---
title: "Short note: Global warming"
subject: "Engineering Chemistry"
chapter: 3
key: "semester_2/engineering_chemistry:global-warming-note"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/global-warming-note
site: BCT Engineering
---

# Short note: Global warming

Engineering Chemistry · Chapter 3: Environmental Chemistry

- Asked in: 2067 Mangsir, 3 marks
- Video: [How Does Global Warming Effect The Environment | Environmental Chemistry | Chemistry | FuseSchool](https://www.youtube.com/watch?v=4Uy9b87cYRs) — FuseSchool - Global Education
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/global-warming-note
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-3

## Question

Write a short note on global warming.

## Short answer

Global warming is the rise in Earth's average temperature due to increased greenhouse gases (CO2, CH4, N2O, CFCs) trapping infrared radiation. Main causes are fossil fuel combustion, deforestation, and agriculture. Consequences: melting ice, sea-level rise, climate extremes, crop loss, biodiversity decline. Remedies include renewable energy, afforestation, and emission controls.

## Answer

**Global warming** is the gradual rise of the average temperature of the earth's surface and lower atmosphere due to the increased concentration of greenhouse gases (CO₂, CH₄, N₂O, CFCs, water vapour, O₃). The rise has been about 1.1 °C since the pre-industrial era.

**Mechanism (greenhouse effect):** Short-wave solar radiation passes through the atmosphere and warms the earth. The earth re-emits this energy as long-wave infrared radiation. Greenhouse gases absorb part of this infrared and send it back towards the earth, so the lower atmosphere is warmer than it would otherwise be (greenhouse effect). Human activities add more of these gases, so the effect is enhanced.

```text
   Sun
    │ short-wave
    ▼
 ─────────────── GHG layer (CO₂, CH₄ ...)
    ▲     │ absorbs and returns IR
    │ IR  ▼
 =============== Earth surface (warms)
```

**Major gases:** CO₂ (fossil fuels, deforestation), CH₄ (paddy fields, cattle, landfills), N₂O (fertilisers), CFCs and tropospheric ozone.

**Consequences**
- Melting of glaciers and polar ice, and rise of sea level (flooding of coastal regions, island nations). In Nepal, Himalayan glaciers are retreating and glacial lake outburst floods are a threat.
- Changed rainfall patterns: more floods, droughts, storms and heat waves.
- Loss of crop yield, food and water shortage; shifting of climatic zones.
- Extinction of species and loss of biodiversity; coral bleaching.
- Spread of diseases such as malaria and dengue to new areas.

**Remedies**
- Reduce use of fossil fuels; use renewable energy (hydro, solar, wind), improve energy efficiency.
- Afforestation and stopping deforestation (trees absorb CO₂).
- Use public transport, electric vehicles and biogas.
- Control methane from landfills and agriculture; reduce use of nitrogen fertiliser.
- Stop using CFCs; follow international agreements: UNFCCC (1992), Kyoto Protocol (1997), Paris Agreement (2015).

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How do greenhouse gases cause the lower atmosphere to warm?
   A. They absorb part of the long-wave infrared re-emitted by the earth and send it back toward the earth
   B. They block short-wave solar radiation from reaching the earth
   C. They reflect all long-wave radiation into space
   D. They convert short-wave radiation into visible light
   Answer: A. Sunlight passes through, the earth re-emits long-wave IR, and greenhouse gases absorb part of it and return it toward the surface. (Key point: Greenhouse mechanism)

2. Which statement about the radiation involved in the greenhouse effect is correct?
   A. The earth re-emits short-wave radiation that gases absorb
   B. Solar radiation arrives as short-wave and the earth re-emits long-wave infrared
   C. Both incoming and outgoing radiation are long-wave
   D. Greenhouse gases emit short-wave radiation to the earth
   Answer: B. Short-wave solar radiation warms the earth, which re-emits the energy as long-wave infrared. (Key point: Radiation types)

3. Which pairing of gas and main source is correct?
   A. CO2 from fertilisers
   B. N2O from burning fossil fuels only
   C. CH4 from paddy fields, cattle and landfills
   D. CFCs from deforestation
   Answer: C. Methane comes from paddy fields, cattle and landfills; CO2 comes from fossil fuels and deforestation, and N2O from fertilisers. (Key point: Sources of gases)

4. Which measure helps reduce global warming according to the answer?
   A. Increasing nitrogen fertiliser use
   B. Clearing forests for farmland
   C. Increasing the use of CFCs
   D. Afforestation and use of renewable energy
   Answer: D. Trees absorb CO2 and renewable energy replaces fossil fuels, both lowering greenhouse gas levels. (Key point: Remedies)

## Related in Engineering Chemistry

- [Global warming: causes, consequences, remedies](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aglobal-warming) — Engineering Chemistry, chapter 3, asked 2×
- [Global warming: meaning, causes, consequences](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aglobal-warming-causes-consequences) — Engineering Chemistry, chapter 3

## Related in other subjects

- [Global warming and greenhouse gases](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Aglobal-warming-ghg-climate) — Energy Environment and Society, chapter 4
- [Research article on global warming](https://www.bctengineer.com/question.md?key=semester_5%2Fcommunication_english%3Aresearch-article-global-warming) — Communication English, chapter 10
- [Global warming and international efforts](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Aglobal-warming-international) — Technology, Environment and Society, chapter 6