Earth never runs a heat surplus or deficit for long. Every unit of energy it takes in from the Sun, it eventually gives back to space.
This balance, called the heat budget, is why the planet’s average temperature holds steady even as heat moves constantly between the ground, the air, and space.
MCQ Questions🏛️ Must Know
How the Atmosphere Gets Heated
- Conduction Heat passes directly between two things touching each other, like the ground warming the air right above it, until both reach the same temperature.(NCERT 11)
- Convection Warmed air near the ground rises as currents, carrying heat upward. This vertical transfer only happens within the troposphere.(NCERT 11)
- Advection Heat moves sideways, through horizontal air movement. In north India’s summer, the hot “loo” wind is a direct result of advection.(NCERT 11)
- Terrestrial Radiation The Sun heats the ground first, in short waves. The ground then re-radiates that heat as long waves, which is what actually warms the atmosphere.(NCERT 11)
Earth’s Heat Budget: The 100-Unit Balance
- Reflected First Of all incoming insolation, 35 units are reflected straight back to space before ever warming anything. This reflected share is called the Earth’s albedo.(NCERT 11)
- What Gets Absorbed The remaining 65 units are absorbed: 14 within the atmosphere itself, and 51 by the Earth’s surface directly.(NCERT 11)
- Sending It Back The Earth radiates its 51 units back out. Of these, 17 go directly to space, while 34 are re-absorbed by the atmosphere first.(NCERT 11)
- The Balance Adding it up: 17 units from the Earth plus 48 units radiated by the atmosphere equals 65, matching the 65 units absorbed in the first place. Nothing is lost or gained overall.(NCERT 11)
- Surplus and Deficit The zone between 40°N and 40°S has a net radiation surplus. The poles run a deficit instead, and winds carry the extra tropical heat poleward to balance it out.(NCERT 11)
📘 Good to Know
Insolation: Why It Varies
- Aphelion and Perihelion Earth is farthest from the Sun on 4 July (aphelion, 152 million km) and closest on 3 January (perihelion, 147 million km). This barely affects daily weather, though.(NCERT 11)
- Five Variability Factors How much insolation a place gets depends on Earth’s rotation, the sun’s angle of incidence, day length, atmospheric transparency, and land aspect.(NCERT 11)
- Why Scattering Colours the Sky Tiny particles in the troposphere scatter sunlight in all directions. That scattering is exactly why the sky looks blue, and sunrise and sunset look red.(NCERT 11)
What Controls Temperature
- Five Factors A place’s temperature depends on its latitude, altitude, distance from the sea, the air masses and ocean currents passing by, and local land aspect.(NCERT 11)
- Normal Lapse Rate Temperature normally drops about 6.5°C for every 1,000 metres of height gained. This is why hill stations stay cooler than the plains below them.(NCERT 11)
- Land vs Sea Land heats up and cools down fast. The sea does both slowly, so coastal places see far smaller temperature swings than places deep inland.(NCERT 11)
Test Yourself
🌟 Great to Know
Reading Temperature Maps
- Isotherms These are lines joining places with equal temperature. They generally run parallel to latitude lines, since latitude is temperature’s biggest driver.(NCERT 11)
- January’s Bending Isotherms In January, isotherms bend north over the North Atlantic Ocean, since warm currents like the Gulf Stream keep it milder. Over land, they bend south instead, as the land cools faster.(NCERT 11)
- Extreme Range The Siberian interior sees a temperature range of over 60°C between January and July, the largest anywhere. Near the equator, the range can be as small as 3°C all year.(NCERT 11)
Temperature Inversion
- What It Is Normally, temperature falls with height. In an inversion, this flips: temperature actually rises with height near the ground instead.(NCERT 11)
- When It Happens A long, clear, still winter night is the classic setup. The ground radiates its heat away all night, so by early morning it’s colder than the air just above it.(NCERT 11)
- Fog and Smoke Inversion traps smoke and dust in a stable layer near the ground, which is exactly why dense winter fog is so common in the early morning.(NCERT 11)
- Air Drainage In hills and valleys, cold night air flows downhill like water and pools in the valley floor. This protects crops on the upper slopes from frost damage.(NCERT 11)
📝 Exam Point of View
Exam Point of View: Lapse Rate and Inversion
- Real PYQ CAPF ACs 2022, General Ability asked which statement correctly describes the normal lapse rate. The answer: temperature is highest at ground level and falls with altitude.
- Real PYQ NDA & NA (I) 2026, General Ability tested three statements on temperature inversion. The trap: it named “cloudy” skies as the trigger, when it’s actually clear skies that let heat escape at night.
- Real PYQ UPSC CSP 2024, GS Paper I tested isotherm bending in January over the North Atlantic. The trap: the option claimed cold currents caused it, when the Gulf Stream and North Atlantic Drift are actually warm.
- The Pattern These questions reward reading each statement’s cause-and-effect claim carefully, not just recognising the vocabulary. A true term paired with a flipped cause is the standard trick.
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