Good Learning Co.
SavannahYear 8
← Geography
GeographyWeather, climate and a warming world25 min★★★ difficulty

Global atmospheric circulation and why deserts sit where they do

Look at a world map of deserts. The Sahara, Arabian, Thar, Kalahari and Australian deserts all sit at roughly the same latitude on both sides of the equator. That is not a coincidence: it is the atmosphere's plumbing.

Part of your national curriculum
  • Locational knowledge: Extend locational knowledge and deepen spatial awareness of the world's countries, focusing on Africa, Russia, Asia and the Middle East
  • Human and physical geography: Understand weather and climate, including the change in climate from the Ice Age to the present

Lesson overview

What you'll learn in this lesson

Explain how circulation cells create the world's climate belts.

Key learning points

  • • The engine: unequal heating
  • • The three cells
  • • Pressure and wind, in one rule
  • • Why the UK's weather is so changeable

This lesson at a glance

  • 25 minutes
  • 16 parts to scroll through
  • 4 quick checks
  • Marked quiz at the end
  • Gentle pace: short sittings with pauses

Words to know

circulationcreateclimateengineunequal

Scroll down — the lesson carries on below

Part 1 of 16 · Discover6%
1

Watch & discover

Part 1 of 16

Watch first

Global atmospheric circulation and why deserts sit where they do

An English teaching video on this topic from iNewittAll. Watch it, then scroll down for the lesson.

In a nutshell

Explain how circulation cells create the world's climate belts.

2

Learning cycle

Part 2 of 16

Learning cycle 1 of 2

Part 1 · The engine: unequal heating

A short piece of teaching, then a check to make sure it has landed.

3

Explore the idea

Part 3 of 16

Learn

The engine: unequal heating

The Sun's rays hit the equator almost vertically, concentrating energy on a small area. At the poles the same beam spreads across a wider area and passes through more atmosphere, so it delivers less energy. This surplus at the equator and deficit at the poles drives air and ocean movement that constantly tries, and fails, to even the difference out.

4

Explore the idea

Part 4 of 16

Learn

The three cells

Hot air rises at the equator, cools, condenses and falls as heavy rain: the low pressure of the tropical rainforest belt. That air travels aloft to about 30 degrees north and south, where it sinks. Sinking air warms and dries, creating high pressure, clear skies and desert. Some of it returns to the equator as trade winds, completing the Hadley cell. The Ferrel and Polar cells repeat the pattern further north, giving wet, unsettled weather around 60 degrees and cold desert at the poles.

5

Quick check

Part 5 of 16

Quick check

Rising air at the equator produces

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Quick check

Part 6 of 16

Quick check

Which cell links the equator and 30 degrees?

7

Reset break

Part 7 of 16

Pause

That's sitting 1 of 2 done

Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.

Stop here for now
8

Learning cycle

Part 8 of 16

Learning cycle 2 of 2

Part 2 · Pressure and wind, in one rule

A short piece of teaching, then a check to make sure it has landed.

9

Explore the idea

Part 9 of 16

Learn

Pressure and wind, in one rule

Rising air means low pressure, cloud and rain. Sinking air means high pressure, clear skies and dry weather. Wind blows from high to low pressure, and the Earth's rotation deflects it (the Coriolis effect), which is why trade winds blow from the north east in the northern hemisphere rather than straight south.

10

Explore the idea

Part 10 of 16

Learn

Why the UK's weather is so changeable

The UK sits near 55 degrees north, where warm tropical air meets cold polar air along the polar front. Depressions form on that boundary and are steered across us by the jet stream, so we get a rapid sequence of warm and cold fronts, showers and clear spells within days. The North Atlantic Drift also carries warm water north west, which is why Britain is far milder than Newfoundland at the same latitude.

11

Quick check

Part 11 of 16

Quick check

Why is the UK milder than places at the same latitude in Canada?

12

Quick check

Part 12 of 16

Quick check

Sinking air is dry because

13

Explore the idea

Part 13 of 16

Worked example

Worked answer: explain why hot deserts are found at about 30 degrees north and south (4 marks)

Air that rose at the equator has already lost its moisture as rainfall there (1). It travels polewards at high altitude, cools, becomes denser and sinks at around 30 degrees (1). Sinking air warms as it compresses, so its capacity to hold water vapour increases and clouds cannot form (1). This gives persistent high pressure, clear skies and very low rainfall, which is the definition of a hot desert climate (1).

14

Challenge round

Part 14 of 16

Game · Sort it

Which of these are true?

Drag each card into the right column. Tap a card first if dragging is fiddly.

True

Not true

15

Mastery quiz

Part 15 of 16

Marked quiz

End of lesson quiz: Global atmospheric circulation and why deserts sit where they do

4 questions, marked with the reasoning shown. No timer.

  1. 1. Which piece of evidence best supports the claim that recent warming is human-caused?

  2. 2. Rising air at the equator produces

  3. 3. Which cell links the equator and 30 degrees?

  4. 4. Why is the UK milder than places at the same latitude in Canada?

16

Lesson round-up

Part 16 of 16

Lesson round-up

Ready when you are

Quiz score

Not sat

Games

Not played

Points this lesson

0

Best run

0 in a row

Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?

Ask Luna

Do the work

Your written work for this lesson

This is the part you'd do in your book at school. Pick the pieces below, write here or on paper, and photograph anything you draw or work out.

Case study

Flooding on the River Calder

The town of Harbrook sits where a steep valley opens onto a flat floodplain. In December 2015, 120 mm of rain fell in 36 hours onto ground that was already saturated. The river rose 2.4 m in five hours, and 380 homes and 54 businesses flooded. Two roads and the railway closed for eleven days.

Geographers pointed to physical causes — steep slopes, impermeable rock, heavy rainfall — and human causes: moorland drained upstream, new housing built on the floodplain, and drains designed for smaller storms.

Since then the town has planted 40 hectares of woodland upstream, built leaky dams in small streams, and raised flood walls to 1.8 m. In the storm of 2020 the peak river level was 0.3 m lower and 40 homes flooded, not 380.

Written for Good Learning Co.

Reading questions

  1. List two physical and two human causes of the 2015 flood.
  2. Explain how planting woodland upstream lowers the river's peak level.
  3. Using the figures, judge how successful the scheme has been. Quote data in your answer.

  • Case study notes

    Writing

    Write the place, the facts and the figures from this lesson so you can revise them later.

    Half a page

  • Explain answer

    Writing

    Answer in full sentences, giving causes and effects. Use one figure or place name as evidence.

    8–10 sentences

  • Map or sketch

    Diagram

    Draw the map, cross-section or field sketch with a key, title and labels, then photograph it.

    1 map with a key

  • Data work

    Working out

    Plot your figures as a graph on paper and write one sentence about the pattern.

    1 graph + 1 sentence

Saved as you type.

Part 1 of 16 · Watch & discover

How this is going

  • Not looked at yet

    Extend locational knowledge and deepen spatial awareness of the world's countries, focusing on Africa, Russia, Asia and the Middle East

  • Not looked at yet

    Understand weather and climate, including the change in climate from the Ice Age to the present

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