---
title: "Global warming and greenhouse gases"
subject: "Energy Environment and Society"
chapter: 4
key: "semester_7/energy_environment_and_society:global-warming-ghg-climate"
source: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/global-warming-ghg-climate
site: BCT Engineering
---

# Global warming and greenhouse gases

Energy Environment and Society · Chapter 4: Environmental Impact of Energy sources

- Asked in: 2071 Shrawan, 2 marks; year not given
- Video: [Greenhouse Effect and Global Warming | Environmental Science | LetsTute](https://www.youtube.com/watch?v=d7Ci_EooW-k) — Let'stute
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/global-warming-ghg-climate
- Whole chapter: https://www.bctengineer.com/md/semester_7/energy_environment_and_society/chapter-4

## Question

Write a short note on global warming. What are greenhouse gases and what are the effects of climate change? Describe in brief.

## Short answer

Global warming is the long-term rise in Earth's average temperature due to increased greenhouse gases from human activities. Key GHGs are CO₂, CH₄, N₂O, and CFCs. Effects include rising temperatures, glacier melt, sea level rise, extreme weather, threats to agriculture, biodiversity loss, and health impacts.

## Answer

#### Global warming
**Global warming** is the long-term rise in the average temperature of the earth's atmosphere and oceans caused mainly by human activity that increases greenhouse gases. The earth has warmed by about 1.2–1.3 °C compared with pre-industrial (1850–1900) levels, and 2024 was the first calendar year more than 1.5 °C above that level (WMO and Copernicus). The cause is the enhanced greenhouse effect: gases trap outgoing infrared radiation from the earth.

```text
 Sun --> short-wave --> Earth surface
 Earth --> infrared --> [GHG layer] --> trapped,
                         re-radiated down => warming
```

#### Greenhouse gases (GHGs)
Gases that absorb infrared radiation and warm the atmosphere:
| Gas | Main source | GWP (100 yr, approx.) |
|---|---|---|
| Carbon dioxide (CO₂) | Burning fossil fuels, deforestation, cement | 1 |
| Methane (CH₄) | Livestock, rice paddies, landfill, gas leaks | 28 |
| Nitrous oxide (N₂O) | Fertiliser, burning | 265 |
| CFCs / HFCs | Refrigerants, aerosols | 1,000–10,000+ |
| SF₆ | Electrical switchgear | 23,500 |
| Water vapour, ozone | Natural / secondary | - |

#### Effects of climate change
- Rising temperatures and heat waves.
- Melting of glaciers and ice caps: Himalayan glaciers retreat fast, causing GLOF risk and, in the long run, reduced river flow that affects hydropower.
- Sea level rise, flooding of coastal areas.
- Changing rainfall: more floods, landslides and droughts (Nepal has seen extreme monsoon events).
- Threat to agriculture, food and water security.
- Loss of biodiversity and changes in ecosystems; ocean acidification.
- Health effects: vector-borne diseases, heat stress.
- Economic loss and migration.

## Check yourself

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

1. How do greenhouse gases cause warming?
   A. They absorb outgoing infrared radiation and re-radiate it downward
   B. They block incoming sunlight
   C. They absorb ultraviolet in the ozone layer
   D. They cool the surface by reflection
   Answer: A. The enhanced greenhouse effect traps infrared radiation from the earth. (Key point: Greenhouse effect)

2. Which gas has the highest GWP among these?
   A. CO2
   B. SF6
   C. CH4
   D. N2O
   Answer: B. SF6 has GWP about 23,500; CO2 is 1, CH4 28 and N2O 265. (Key point: GWP)

3. What is a climate-change effect on Himalayan glaciers relevant to Nepal?
   A. Growth of glaciers
   B. More hydropower in the long run always
   C. Fast retreat, GLOF risk and long-run reduced river flow affecting hydropower
   D. No change in river flow
   Answer: C. Glacial melt increases GLOF risk and eventually reduces river flow. (Key point: Glacier effects)

## Related in Energy Environment and Society

- [Biogas routes and climate change](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Abiogas-routes-climate-change) — Energy Environment and Society, chapter 3
- [Climate change and renewable mitigation](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Aclimate-change-renewables-mitigation) — Energy Environment and Society, chapter 4

## Related in other subjects

- [Greenhouse gases, effects and CO2-equivalent calculation](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Agreenhouse-gases-causes-effects-co2e) — Environment and Pollution Control, chapter 7
- [Greenhouse gases and global control efforts](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Agreenhouse-gases-efforts) — Engineering Chemistry, chapter 3
- [Climate change gases and symptoms in Nepal](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Acc-gases-symptoms-nepal) — Technology, Environment and Society, chapter 6
- [Climate change gases, impact and mitigation](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Acc-gases-impact-mitigation) — Technology, Environment and Society, chapter 6