GeographyISC Class 11 · Atmospheric Temperature

Heating of the Atmosphere, Insolation and the Heat Budget (ISC Class 11 Geography)

Updated 17 October 2026 · Fact-checked

The atmosphere is heated mainly from below by radiation from the earth, then by conduction, convection and advection. Insolation depends on the angle of the sun's rays, duration of day and transparency of the air. Of 100 units of insolation, 35 are reflected (albedo), 14 absorbed by the air and 51 by the surface, and it all balances.

Understand Heating of the Atmosphere, Insolation and the Heat Budget

Heating and cooling. Short-wave solar radiation passes through air without heating it much; the earth absorbs it and warms the air. Radiation: the earth gives long-wave radiation absorbed by greenhouse gases, the main way the air is heated. Conduction: contact with the warm ground, affecting only the lowest layers. Convection: warm air rises and carries heat up. Advection: horizontal movement of air carries heat, for example the loo or land and sea breezes. Cooling: terrestrial radiation on clear nights, contact with cold surfaces, mixing and adiabatic expansion.

Insolation. The outer atmosphere receives about 1.94 calories per square centimetre per minute (about 1,360 watts per square metre). Factors: angle of the sun's rays (vertical rays concentrate energy and pass through less air; slanting rays spread it and lose more), duration of the day, and transparency of the air (clouds, vapour, dust). Cloudy equatorial areas receive less at the surface than clear subtropical deserts. The earth is nearest the sun about 3 January and farthest about 4 July, with little effect.

Heat budget (100 units). 35 reflected (27 clouds, 2 snow and ice, 6 scattering); 65 absorbed (14 atmosphere, 51 surface). The surface radiates 51: 17 direct to space, 34 absorbed by the atmosphere (6 direct, 9 convection and turbulence, 19 latent heat). The atmosphere radiates 14 + 34 = 48. Total to space = 17 + 48 = 65, balancing the 65 absorbed.

Latitudinal balance. Surplus between about 40 degrees N and 40 degrees S, deficit towards the poles; winds and ocean currents carry heat poleward.

Heating of the Atmosphere, Insolation and the Heat Budget: key facts

Heat budget (100 units): $R e f l ec t e d 35∣ A b sor b e d 65 = 14 a t m os p h er e + 51 s u r f a ce ∣ T os p a ce 17 + 48 = 65$
Heating modes: $R a d ia t i o n ∣ C o n d u c t i o n ∣ C o n v ec t i o n ∣ A d v ec t i o n$
Insolation factors: Angle of rays
Duration of day
Transparency of air
Latitudinal balance: Surplus 40 N to 40 S
Deficit towards poles
Winds and currents transfer heat

How to answer Heating of the Atmosphere, Insolation and the Heat Budget questions

Heat budget questions are 4 to 7 marks; always give units out of 100 and check the balance.

1Name each heating mode with one line.
2List insolation factors and explain why the poles receive less.
3Write the 100-unit budget in order: reflected, absorbed, radiated.
4Check that outgoing equals incoming.

Heating of the Atmosphere, Insolation and the Heat Budget 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.

Scaling the budget

Suppose a model uses 200 units of insolation in the same proportions.

Find units reflected, absorbed by atmosphere and by surface.

Try it first, then show the solutionSolution

Reflected = 35% of 200 = 70; absorbed = 130.
Atmosphere = 14/100 x 200 = 28; surface = 51/100 x 200 = 102.
Check: 70 + 28 + 102 = 200.

Answer: 70 reflected; 28 atmosphere; 102 surface.

Memory hook: Everything is doubled.

Slanting rays

Suppose a torch is shone straight down on a table, then at a low angle.

Which patch is brighter and how does this model latitude?

Try it first, then show the solutionSolution

Straight beam covers a smaller area, so energy per area is greater.
Low-angle beam spreads over more area, like polar regions.

Answer: The straight beam is brighter; poles receive slanting rays.

Memory hook: Straight is strong, slanting is weak.

Tricks to remember Heating of the Atmosphere, Insolation and the Heat Budget

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

35-14-51
35 bounced, 14 air, 51 ground: 100.
Use it when: Budget.
RCCA
Radiation, Conduction, Convection, Advection.
Use it when: Heating modes.

Heating of the Atmosphere, Insolation and the Heat Budget: solved examples

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

Example 1: Definition · 1 mark · MCQBoard level

The transfer of heat by the horizontal movement of air is:
(a) conduction
(b) convection
(c) advection
(d) radiation

Try it first, then show the solutionSolution

Horizontal.

Answer: (c) Advection.

Example 2: Albedo · 3 marks · Short answerBoard level

What is albedo and what percentage of insolation is reflected according to the heat budget? Name its three parts.

Try it first, then show the solutionSolution

Albedo is the share of insolation reflected to space.
35 units out of 100.
27 by clouds, 2 by snow and ice, 6 by scattering.

Answer: 35 per cent: 27 clouds, 2 snow and ice, 6 scattering.

Example 3: Budget sum · 4 marks · Long answerHarder board level

If the top of the atmosphere receives 250 units, find the units reflected, absorbed by the atmosphere, absorbed by the surface, and radiated directly to space by the earth's surface.

Try it first, then show the solutionSolution

Reflected = 0.35 x 250 = 87.5.
Atmosphere absorbs 0.14 x 250 = 35; surface absorbs 0.51 x 250 = 127.5.
Surface direct to space = 0.17 x 250 = 42.5.
Check: 87.5 + 35 + 127.5 = 250.

Answer: 87.5 reflected; 35 atmosphere; 127.5 surface; 42.5 direct to space.

Example 4: Why poles receive less · 4 marks · Long answerHarder board level

The Arctic has nearly continuous daylight in midsummer but stays cold. Explain how angle of rays, path through the air and surface reflection account for this.

Try it first, then show the solutionSolution

Slanting rays spread over a larger area.
They pass through more atmosphere, where more is absorbed and scattered.
Snow and ice reflect much of the rest.
Duration does not make up for the low angle.

Answer: Low sun angle and long path through air, plus snow albedo, outweigh day length.

Example 5: Heat transfer · 5 marks · Case-basedHOTS / competency

Case: Without winds and ocean currents, the tropics would get hotter and the poles colder. (a) Explain using surplus and deficit. (b) Name two transfer agents. (c) Give an example of advection in India.

Try it first, then show the solutionSolution

(a) Between 40 N and 40 S more heat is received than lost; poleward there is a deficit; unless transferred the imbalance would grow.
(b) Winds (including storms) and ocean currents.
(c) The loo, or land and sea breezes.

Answer: (a) Surplus in the tropics, deficit at the poles (b) winds and currents (c) the loo.

Where students lose marks in Heating of the Atmosphere, Insolation and the Heat Budget

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

Mistake: Writing that the atmosphere is heated directly by sunlight
Short-wave radiation passes through.
Do this: Say the earth is heated first and heats the air by long-wave radiation.
Usually costs: 2 marks.
Mistake: Budget not adding up
Units are misquoted.
Wrong working
Absorbed 14 + 35
Right working
Absorbed 14 + 51 = 65
Do this: Use 35, 14, 51 and 17 plus 48.
Usually costs: 1 to 2 marks.
Mistake: Ignoring day length
Only angle is given.
Do this: Mention angle, duration and transparency.
Usually costs: 1 mark.

Exam tips

Give the budget as 100 units.
Mention albedo with its three parts.
State long-wave versus short-wave.
Add one Indian advection example.

Practice questions on Heating of the Atmosphere, Insolation and the Heat Budget

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
Of 100 units of insolation, the units reflected back to space are:
(a) 14
(b) 35
(c) 51
(d) 65
Hint
Albedo.
Answer
(b) 35.
Q2 · 3 marks · Short answerHarder board level
The outer atmosphere receives 1.94 cal per cm2 per minute. Find the energy received per cm2 in one hour.
Hint
Multiply by 60.
Answer
1.94 x 60 = 116.4 cal per cm2 per hour.
Q3 · 4 marks · Long answerHarder board level
Explain how the atmosphere is heated mainly from below.
Hint
Short-wave passes, long-wave absorbed.
Answer
Solar short-wave radiation passes through air with little heating; the earth absorbs it and radiates long-wave heat which greenhouse gases absorb. Conduction and convection then carry heat upward.
Q4 · 3 marks · Short answerHarder board level
Show that the heat budget balances for 100 units by adding what is lost to space.
Hint
17 + 48.
Answer
Surface direct to space 17; atmosphere radiates 14 + 34 = 48; total 17 + 48 = 65, equal to 65 absorbed, plus 35 reflected making 100.
Q5 · 4 marks · Case-basedHOTS / competency
Case: A desert and an equatorial forest at the same latitude differ in surface insolation. (a) Which gets more? (b) Give the factor. (c) Explain it.
Hint
Transparency of the atmosphere.
Answer
(a) The desert. (b) Transparency of the atmosphere. (c) Clear desert air lets more reach the ground, while cloud and vapour in the forest reflect and absorb.

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.Units absorbed by surface?Show answer
51.
2.Units absorbed by atmosphere (insolation)?Show answer
14.
3.Solar constant in cal?Show answer
About 1.94 cal per cm2 per min.
4.Latitudes of surplus?Show answer
About 40 N to 40 S.
5.Perihelion date?Show answer
About 3 January.

Heating of the Atmosphere, Insolation and the Heat Budget: frequently asked questions

Why is air a poor conductor?

Conduction only affects the lowest layers.

Does earth heat up forever?

No, outgoing equals incoming over long periods.

What carries heat poleward?

Winds and ocean currents.