Chapter 4 of 8

All 8 chapters
  1. 1The air and its layers, readunderstood
  2. 2Weather and air pressure, readunderstood
  3. 3Winds, monsoons and storms, readunderstood
  4. 4Climate zones, readunderstood
  5. 5Air pollution, readunderstood
  6. 6The greenhouse effect, readunderstood
  7. 7Climate change, readunderstood
  8. 8Responding to climate change, readunderstood

S4.14.4 Chapter 4

Climate zones

Kofi lives on the equator, near the coast, where it is warm and wet all year. His cousin lives on the equator too, high in the mountains, and wears a jumper. Why are their climates so different?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

  • You picked A. Read on. At the end, the chapter comes back to your guess.

  • You picked B. Read on. At the end, the chapter comes back to your guess.

  • You picked C. Read on. At the end, the chapter comes back to your guess.

  • You picked D. Read on. At the end, the chapter comes back to your guess.

By the end you can

  • Explain why climate differs with latitude, height and distance from the sea
  • Read a climate graph of temperature and rainfall

Weather is what the air is doing today. Climate is the pattern of the weather in a place over many years. Scientists usually take the average of about 30 years. A cold day in a hot place does not change its climate.

A table with the columns Of, Weather and Climate. Row 1, time: today for weather, years for climate. Row 2, case: rain now for weather, wet land for climate.OfWeatherClimatetimetodayyearscaserain nowwet land
Weather is today. Climate is the long pattern.

Three things above all decide a place’s climate: its latitude, its height, and its distance from the sea. Latitude is how far a place is north or south of the equator, measured in degrees.

Start with latitude. Near the equator the Sun climbs high in the sky, and its light comes down steeply. Near the poles the Sun stays low, and its light comes in at a slant. The same beam of light is then spread over a longer patch of ground.

Two pictures of the same width of sunlight reaching flat ground. On the left the Sun is high, labelled Sun high, and the light lands on a short patch. On the right the Sun is low, labelled Sun low, and the same light lands on a longer patch of ground. Labels: Sun high, Sun low.Sun highSun low
The same beam of sunlight. A low Sun spreads it over a longer patch, so each part of the ground gets less heat.

When the Sun is 30° above the horizon, the patch is twice as long as the beam is wide. Each part of the ground gets half the heat. Low Sun light also has to pass through more air, which takes in and scatters some of it. That is why the poles are cold and the tropics are hot.

Air pressure adds to the pattern. Near the equator the warm ground heats the air, and it rises. That gives a belt of low pressure, cloud and heavy rain. The air spreads out high up, cools, and sinks again near 30° of latitude. Sinking air is dry, so there are high pressure belts there, and many of the world’s great deserts.

A side view of the air from the equator, at 0 degrees, to a pole, at 90 degrees, with latitude along the bottom at 0, 30, 60 and 90 degrees. The ground is a hatched strip. Air rises at 0 and 60 degrees, with arrows going up, labelled L for low pressure and wet. Air sinks at 30 and 90 degrees, with arrows going down, labelled H for high pressure and dry. Arrows along the ground and at height join the rising places to the sinking places, in three loops. Labels: L, H, L, H, wet, dry, wet, dry, 0°, 30°, 60°, 90°, latitude.Lwet0°Hdry30°Lwet60°Hdry90°latitude
The air in three loops, from the equator to a pole. Where it rises it is wet, near 0° and 60°. Where it sinks it is dry, near 30° and 90°.

This is a rough picture. Land, sea and mountains bend it. But it explains the broad pattern. Climate scientists sort the world into five main kinds. Their edges are not sharp.

A table with the columns Zone and Climate. Row 1: tropical, hot and wet. Row 2: dry, little rain. Row 3: temperate, mild, changing. Row 4: cold, cold winters. Row 5: polar, cold all year.ZoneClimatetropicalhot and wetdrylittle raintemperatemild, changingcoldcold winterspolarcold all year
The five main climate zones. Tropical is nearest the equator, and polar is nearest the poles.

Now height. The air at the ground is warmed by the ground. The higher you climb, the further you are from that warm ground. In the lowest layer of the atmosphere the air gets about 6.5 °C colder for each km of height. This is why there are snow caps on mountains near the equator.

A mountain with dashed levels beside it. At 0 km it is 30 °C, at 1 km 23.5 °C, at 3 km 10.5 °C and at 5 km −2.5 °C. Each 1 km up is 6.5 °C colder. Labels: 0 km: 30 °C, 1 km: 23.5 °C, 3 km: 10.5 °C, 5 km: −2.5 °C.0 km: 30 °C1 km: 23.5 °C3 km: 10.5 °C5 km: −2.5 °C
A mountain where the sea level is 30 °C. Each km up is 6.5 °C colder.

Worked example

A town by the sea has a mean temperature of 28 °C. Another town on the same latitude is 2 km above sea level. What is its mean temperature?

  1. The air gets about 6.5 °C colder for each km.
  2. Two km is 2 × 6.5 = 13 °C of cooling.
  3. So the town is at 28 − 13 = 15 °C.

Answer: 15 °C

Last, the distance from the sea. Water holds heat well. In summer the sea is cooler than the land, and in winter it is warmer. Places near the sea are warmed and cooled by sea air, so their temperatures stay in a small range. Places far from the sea have a large range. A climate with a small range is called maritime, and one with a large range continental.

To see these differences, scientists draw a climate graph. It shows one place through a year. Each bar is the rainfall of a month, in mm, read on the right hand scale. The line is the mean temperature of each month, in °C, read on the left hand scale. The letters along the bottom are the months, January to December.

Here is Town A. It is hot all year and has a wet season. Which months are warm or wet depends on where in the world a place lies.

A climate graph for Town A. The left scale is temperature in °C, from 0 to 40. The right scale is rainfall in mm, from 0 to 320. Along the bottom are the months, J to D. The line stays between 25 and 28 °C all year. The bars are tall at the start and end of the year, 200 mm or more, and short in the middle, about 30 mm. Labels: °C, mm, 0, 10, 20, 30, 40, 80, 160, 240, 320, J, F, M, A, M, J, J, A, S, O, N, D.010203040080160240320°CmmJFMAMJJASOND
Town A: hot all year, with a wet season and a dry season.

Worked example

Use the graph of Town A. What is the range of the monthly temperature, and what is the total rainfall in the year? The rainfall of the months in mm is 250, 230, 260, 170, 90, 40, 30, 30, 50, 120, 200 and 240.

  1. The range is the hottest month minus the coldest month. The line peaks at 28 °C and falls to 25 °C.
  2. So the range is 28 − 25 = 3 °C.
  3. Add the bars. 250 + 230 + 260 + 170 + 90 + 40 = 1 040, and 30 + 30 + 50 + 120 + 200 + 240 = 670.
  4. The total is 1 040 + 670 = 1 710 mm.

Answer: 3 °C and 1 710 mm

Now compare two places at about the same latitude. Town B is on a coast. Town C is far inland. Both are in the northern hemisphere. They use the same scales, so you can compare them fairly.

A climate graph for Town B, on the coast. The left scale is temperature in °C, from −20 to 20. The right scale is rainfall in mm, from 0 to 120. The line stays between 5 and 17 °C all year. Rain falls in every month. Labels: °C, mm, −20, −10, 0, 10, 20, 60, 120, J, F, M, A, M, J, J, A, S, O, N, D.−20−1001020060120°CmmJFMAMJJASOND
Town B, on the coast. The temperature stays in a small range, and there is rain in every month.
A climate graph for Town C, far inland. The left scale is temperature in °C, from −20 to 20. The right scale is rainfall in mm, from 0 to 120. The line swings widely, from -12 °C at the start and end of the year, up to 20 °C in the middle. The bars are taller in the middle of the year. Labels: °C, mm, −20, −10, 0, 10, 20, 60, 120, J, F, M, A, M, J, J, A, S, O, N, D.−20−1001020060120°CmmJFMAMJJASOND
Town C, far inland. The temperature swings widely, from well below 0 °C to about 20 °C.

Town B has a small range. Town C has a large one. The sea keeps Town B mild all year. The land of Town C heats up and cools down fast. Other things matter too. Ocean currents carry warm or cold water along coasts. Mountains force air up, so one side of a range is wet and the other dry. The prevailing winds decide which places get sea air.

See it three ways

As a picture

A table with the columns Look at and It tells you. Row 1: the line, the temperature of each month. Row 2: the bars, the rainfall of each month. Row 3: high − low, the highest minus the lowest point of the line, the range.Look atIt tellslinetemperaturebarsrainfallhigh − lowrange

In words

Read the line on the left scale, in °C. Read the bars on the right scale, in mm. The range is the highest month minus the lowest. The total rain is all the bars added up.

In symbols

range = highest − lowest. total rain = month 1 + month 2 + … + month 12.

Try it

Draw a climate graph for a place you know

You need: a table of the mean temperature and rainfall of each month for a place, squared paper, a ruler and a pencil, two colours of pencil, or one pencil and a different kind of line.

Be safe: Use a blunt pencil and keep scissors, if you cut paper, away from small children. Take care crossing roads if you collect figures from a weather station or an office.

  1. Get the figures from a weather office, a school, a radio programme or an atlas. Or keep your own record for a year with the gauge from the earlier chapter.
  2. Draw two scales on squared paper: temperature in °C on the left, and rainfall in mm on the right. Make them line up at the 0 line.
  3. Draw a bar for each month for the rain. Mark a dot for each month for the temperature, and join the dots with a line.
  4. Work out the range and the total rainfall. Then say whether the place is wet or dry, and hot, mild or cold.

What you will see: You have turned a table of 24 numbers into one picture. It shows the climate of a place at a glance.

If you cannot try it, this is what happens.
A table with the columns Month, Mean temperature and Rain. Row 1: January, 5 °C, 90 mm. Row 2: February, 5 °C, 70 mm. Row 3: March, 7 °C, 65 mm. The table goes on for twelve months.MonthMeanRainJanuary5 °C90 mmFebruary5 °C70 mmMarch7 °C65 mm

A wrong idea many people have

A cold day means that the climate of a place is cold.

Why it feels right: Weather and climate are both about how warm, wet or windy a place is. So the two words seem to mean the same thing.

The test that breaks it: Look at the climate graph of Town A. Its coolest month is 25 °C. A single cold spell of 15 °C in a month would not change the average of 30 years of readings.

What is true: Weather is today. Climate is the pattern over many years, usually an average of 30. One cold day, or one hot summer, does not change the climate.

A wrong idea many people have

Mountains and the poles are cold because they are nearer to, or further from, the Sun.

Why it feels right: We think of the Sun as a fire: the closer we are, the warmer we are.

The test that breaks it: The Sun is about 150 million km away. A mountain 5 km high changes that distance by a tiny share. So does the whole width of the Earth, about 12 700 km. The real causes are the slant of the light, and the height above the warm ground.

What is true: The poles are cold because low Sun light is spread over more ground. High places are cold because the air gets about 6.5 °C colder for each km.

A wrong idea many people have

A desert is always hot.

Why it feels right: The deserts people see in pictures are hot, with sand and Sun.

The test that breaks it: A desert is a place with very little rain. Some deserts are cold, such as high deserts and the ice of the polar regions, which get very little snow. Desert air is dry, so heat escapes fast at night, and many hot deserts are cold after dark.

What is true: A desert is a place that is dry. It can be hot or cold.

Key words

climate
the pattern of weather in a place over many years, often the average of 30 years.
latitude
how far a place is north or south of the equator, in degrees.
climate graph
a graph of one place through the year: bars for the rain, a line for the temperature.
range
the highest value minus the lowest. For temperature, the hottest month minus the coldest.

Back to your guess

The answer is C: The air gets colder as you go up, about 6.5 °C for every km, so the mountain town is cooler.

In the lowest layer of the atmosphere the air gets about 6.5 °C colder for each km you climb. A town 2 km up is about 13 °C cooler than a town by the sea at the same latitude. Height is one of three big things that shape a climate. The others are latitude and the distance from the sea.

Check yourself

Try each one before you look. A wrong answer tells you where to go next.

  1. Which of these is a statement about climate, not weather?

    Tap your answer.

    1. Yes, that is right. Climate is the long pattern of weather in a place, over many years. A single day or night is weather.

    2. Not this one. That is about one morning. It is weather. Try another.

    3. Not this one. That is about one night. It is weather. Try another.

    4. Not this one. That is about today. It is weather. Try another.

    See the answer

    This town is hot and wet for most of the year, year after year.

    Climate is the long pattern of weather in a place, over many years. A single day or night is weather.

    • If you chose B: That is about one morning. It is weather.
    • If you chose C: That is about one night. It is weather.
    • If you chose D: That is about today. It is weather.

  2. Why is it so much colder at the poles than at the equator?

    Tap your answer.

    1. Not this one. The distance to the Sun is almost the same. What differs is the slant of the light. Go to S3.12.4. Try another.

    2. Not this one. The poles have air. The air there is cold because it gets so little heat from the slanting light. Try another.

    3. Not this one. The Sun shines on each pole for months of the year. It is low in the sky, so its light is weak. Try another.

    4. Yes, that is right. Near the poles the Sun is low. The same beam of light spreads over a longer patch of ground, so each part gets less heat.

    See the answer

    Sunlight comes in at a slant, so it is spread over a larger area of ground.

    Near the poles the Sun is low. The same beam of light spreads over a longer patch of ground, so each part gets less heat.

    • If you chose A: The distance to the Sun is almost the same. What differs is the slant of the light. Go to S3.12.4.
    • If you chose B: The poles have air. The air there is cold because it gets so little heat from the slanting light.
    • If you chose C: The Sun shines on each pole for months of the year. It is low in the sky, so its light is weak.

  3. A town by the sea has a mean temperature of 24 °C. Another town on the same latitude is 3 km above sea level. What is its mean temperature?

    Tap your answer.

    1. Not this one. That is the amount the air cools over 3 km, not the temperature. Take it away from 24 °C. Try another.

    2. Yes, that is right. Three km gives a cooling of 3 × 6.5 = 19.5 °C. So the temperature is 24 − 19.5 = 4.5 °C.

    3. Not this one. You added the cooling to 24 °C. Height makes the air colder, so you take it away. Go to S3.8.5. Try another.

    4. Not this one. The temperature does change with height. It falls by about 6.5 °C for each km. Try another.

    See the answer

    4.5 °C

    Three km gives a cooling of 3 × 6.5 = 19.5 °C. So the temperature is 24 − 19.5 = 4.5 °C.

    • If you chose A: That is the amount the air cools over 3 km, not the temperature. Take it away from 24 °C.
    • If you chose C: You added the cooling to 24 °C. Height makes the air colder, so you take it away. Go to S3.8.5.
    • If you chose D: The temperature does change with height. It falls by about 6.5 °C for each km.

  4. Two towns are on the same latitude. One is on a coast, the other far inland. Which has the larger difference between its hottest and coldest months?

    Tap your answer.

    1. Not this one. The sea keeps a coastal town mild all year. Water holds heat well, so the range is small. Go to S4.9.6. Try another.

    2. Not this one. Latitude is not the only thing. The sea changes how much a place warms and cools. Try another.

    3. Yes, that is right. The sea heats up and cools down slowly, so it keeps a coast steady. Far inland the land has a large range between its hottest and coldest months.

    4. Not this one. Rainfall is separate from the temperature range. Distance from the sea decides the range. Try another.

    See the answer

    The inland town, because the land warms and cools fast

    The sea heats up and cools down slowly, so it keeps a coast steady. Far inland the land has a large range between its hottest and coldest months.

    • If you chose A: The sea keeps a coastal town mild all year. Water holds heat well, so the range is small. Go to S4.9.6.
    • If you chose B: Latitude is not the only thing. The sea changes how much a place warms and cools.
    • If you chose D: Rainfall is separate from the temperature range. Distance from the sea decides the range.

  5. This is the climate graph of Town D. Which description fits it best?

    A climate graph for Town D. The left scale is temperature in °C, from 0 to 40. The right scale is rainfall in mm, from 0 to 80. Along the bottom are the months, J to D. The line is between 14 °C and 36 °C, and is highest in the middle of the year. The bars are very short in every month, under 10 mm. Labels: °C, mm, 0, 10, 20, 30, 40, 20, 40, 60, 80, J, F, M, A, M, J, J, A, S, O, N, D.010203040020406080°CmmJFMAMJJASOND
    Tap your answer.

    1. Yes, that is right. The line is high, up to 36 °C, and the bars are tiny in every month. This is a dry climate, like a desert.

    2. Not this one. The line is above 14 °C in every month, so it is not cold. The bars are very short, so it is not wet. Try another.

    3. Not this one. There is no wet season here. The bars are short in every month. Try another.

    4. Not this one. The temperature swings widely, and there is little rain in any month. Try another.

    See the answer

    Hot, with very little rain all year

    The line is high, up to 36 °C, and the bars are tiny in every month. This is a dry climate, like a desert.

    • If you chose B: The line is above 14 °C in every month, so it is not cold. The bars are very short, so it is not wet.
    • If you chose C: There is no wet season here. The bars are short in every month.
    • If you chose D: The temperature swings widely, and there is little rain in any month.

  6. Which of these is true of every desert?

    Tap your answer.

    1. Not this one. Some deserts are cold, and the ice of the polar regions is a desert too. Hot deserts are also cold at night. Try another.

    2. Not this one. Many deserts are rock or gravel. Sand covers only a part of the deserts of the world. Try another.

    3. Not this one. Plants and animals live in deserts. They are adapted to the dry. Try another.

    4. Yes, that is right. A desert is a dry place. It can be hot or cold, sandy or rocky, and it holds life that is adapted to the dry.

    See the answer

    It gets very little rain.

    A desert is a dry place. It can be hot or cold, sandy or rocky, and it holds life that is adapted to the dry.

    • If you chose A: Some deserts are cold, and the ice of the polar regions is a desert too. Hot deserts are also cold at night.
    • If you chose B: Many deserts are rock or gravel. Sand covers only a part of the deserts of the world.
    • If you chose C: Plants and animals live in deserts. They are adapted to the dry.

  7. From an earlier chapter

    What is a monsoon?

    Tap your answer.

    1. Not this one. The word means season. The rain belongs to the wet part of the cycle, but the monsoon is the wind. Go to S4.14.3. Try another.

    2. Yes, that is right. A monsoon is a wind that turns round with the season, bringing a wet season and a dry season.

    3. Not this one. A tropical storm is a spinning storm. A monsoon is a seasonal change in wind. Go to S4.14.3. Try another.

    See the answer

    A wind that changes direction with the season

    A monsoon is a wind that turns round with the season, bringing a wet season and a dry season.

    • If you chose A: The word means season. The rain belongs to the wet part of the cycle, but the monsoon is the wind. Go to S4.14.3.
    • If you chose C: A tropical storm is a spinning storm. A monsoon is a seasonal change in wind. Go to S4.14.3.

  8. Look at the graph of Town D. Its coldest month is 14 °C and its hottest month is 36 °C. What is the range of its monthly temperature?

    See the answer

    22 °C

    The hottest month is 36 °C and the coldest is 14 °C. The range is 36 − 14 = 22 °C.

  9. Look at the graph of Town D. The bars show 5, 5, 8, 4, 2, 0, 1, 2, 1, 2, 4 and 6 mm. What is the total rain in the year?

    See the answer

    40 mm

    Add the bars: 5 + 5 + 8 + 4 + 2 + 0 + 1 + 2 + 1 + 2 + 4 + 6 = 40 mm. That is very little rain.

  10. A town by the sea has a mean temperature of 30 °C. Another town on the same latitude is 4 km above sea level. What is its mean temperature, in °C?

    See the answer

    4 °C

    Four km gives a cooling of 4 × 6.5 = 26 °C. So the temperature is 30 − 26 = 4 °C.

  11. Sunlight in a beam 5 cm wide hits flat ground when the Sun is 30° above the horizon. How long is the patch of light, in cm? The patch is the width of the beam divided by sin 30°, which is 0.5.

    See the answer

    10 cm

    The patch is 5 ÷ 0.5 = 10 cm long. It is twice as long as the beam is wide.

Keep it

Copy this into your exercise book.

Climate: the pattern over about 30 years. It depends on latitude, height (6.5 °C colder for each km) and distance from the sea. Bars are rain, the line is temperature.

Draw: A climate graph: bars for rain, a line for temperature, a scale on each side, and the months along the bottom.

Reading with a child? A short page for the adult: what this chapter teaches and three questions to ask.

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