GeographyICSE Class 9 · Insolation

Insolation and the Factors Affecting Temperature (ICSE Class 9 Geography)

Updated 17 October 2026 · Draft, not yet fact-checked

Insolation is the incoming solar radiation received by the earth, mainly as short waves. The earth's surface absorbs it and gives out heat as long-wave terrestrial radiation, which warms the atmosphere. Temperature depends on latitude, altitude, distance from the sea, slope, winds and ocean currents.

Notice that short waves pass through air to heat the ground, and the ground's long waves then warm the atmosphere from below.

Illustration drawn for QuestionBuddy.

Understand Insolation and the Factors Affecting Temperature

1. Insolation and terrestrial radiation. Insolation (incoming solar radiation) reaches the earth as short waves. A part is reflected back by clouds, dust and the surface (albedo); a part is absorbed by the atmosphere; roughly half reaches and heats the surface (a rounded statement). The heated earth gives out *terrestrial radiation* as long waves, which the atmosphere absorbs.

2. Heating of the atmosphere. Atmosphere is heated mainly from below. Processes: *radiation*, *conduction* (air touching the warm ground), *convection* (warm air rising) and *advection* (horizontal movement of air, as winds).

3. Latitude. The sun's rays are vertical near the equator and slant towards the poles. Slanting rays spread over a larger area and pass through more atmosphere, so temperature falls from the equator to the poles.

4. Altitude. Temperature falls about 6.5 degrees C per 1,000 m; thin air holds less heat. Hills are cooler than plains at the same latitude.

5. Distance from the sea. Water heats and cools slowly; land quickly. Coastal places have a *maritime* climate with a small annual range; interior places have a *continental* climate with hot summers, cold winters and a large range.

6. Slope, winds and ocean currents. Slopes facing the sun are warmer than those away. Warm winds raise and cold winds lower temperature. Warm currents warm coasts, cold currents cool them.

Insolation and the Factors Affecting Temperature: key facts

Radiation: Insolation: short waves | Terrestrial radiation: long waves
Heating: $R a d ia t i o n ∣ C o n d u c t i o n ∣ C o n v ec t i o n ∣ A d v ec t i o n$
Factors: Latitude
Altitude
Distance from sea
Slope
Winds
Ocean currents
Rates: $F a l l o f 6.5 d e g r ees C p er 1, 000 m ∣ R an g e = hi g h es t - l o w es t m e an$

Insolation and the Factors Affecting Temperature in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Two cities, same latitude

Suppose city P lies at sea level near the coast and city Q lies inland at 1,500 m at the same latitude.

Compare their temperatures.

Try it first, then show the solutionSolution

Q is cooler by about 6.5 x 1.5 = 9.75 degrees C due to altitude.
P has a small range because of the sea; Q has a larger range.

Answer: Q is cooler and has a larger annual range.

Memory hook: Higher and farther: cooler, wider range.

Tricks to remember Insolation and the Factors Affecting Temperature

Short memory aids. Say each one aloud once, then use it on a question the same day.

In-short
Insolation: incoming short waves.
Use it when: Meaning.
LAD-SWC
Latitude, Altitude, Distance from sea, Slope, Winds, Currents.
Use it when: Factors.

Insolation and the Factors Affecting Temperature: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Define · 2 marks · Short answerBoard level

Define insolation and terrestrial radiation. [2]

Try it first, then show the solutionSolution

Insolation is the solar radiation received by the earth.
Terrestrial radiation is heat given out by the earth.

Answer: Insolation is incoming solar radiation; terrestrial radiation is outgoing heat from the earth.

Example 2: Altitude · 3 marks · Short answerHarder board level

A town is at 2,400 m and a nearby plain at sea level is at 30 degrees C. Estimate the town's temperature and give a reason. [3]

Try it first, then show the solutionSolution

Fall = 6.5 x 2.4 = 15.6 degrees C.
Temperature = 30 - 15.6 = 14.4 degrees C.
Thin air holds less heat.

Answer: About 14.4 degrees C.

Example 3: Maritime vs continental · 4 marks · Long answerHarder board level

Explain with data why Mumbai has a smaller annual range than Delhi, given that the highest and lowest mean monthly temperatures are 33 and 24 degrees C for Mumbai and 41 and 14 degrees C for Delhi (illustrative figures). [4]

Try it first, then show the solutionSolution

Mumbai range = 33 - 24 = 9 degrees C.
Delhi range = 41 - 14 = 27 degrees C.
Mumbai is coastal, and the sea moderates temperature.
Delhi is inland, so land extremes occur.

Answer: Mumbai 9 degrees C (maritime); Delhi 27 degrees C (continental).

Example 4: Why slants · 3 marks · Short answerHarder board level

Why are polar regions cold even though the sun shines for months in summer? [3]

Try it first, then show the solutionSolution

Rays are very slanting.
They spread over a large area and travel through more atmosphere.
Ice reflects much of it (high albedo).

Answer: Slanting rays, large area and reflection by ice keep poles cold.

Example 5: Case: warm current · 5 marks · Case-basedHOTS / competency

Case. Two ports lie at 60 degrees N: one on the west coast of Europe and one on the east coast of Canada. The first remains ice-free in winter. (i) Name the warm current. [1] (ii) The cold current near Canada. [1] (iii) Explain the difference. [2] (iv) Name the factor involved. [1]

Try it first, then show the solutionSolution

(i) North Atlantic Drift.
(ii) Labrador Current.
(iii) The warm drift warms Europe; the cold current cools Canada.
(iv) Ocean currents.

Answer: (i) North Atlantic Drift (ii) Labrador Current (iii) Warm versus cold water (iv) Ocean currents.

Where students lose marks in Insolation and the Factors Affecting Temperature

The slips examiners see most often, and what to write instead.

Mistake: Writing that the atmosphere is heated directly by the sun
Heating from below is ignored.
Do this: Insolation heats the earth first; the earth heats the air.
Usually costs: 1 mark.
Mistake: Forgetting to convert height to thousands of metres
Wrong lapse rate use.
Do this: 6.5 per 1,000 m.
Usually costs: 1 mark.
Mistake: Mixing maritime and continental
Reversal.
Do this: Maritime: small range, continental: large range.
Usually costs: 1 mark.

Exam tips

Show the arithmetic for lapse rate and annual range.
Name the factor, then explain its effect.
Use maritime and continental terms.
Include the unit degrees C.

Practice questions on Insolation and the Factors Affecting Temperature

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Which heats the atmosphere mainly?
(a) Insolation directly
(b) Terrestrial radiation
(c) Moonlight
(d) Volcanoes
Hint
From below.
Answer
(b) Terrestrial radiation.
Q2 · 2 marks · Very short answerBoard level
Name two factors that affect temperature. [2]
Hint
Latitude.
Answer
Latitude and altitude.
Q3 · 1 mark · Very short answerBoard level
What is advection? [1]
Hint
Horizontal.
Answer
Horizontal movement of air carrying heat.
Q4 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Coastal areas have a smaller range of temperature.
Reason (R): Water heats and cools more slowly than land.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Specific heat.
Answer
(a).
Q5 · 3 marks · Short answerHarder board level
Explain why a hill station is cooler than the plain below. [3]
Hint
Altitude.
Answer
Temperature falls with height at 6.5 degrees C per 1,000 m and thin air holds less heat.
Q6 · 3 marks · Short answerHarder board level
Why does the south-facing slope of a northern hemisphere hill have warmer vegetation? [3]
Hint
Slope.
Answer
It faces the sun and receives more direct rays than the shaded north-facing slope.
Q7 · 3 marks · Short answerHarder board level
Describe the role of clouds in insolation and terrestrial radiation. [3]
Hint
Reflect/trap.
Answer
Clouds reflect part of insolation by day and trap terrestrial radiation at night, moderating temperature.
Q8 · 2 marks · Very short answerBoard level
What is albedo? Which surface has the higher albedo, fresh snow or a forest? [2]
Hint
Reflectivity.
Answer
Albedo is the fraction of radiation reflected; fresh snow has a higher albedo.
Q9 · 4 marks · Case-basedHOTS / competency
Case. Two stations A and B at the same height and latitude: A has an annual range of 8 degrees C, B has 31 degrees C. (i) Which is coastal? [1] (ii) Which has a continental climate? [1] (iii) Give two reasons. [2]
Hint
Range.
Answer
(i) A. (ii) B. (iii) The sea moderates A; B is far inland, so land heats and cools rapidly.
Q10 · 3 marks · Long answerHOTS / competency
Case. A student places a thermometer on grass and another on bare concrete at noon and finds different readings. Suggest the reason and what factor of climate it illustrates. [3]
Hint
Surface.
Answer
Different surfaces absorb and reflect differently; concrete absorbs more heat, so it is hotter, showing how the nature of the surface affects temperature.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Insolation means?Show answer
Incoming solar radiation.
2.Lapse rate?Show answer
6.5 degrees C per 1,000 m.
3.Process of vertical heat transfer?Show answer
Convection.
4.Which has a larger range, coast or interior?Show answer
Interior.
5.Warm current in the north Atlantic?Show answer
North Atlantic Drift.

Insolation and the Factors Affecting Temperature: frequently asked questions

Why is the equator hot?

Rays are almost vertical.

What is conduction?

Heat transfer by contact.

Does the sun heat air directly?

Mostly the earth does.