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Greenhouse Effect, Climate and Mitigation

Use atmospheric evidence to explain infrared heat trapping, climate consequences and mitigation choices.

  • SEC G3 Pure Chemistry 2027
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Learning objectives

  • state that carbon dioxide and methane are greenhouse gases and may contribute to global warming; give the sources of these gases and describe the potential effects of increased levels of these greenhouse gases, including more extreme weather events and melting of polar ice.

Outcome: interpret greenhouse-gas evidence, explain the infrared mechanism and evaluate a response at the correct causal point. Prerequisite: Carbon Cycle and combustion from Fossil Fuels.

1. Definition

A greenhouse gas absorbs and re-emits infrared radiation emitted by Earth. The natural greenhouse effect keeps Earth warmer than it would otherwise be. The enhanced greenhouse effect is the additional heat retention caused by increased greenhouse-gas concentrations; global warming is the associated long-term rise in Earth’s average temperature.

2. Key Ideas

Carbon dioxide and methane are required examples. Increasing their concentration can reduce heat loss to space and enhance the natural effect. Responses can reduce emissions or increase carbon removal; they do not “turn off” the natural greenhouse effect.

Retrieval check
Which carbon-cycle process removes atmospheric carbon dioxide? Photosynthesis.

3. Detailed Explanations

Greenhouse gases reduce infrared heat loss from EarthSunlight passes through the atmosphere and warms Earth. Earth emits infrared radiation upward. Greenhouse gases absorb some infrared radiation and re-emit it in different directions; some escapes to space and some returns toward the surface.Enhanced greenhouse effect: more IR is retainedSunAtmosphere: CO₂ and CH₄ absorb infraredGreenhouse gases re-emit IR in different directions.Earth's surfacesunlightIR from Earthsome IR escapessome IR returns
Earth emits infrared radiation. Greenhouse gases absorb and re-emit some of it, reducing heat loss to space.

Real monitoring data provide evidence of atmospheric change:

YearMauna Loa annual mean CO₂ / ppm
1960316.9
2000369.7
2020414.2

Source: NOAA Global Monitoring Laboratory Mauna Loa annual means, rounded. The table shows concentration change; it does not by itself prove every consequence. The mechanism supplies the causal explanation:

more greenhouse-gas molecules → more outgoing infrared absorbed and re-emitted → less heat escapes to space → average temperature rises.

Possible consequences include sea-level rise, coastal flooding, altered rainfall and habitat disruption. Responses include reducing fossil-fuel combustion, limiting methane leakage and protecting carbon sinks. The fuel families remain owned by Energetics and Organic Chemistry.

Do not merge three different mechanisms. Greenhouse warming changes infrared energy transfer; acid rain lowers environmental pH after sulfur dioxide or nitrogen oxides form acidic substances; ozone depletion reduces stratospheric protection from ultraviolet radiation.

4. Common Mistakes

  • Greenhouse gases change energy transfer; they do not create energy.
  • The mechanism uses infrared, not ultraviolet radiation.
  • The natural greenhouse effect is necessary; increased greenhouse-gas concentrations enhance it.
  • Acid rain and ozone depletion have different precursors, mechanisms and effects from greenhouse warming.
  • One weather event is not the same as a long-term climate trend.
  • Mitigation reduces causes; adaptation reduces harm from consequences.

5. Exam Tips

Separate evidence (the trend in the table) from mechanism (infrared absorption and reduced heat loss) and from consequence (a named climate risk).

6. Worked Examples

Modelled example 1

Model: use the source table

Core

Problem

Describe the 1960–2020 trend and explain how it can contribute to warming.
Study the worked solution

  1. Describe

    Method

    Carbon dioxide rises from about 316.9 ppm to 414.2 ppm.

    Reason

    Quote both endpoints and direction.

    Working

    increase ≈ 97.3 ppm.

  2. Explain

    Method

    More CO₂ absorbs and re-emits more outgoing infrared.

    Reason

    Less heat escapes to space.

    Working

    higher concentration → enhanced greenhouse effect → higher average temperature.

Guided practice 2

Guided: changed gas

About 4 min

Problem

A landfill captures methane before release. Which causal step is reduced?

Try this before viewing the solution

Reduced step

Hints

Hint 1: match gas and radiation
Decide whether methane belongs to the greenhouse infrared mechanism or the ozone ultraviolet mechanism.
View solution step by step

  1. Match gas to radiation

    Method

    Select infrared absorption.

    Reason

    Methane is a greenhouse gas, not the ozone layer.

    Working

    less CH₄ emitted → weaker added IR trapping.

Challenge 3

Transfer: classify two responses

Minimal support

Problem

Compare preventing methane leakage with building a sea wall.

Try this before viewing the solution

Classification

Hints

Hint 1: locate each response
Ask whether each action reduces the cause of warming or reduces harm from an effect.
View complete solution

  1. Locate each response

    Method

    Leak prevention is mitigation; the sea wall is adaptation.

    Reason

    One reduces a greenhouse-gas source; the other reduces flooding harm.

    Working

    cause control versus consequence control.

7. Mind Stretchers

Independent: A student says the table proves every place will receive less rainfall. Evaluate this conclusion.

Show answer
The table supports an increase in atmospheric carbon dioxide, not one identical local rainfall outcome. Climate consequences vary by region; the greenhouse mechanism supports warming risk but not that absolute prediction.

8. Quiz

Practise this lesson
Start focused practice, then continue to Ozone Layer and Depletion.