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Climate Change and Global Warming Class 11 Geography

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GeographyCBSE Class 11 · World Climate and Climate Change

Climate Change, the Greenhouse Effect and Global Warming (Class 11 Geography, Fundamentals of Physical Geography, Chapter 11)

Updated 17 October 2026 · Fact-checked

Climate change is natural and continuous; the present climate has prevailed for about 10,000 years. Evidence comes from glacial landforms, lake sediments, tree rings and records; causes include sunspots, Milankovitch cycles, volcanism and rising greenhouse gases (CO2, CFCs, methane, nitrous oxide, ozone) which cause global warming; the Kyoto Protocol set emission cuts.

Notice that greenhouse gases send part of the rising heat back to Earth, so more of these gases means more warming.

Illustration drawn for QuestionBuddy.

Understand Climate Change: Evidence, Natural and Human Causes, the Greenhouse Effect and Global Warming

Why this topic matters. Assessed through project and presentation; causes of climate change and the greenhouse effect are the most useful ideas to organise a project.

1. Natural and continuous change. Today's climate has prevailed for about 10,000 years with minor fluctuations. Evidence: geological records of alternating glacial and inter-glacial periods; landforms at high altitudes and latitudes showing glacier advances and retreats; sediments in glacial lakes; tree rings showing wet and dry periods; historical records of crop yields, floods and migrations.

2. Examples. The Rajasthan desert was wet and cool around 8,000 BC, rain was higher about 3,000 to 1,700 BC (the Harappan civilisation was at its centre in 2,000 to 1,700 BC) and conditions have been dry since. The last major glacial peak was about 18,000 years ago and the present inter-glacial began 10,000 years ago. Recent examples: the Sahel drought (1967-1977), the dust bowl of the US Great Plains in the 1930s, and the Little Ice Age in Europe (1550-1850).

3. Causes. (i) Astronomical: sunspots (dark, cooler patches rising and falling cyclically, with findings not statistically significant) and Milankovitch oscillations (cycles in the earth's orbit, wobble and axial tilt that change insolation). (ii) Volcanism: eruptions throw up aerosols that stay for long and reduce sunlight, so the earth's average temperature fell for some years after Pinatubo and El Chichon. (iii) Human: the rising concentration of greenhouse gases.

4. Greenhouse effect. The atmosphere transmits incoming short-wave solar radiation but absorbs most long-wave radiation from the earth. Gases that absorb it are greenhouse gases: carbon dioxide, CFCs, methane, nitrous oxide and ozone. The name comes from a glass greenhouse, transparent to short waves and opaque to long waves. A gas's effect depends on the rise in its concentration, its lifetime and the wavelength it absorbs.

5. Global warming. CO2 comes mainly from burning fossil fuels; forests and oceans are sinks; it is rising about 0.5 per cent a year. CFCs destroy stratospheric ozone, creating the ozone hole over Antarctica. The world's average near-surface temperature is about 14 degrees C and was about 0.6 degrees C higher at the end of the 20th century than at the end of the 19th. Effects include melting ice and thermal expansion raising sea level. The Kyoto Protocol (1997, in force 2005) set emission cuts.

Climate Change: Evidence, Natural and Human Causes, the Greenhouse Effect and Global Warming: key facts

Evidence of change
  • Glacial landforms
  • Lake sediments
  • Tree rings
  • Historical records
  • Geological record of glacial and inter-glacial periods
Natural and continuous.
Causes
Astronomicalsunspots, Milankovitch cycles
Terrestrialvolcanic aerosols
Humangreenhouse gases
Three groups.
Greenhouse gases
  • CO2
  • CFCs
  • Methane
  • Nitrous oxide
  • Ozone
Absorb long-wave radiation.
Numbers
  • Present climate about 10,000 years
  • CO2 up about 0.5 per cent a year
  • Average temperature about 14 degrees C
  • Rise about 0.6 degrees C in a century
Global warming.

How to answer Climate Change: Evidence, Natural and Human Causes, the Greenhouse Effect and Global Warming questions

Cause questions are answered by grouping.

  1. 1Name the group (astronomical, terrestrial, human).
  2. 2Give the process (cycles, aerosols, gas build-up).
  3. 3Add the chapter example (Pinatubo, Milankovitch).
  4. 4Link to the effect on temperature or radiation.

Climate Change: Evidence, Natural and Human Causes, the Greenhouse Effect and Global Warming 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.

Car in the sun

Suppose a closed car left in the sun becomes much hotter inside than outside.

Which idea does this illustrate?

Try it first, then show the solutionSolution
  1. Glass lets short-wave sunlight in but traps long-wave radiation.
  2. This is the greenhouse effect.

Answer: The greenhouse effect.

Memory hook: Glass in, heat trapped.

Ash cloud year

Suppose a major volcanic eruption throws a thick aerosol layer into the upper air and the next two summers are cooler.

Which cause of climate change is this?

Try it first, then show the solutionSolution
  1. Aerosols stay for long and reduce sunlight reaching the surface.
  2. This is volcanism.

Answer: Volcanic aerosols cooling the earth.

Memory hook: Ash blocks sun.

Tricks to remember Climate Change: Evidence, Natural and Human Causes, the Greenhouse Effect and Global Warming

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

  • Sun, Orbit, Volcano, Human

    Sunspots, Milankovitch cycles, volcanic aerosols, greenhouse gases

    Use it when: Causes.

  • 5 GHGs

    CO2, CFCs, methane, nitrous oxide, ozone

    Use it when: Greenhouse gases.

  • 1997 and 2005

    Kyoto adopted and in force

    Use it when: Dates.

Climate Change: Evidence, Natural and Human Causes, the Greenhouse Effect and Global Warming: solved examples

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

Example 1: Milankovitch · 1 mark · MCQBoard level

Cycles in the earth's orbit, wobble and axial tilt that alter insolation are called:
(A) Hadley oscillations
(B) Milankovitch oscillations
(C) ENSO
(D) Sunspot cycles

Try it first, then show the solutionSolution
  1. They are cycles in orbit, wobble and axial tilt (1 mark).

Answer: (B)

Example 2: Evidence of change · 2 marks · Very short answerBoard level

Name four types of evidence for climate change. (2 marks)

Try it first, then show the solutionSolution
  1. Glacial landforms and lake sediments (1 mark).
  2. Tree rings and historical records (1 mark).

Answer: Glacial landforms, sediments in glacial lakes, tree rings and historical records (and geological records).

Example 3: Greenhouse effect · 3 marks · Short answerHarder board level

Explain the greenhouse effect and name any three greenhouse gases. (3 marks)

Try it first, then show the solutionSolution
  1. The atmosphere transmits short-wave solar radiation but absorbs most long-wave terrestrial radiation (1 mark).
  2. This keeps the earth warmer, like glass in a greenhouse (1 mark).
  3. Gases: carbon dioxide, methane, CFCs, nitrous oxide, ozone (1 mark).

Answer: The atmosphere lets incoming short-wave solar radiation pass but absorbs most of the long-wave radiation emitted by the earth. This warming is the greenhouse effect, named after a glass greenhouse that is transparent to short waves and opaque to long waves. Greenhouse gases include carbon dioxide, methane and CFCs.

Example 4: Assertion and reason: volcanism · 1 mark · Assertion-reasonHarder board level

Assertion (A): Large volcanic eruptions can cool the earth for some years.
Reason (R): Aerosols thrown up stay in the air for long and reduce the sunlight reaching the surface.
(A) Both true, R explains A
(B) Both true, R does not explain A
(C) A true, R false
(D) A false, R true

Try it first, then show the solutionSolution
  1. Aerosols reduce sunlight, which explains the fall in temperature (1 mark).

Answer: (A)

Example 5: HOTS: CO2 growth · 5 marks · Long answerHOTS / competency

Carbon dioxide is rising by about 0.5 per cent a year. Starting from a concentration of 300 units, find the approximate value after 10 years (simple 0.5 per cent of the original each year and compounded), and discuss why the rise matters, naming two sources and two sinks. (5 marks)

Try it first, then show the solutionSolution
  1. Simple rise: 0.5 per cent of 300 = 1.5 units a year, 10 years = 15 units, giving 315 (1 mark).
  2. Compounded: 300 x 1.005^10 = about 315.3 (1 mark).
  3. The two methods agree closely at this rate (1 mark).
  4. Sources: burning of fossil fuels (and deforestation); sinks: forests and oceans (1 mark).
  5. It matters because CO2 absorbs long-wave radiation, so rising concentration strengthens the greenhouse effect (1 mark).

Answer: Simple rise: 0.5 per cent of 300 = 1.5 units a year, so after 10 years about 315 units. Compounded: 300 x 1.005^10 = about 315.3, almost the same. CO2 comes mainly from burning fossil fuels, while forests and oceans are sinks. The rise matters because CO2 absorbs long-wave terrestrial radiation, so a higher concentration strengthens the greenhouse effect and contributes to global warming.

Where students lose marks in Climate Change: Evidence, Natural and Human Causes, the Greenhouse Effect and Global Warming

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

  • Mistake: Saying ozone is not a greenhouse gas

    Ozone layer idea.

    Wrong working

    Ozone is only a protective gas.

    Right working

    Ozone is also a greenhouse gas; very effective in the lower troposphere.

    Do this: List five GHGs.

    Usually costs: 1 mark.

  • Mistake: Writing that climate change is only man-made

    One-sided.

    Wrong working

    All climate change is due to humans.

    Right working

    Change is natural and continuous; humans add greenhouse gases.

    Do this: Give both.

    Usually costs: 1 mark.

  • Mistake: Saying CO2 is a sink

    Terms reversed.

    Wrong working

    CO2 is a sink for forests.

    Right working

    Forests and oceans are sinks for CO2.

    Do this: Source versus sink.

    Usually costs: 1 mark.

Exam tips

  • Group the causes as astronomical, volcanic and human.
  • Quote 10,000 years, 0.5 per cent a year and 0.6 degrees C.
  • Link the greenhouse effect to glass and long-wave radiation.

Practice questions on Climate Change: Evidence, Natural and Human Causes, the Greenhouse Effect and Global Warming

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

  1. Q1 · 1 mark · MCQBoard level

    The Kyoto Protocol came into force in:
    (A) 1992
    (B) 1997
    (C) 2005
    (D) 2015

    Hint

    After the 1997 meeting.

    Answer

    (C)

  2. Q2 · 2 marks · Very short answerBoard level

    Name two natural causes of climate change. (2 marks)

    Hint

    Space and Earth.

    Answer

    Sunspot variation and Milankovitch cycles are astronomical causes; volcanic eruptions are a terrestrial cause.

  3. Q3 · 3 marks · Short answerHarder board level

    What are CFCs and what harm do they cause? (3 marks)

    Hint

    Ozone.

    Answer

    CFCs are chlorofluorocarbons, greenhouse gases that are highly effective at absorbing long-wave radiation. They also destroy ozone in the stratosphere, creating the ozone hole over Antarctica.

  4. Q4 · 3 marks · Short answerHarder board level

    State three pieces of evidence that the climate of Rajasthan has changed in the past. (3 marks)

    Hint

    8,000 BC.

    Answer

    The desert was wet and cool around 8,000 BC, rainfall was higher around 3,000 to 1,700 BC when the Harappan civilisation was at its centre in 2,000 to 1,700 BC, and conditions have been dry since.

  5. Q5 · 4 marks · Short answerHOTS / competency

    Why are sunspots an uncertain explanation of climate change? Give both the proposed link and the weakness, and compare with the volcanic cause. (4 marks)

    Hint

    Not statistically significant.

    Answer

    Sunspots are dark, cooler patches that rise and fall cyclically; some meteorologists link more sunspots with cooler, wetter, stormier weather and fewer with warmer, drier weather, but the findings are not statistically significant. Volcanism is better documented, since aerosols from eruptions such as Pinatubo and El Chichon reduced sunlight and lowered the average temperature for some years.

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. 1.How long has the present climate prevailed?Show answer

    About 10,000 years.

  2. 2.Which eruption cooled the earth?Show answer

    Pinatubo and El Chichon.

  3. 3.What destroys stratospheric ozone?Show answer

    CFCs.

  4. 4.Which two are CO2 sinks?Show answer

    Forests and oceans.

Climate Change: Evidence, Natural and Human Causes, the Greenhouse Effect and Global Warming: frequently asked questions

Is global warming the only climate change?

No; natural changes such as the Little Ice Age also occurred.

What is a greenhouse gas lifetime?

The time a gas stays in the atmosphere, affecting its warming effect.

Who set emission cuts?

The Kyoto Protocol, 1997.