Greenhouse Effect and Global Warming
NCERT Class 12 • Biology • Chapter "Environmental Issues" | NCERT Class 9 • Science • Chapter "Natural Resources"
Greenhouse Effect and Global Warming
The greenhouse effect is natural and necessary. Certain gases in the atmosphere let sunlight through but trap the heat radiated back from the earth, which keeps the planet warm enough for life. The problem is not the effect itself but its intensification by human activity.
The Greenhouse Gases
- Without the natural greenhouse effect the earth's average temperature would be far below freezing, so life as we know it would be impossible.
- Carbon dioxide is the main greenhouse gas by quantity and comes from burning fossil fuel, deforestation and cement making.
- Methane comes from paddy fields, livestock, landfills and natural gas leaks, and is far more potent per molecule than carbon dioxide.
- Nitrous oxide comes mainly from nitrogen fertiliser and industry.
- Chlorofluorocarbons were used in refrigeration and aerosols and act both as greenhouse gases and as ozone destroyers.
- Water vapour is also a greenhouse gas, and warming increases it, which amplifies the original warming.
- Global warming is the rise in the average temperature of the earth caused by the accumulation of these gases.
Effects and Response
- Melting of glaciers and polar ice raises sea level and threatens low lying coasts and island nations.
- Changed rainfall patterns bring more intense downpours in some places and longer droughts in others.
- Extreme weather events such as heat waves, cyclones and floods become more frequent and more severe.
- Agriculture is affected because crops are tuned to a particular temperature and rainfall pattern.
- Species shift their ranges towards the poles and to higher altitudes, and those that cannot move fast enough decline.
- Mitigation means reducing emissions through renewable energy, energy efficiency, afforestation and less wasteful consumption.
- Adaptation means preparing for changes already under way, through flood defences, drought resistant crops and early warning systems.
| Gas | Main Source | Note |
|---|---|---|
| Carbon dioxide | Fossil fuel, deforestation | Largest by quantity |
| Methane | Paddy fields, livestock, landfill | More potent per molecule |
| Nitrous oxide | Fertiliser, industry | Long lived in the atmosphere |
| Chlorofluorocarbons | Refrigeration, aerosols | Also destroy ozone |
Greenhouse effect — the trapping of heat radiated from the earth by gases in the atmosphere, which keeps the planet warm.
Hindi me samjhein
ग्रीनहाउस प्रभाव स्वयं आवश्यक है, क्योंकि उसके बिना पृथ्वी बहुत ठंडी होती। समस्या यह है कि मानवीय गतिविधि ने उसे बहुत तीव्र कर दिया, जिससे वैश्विक तापन हो रहा है।
Exam me kaise aata hai
- The main greenhouse gas by quantity is — carbon dioxide
- Which gas comes largely from paddy fields and livestock — methane
- Reducing emissions is called — mitigation
- Preparing for changes already under way is called — adaptation
UPSC/State PSC ke liye
- Water vapour creates a feedback loop: warming raises evaporation, more vapour traps more heat, and the warming increases further.
- Mitigation and adaptation are not alternatives; some change is already locked in, so adaptation is needed even while emissions are cut.
Yahan confuse hote hain
✗ The greenhouse effect is entirely harmful | The natural effect is essential; its intensification is the problem | ✓
✗ Global warming and ozone depletion are the same | Warming comes from greenhouse gases; ozone depletion from ozone destroying chemicals | ✓
✗ Methane is unimportant because there is less of it | Methane is far more potent per molecule | ✓
Ek nazar me
- The natural greenhouse effect keeps the earth warm enough for life.
- Carbon dioxide, methane, nitrous oxide and chlorofluorocarbons intensify it.
- Effects include sea level rise, changed rainfall and extreme weather.
- The response combines mitigation of emissions with adaptation to change.