full Köppen code adds smaller letters after the capital. For example, Af means tropical with no dry season, and ET means polar tundra.
A Map of the World's Biomes
A biome is a large region of Earth with a similar climate and similar kinds of plants and animals. A biome can stretch across several continents: there is desert in Africa, Asia, Australia and both Americas. Compare this map with the Köppen groups above and you'll see why Köppen tied climate to plants.
A simplified map of the world's main land biomes. The long dashed line is the Equator, and the two dotted lines are the Tropic of Cancer (north) and the Tropic of Capricorn (south). Real biomes blend into each other, and the map leaves out small ones. In India and Southeast Asia, much of the land shown as savanna is actually dry tropical forest, which also has a long dry season. On a phone the map comes in two halves: the Americas, then Europe, Africa, Asia and Australia.
Map key
Color
Biome
Where to look on the map
Tropical rainforest
Along the Equator: the Amazon Basin in South America, central Africa around the Congo River, and the islands of Southeast Asia
Savanna
North and south of the African rainforests, central South America, northern Australia, and parts of India and Southeast Asia
Desert
Near 30° north and south: the Sahara, Arabia, central Australia, the American Southwest and Mexico, and the west coast of South America; also cold deserts in central Asia
Temperate grassland
The middle of North America, Argentina and Uruguay, and a long belt across Ukraine, Russia, Kazakhstan and Mongolia
Temperate forest
The eastern United States, western and central Europe, eastern China and Japan, and southern Chile
Boreal forest (taiga)
A wide belt across Canada, Alaska, Scandinavia and Russia, south of the tundra
Tundra
The far north of Alaska, Canada and Russia, and the edges of Greenland
Polar ice
Antarctica and most of Greenland
Mountains
The highest ranges, such as the Rocky Mountains, the Andes, the Himalaya and the Tibetan Plateau
The Major Biomes
Here are the eight land biomes on the map, from the hot, wet tropics to the frozen poles. Each card tells you where to find the biome, what its climate is like, and a few of the plants and animals that live there.
Tropical rainforest
Where
Near the Equator. The largest rainforests surround the Amazon River in South America and the Congo River in Africa. Others grow on the tropical islands of Southeast Asia.
Climate
Warm all year, with average daily temperatures of about 20 to 25°C (68 to 77°F). Rain falls every month: about 2,000 to 10,000 mm (79 to 394 in) a year, the most of any biome.
Plants
Giant trees whose tops can reach 75 m (about 250 ft) or more, with vines climbing toward the light and ferns below
Animals
Jaguars, two-toed sloths, spider and howler monkeys, scarlet macaws and keel-billed toucans in the Amazon
Did you know? Rainforests cover only about 2 to 6 percent of Earth's surface, yet more than half of the world's plant and animal species live in them.
Sources: NASA Earth Observatory, Mission: Biomes; National Geographic Education
Savanna
Where
North and south of the rainforests of Africa, and also in South America, Asia and Australia
Climate
Warm to hot all year, with a rainy season and a long dry season. Most of the year's rain falls in just a few months.
Plants
Grasses with scattered trees. Fire, grazing animals and elephants, which crush trees and shrubs, help keep the land open.
Animals
African elephants, lions, giraffes, zebras and ostriches in Africa; kangaroos and emus in Australia
Did you know? Every year more than one million wildebeest travel in a circle across Africa's Serengeti Plains, following the seasonal rains.
Sources: National Geographic Education
Desert
Where
Many lie near 30° north and south of the Equator. The Sahara, which covers much of northern Africa, is the world's largest hot desert.
Climate
Less than about 25 cm (10 in) of precipitation a year. Days can average 38°C (about 100°F), but the dry air lets heat escape fast, so nights can drop to about −4°C (25°F).
Plants
Cacti, which store water in their stems and use it very slowly, and plants that sprout, bloom and make seeds within a few weeks after rain
Animals
Black-tailed jackrabbits, in North American deserts such as the Sonoran and the Mojave
Did you know? Cairo, the capital of Egypt, lies in the Sahara. It is the largest desert city in the world.
Sources: NASA Earth Observatory, Mission: Biomes; National Geographic Education
Temperate grassland
Where
Between forests and deserts in the middle latitudes: the prairies of North America, the pampas of South America, the veldt of South Africa and the steppe of Asia and Eastern Europe
Climate
Warm summers and cold winters. About 500 to 900 mm (20 to 35 in) of precipitation a year.
Plants
Grasses, from tallgrass up to 2 m (6 ft) high where it's wetter to shortgrass where it's drier, plus wildflowers such as coneflowers. Few trees.
Animals
Bison, prairie dogs, pronghorn and coyotes on the prairie; greater rheas on the pampas; saiga antelope on the steppe
Did you know? Prairie soil is so rich that almost none of North America's prairie is left untouched; most of it is now farms and ranches.
Sources: National Geographic Education; NASA Earth Observatory, Mission: Biomes
Temperate forest
Where
The middle latitudes, between the tropics and the polar regions: the eastern United States, Canada, Europe, China and Japan
Climate
Four clear seasons, with hot summers and cold winters. About 750 to 1,500 mm (30 to 59 in) of precipitation a year, spread fairly evenly.
Plants
Broadleaf trees such as oaks, maples, beeches and hickories, which drop their leaves in fall and grow new ones in spring
Animals
Deer, squirrels and bears
Did you know? Dropping their leaves helps these trees survive cold winters. They grow a new set each spring.
Sources: NASA Earth Observatory, Mission: Biomes; National Geographic Education
Boreal forest (taiga)
Where
The cold subarctic, just south of the Arctic Circle and mostly between 50° and 60° north: Alaska, Canada, Scandinavia and Siberia
Climate
Long, very cold winters and short summers. About 300 to 900 mm (12 to 35 in) of precipitation a year.
Plants
Evergreen conifers such as spruce, pine and fir, plus mosses, lichens and mushrooms on the forest floor. The larch is one of the only trees here that drops its needles.
Animals
Moose, bears, lynx, owls and eagles. Most birds fly south for the winter.
Did you know? The world's largest taiga stretches about 5,800 km (3,600 mi) across Russia, from the Pacific Ocean to the Ural Mountains.
Sources: National Geographic Education; NASA Earth Observatory, Mission: Biomes
Tundra
Where
North of the boreal forest in Alaska, Canada, Russia, Greenland, Iceland and Scandinavia, and on very high mountains
Climate
Average temperatures below freezing for 6 to 10 months a year. Only about 150 to 250 mm (6 to 10 in) of precipitation a year, about as little as a desert.
Plants
Small shrubs, grasses, mosses, sedges and lichens, but almost no trees. Plants have only about 6 to 10 weeks a year that are warm enough to grow.
Did you know? Under the tundra lies permafrost, ground that stays frozen all year. The word tundra comes from tunturia, a Finnish word for a treeless hill.
Sources: National Geographic Education; NASA Earth Observatory, Mission: Biomes
Polar ice
Where
Antarctica and Greenland, home to the only two ice sheets left on Earth
Climate
Every month averages below freezing, so the snow never melts away. Antarctica gets so little new snow that it counts as one of the largest, driest deserts on Earth.
Size
The Antarctic Ice Sheet covers about 14 million km² (5.4 million sq mi). The Greenland Ice Sheet covers about 1.7 million km² (656,000 sq mi).
Thickness
Antarctica's ice cap is about 1.6 km (1 mile) thick
Did you know? The Antarctic Ice Sheet covers about eight times as much area as the Greenland Ice Sheet, yet snow builds up on Greenland more than twice as fast each year.
Sources: National Geographic Education; Encyclopaedia Britannica
Mountains are different. On the map, the highest mountain areas get their own color, because their biome changes as you climb. A tall mountain can have forest near the bottom and tundra near the top. Tundra found high on mountains is called alpine tundra.
Water and Ice
Aquatic biomes
Biomes aren't only on land. Geographers split water biomes into two kinds. Freshwater biomes, such as ponds, lakes, rivers and streams, have less than 1 percent salt. Marine biomes are salty: the open ocean, coral reefs, and estuaries, where a river's fresh water mixes with salt water from the sea. The ocean covers more than 70 percent of Earth's surface and holds about 97 percent of Earth's water.
Polar ice
Only two ice sheets are left on Earth today. The Antarctic Ice Sheet covers about 14 million square kilometers (5.4 million square miles). The Greenland Ice Sheet covers about 1.7 million square kilometers (656,000 square miles) and is the second-largest body of ice in the world. Antarctica's ice cap is about 1.6 kilometers (1 mile) thick, and so little snow falls there that Antarctica counts as one of the largest, driest deserts on Earth.
How to Read a Climograph
A climograph, or climate graph, shows a place's average temperature and precipitation for each month of the year on one chart. Once you can read one, you can often name the biome without being told where the place is.
A climograph for Washington, D.C. (Ronald Reagan Washington National Airport), using NOAA's 1991–2020 climate normals. The red line shows the average temperature each month, read on the left scale in °F. The blue bars show the average precipitation each month, read on the right scale in inches.
Check the scales. This graph has two. The left scale goes with the line (temperature), and the right scale goes with the bars (precipitation). Not every climograph puts them on the same sides, so always check.
Read the line. Find the highest and lowest points. In Washington, July is the warmest month at 81.0°F, and January is the coldest at 37.5°F. A line that rises high in summer and dips low in winter means the place has four seasons.
Read the bars. Find the tallest and shortest bars. July is the wettest month at 4.33 inches, and February is the driest at 2.62 inches. All twelve bars are fairly close in height, so precipitation is spread through the year. Add them up and you get the yearly total: 41.82 inches.
Match it to a biome. Four seasons and about 30 to 60 inches of precipitation, spread through the year, point to temperate forest. That fits: oak, maple and hickory forests are common in the region.
Rules of thumb for matching a climograph
Every month at or above 64°F (18°C): tropical. Heavy rain every month means tropical rainforest. A long dry season, with most of the rain in a few months, means savanna.
Less than about 10 inches (25 cm) of precipitation a year: desert, if it's warm enough for the ground not to stay frozen.
About 20 to 35 inches a year, with warm summers and cold winters: often temperate grassland.
About 30 to 60 inches a year, spread through the year, with four seasons: often temperate forest.
Long, very cold winters but a short summer with at least one month above 50°F (10°C): boreal forest.
Even the warmest month below 50°F, but some months above 32°F (0°C): tundra. Every month below 32°F: polar ice.
These are rules of thumb, not exact boundaries. Biomes blend into each other, and soil, fire and grazing animals matter too. The numbers come from the NASA, National Geographic and Köppen sources listed at the bottom of the page.
Game: Which Biome Am I?
Each round shows either a mystery climograph or a written clue. Decide which biome it describes. A right answer on your first try is worth 2 points, and on your second try, 1. There are 10 rounds, so a perfect game is 20.
Pick a biome with the buttons below, or press the number keys 1 to 4. Use Tab to move between buttons and Enter to press one.
Get ready…
Round 1 of 10 · Score 0 · Best 0
Dashed line: 32°F (freezing). Dotted line: 50°F.
How scoring works
Each game mixes five climographs and five written clues. The climographs use real NOAA averages from six U.S. weather stations, all drawn on the same scales so you can compare them. You get four biomes to choose from. A right answer earns 2 points on the first try and 1 point on the second. After two wrong tries the answer is shown and the round is worth 0. Your best score is saved only in this browser, as soon as a game ends.
Quiz: Climate and Biomes
Ten questions. Choose one answer for each, then check your score. You can try as many times as you like.
Talk About It
Which biome do you live in? Which of the six climate factors do you think matters most where you live, and why?
Hilo and Phoenix are both warm, but one gets about 17 times as much rain as the other. Using the climate factors, what could explain a difference that big?
Köppen drew his climate lines to match where plants grow. Why might plants be a good way to measure climate? What could make them a poor way?
The weather today is not the same as the climate. Think of a day when the weather where you live was very different from what the climate would lead you to expect. What happened?
Sources
NOAA National Ocean Service, What is the difference between weather and climate? and NOAA National Centers for Environmental Information, U.S. Climate Normals (weather versus climate; the 1991–2020 normals used for every climograph: Hilo, Phoenix, Dodge City, Washington Reagan National, Fairbanks and Utqiaġvik).
NOAA Global Monitoring Laboratory, What Is Climate? (climate factors, sun angle and latitude, land heating faster than the ocean, the Gulf Stream and Western Europe, San Francisco and Dublin, parts of a climate graph).
NOAA National Weather Service JetStream, Global Atmospheric Circulations (trade winds, westerlies, high pressure and deserts near 30° north and south).
National Geographic Education, All About Climate and Rain Shadow (climate factors, Kilimanjaro, Lima and the Humboldt Current, Death Valley and the Tibetan Plateau).
National Geographic Education, Köppen Climate Classification System (Köppen's aims, the five zones, cold steppe BSk, the highland group) and Encyclopaedia Britannica (Britannica Kids, Scholars), Köppen climate classification (the A to E temperature limits, highland heights, the share of land with dry climates).
Written by Marco for Jugami's World Geography course. The biome map, the rain-shadow diagram and all the climographs are original SVG illustrations made for this page. The map is simplified and the rain-shadow drawing is not to scale. The climographs are drawn from NOAA's 1991–2020 U.S. Climate Normals.
