Greenhouse gases and global warming

Core concept

The natural greenhouse effect occurs when atmospheric gases absorb and re-emit outgoing infrared radiation. It keeps Earth habitable. Global warming is the long-term rise in average surface temperature caused mainly by the enhanced greenhouse effect from human activity; climate change is broader and includes rainfall, oceans, ice, extreme events and ecosystems.

Gases and sources

• Carbon dioxide (CO2): fossil fuels, cement, deforestation and land-use change. It is the largest contributor to cumulative anthropogenic warming and persists for a long time.
• Methane (CH4): livestock, rice cultivation, landfills, coal and oil-gas operations. It is shorter-lived than CO2 but has much higher warming potential per unit mass over standard assessment periods.
• Nitrous oxide (N2O): nitrogen fertilisers, manure and combustion; it also contributes to stratospheric ozone depletion.
• Fluorinated gases: HFCs, PFCs, SF6 and NF3 from refrigeration, industry and electronics. Their concentrations are small but their warming potential may be very high.
• Water vapour is abundant, but mainly a feedback: warmer air holds more moisture. It is not normally treated as the main human-controlled forcing.

Forcing and feedbacks

Positive radiative forcing adds energy to the Earth system; negative forcing cools it. Aerosols may scatter sunlight and cool, while black carbon absorbs radiation and darkens snow. Ice-albedo and water-vapour feedbacks amplify warming. Oceans absorb excess heat and CO2, causing ocean warming and acidification. Forests can act as carbon sinks, but fires, drought and deforestation weaken that service.

Indian examples

India faces heat waves, irregular monsoon rainfall, Himalayan snow and glacier changes, sea-level rise and risks to farming and health. Concrete-heavy cities with little vegetation create urban heat islands. Methane from flooded rice fields and ruminants shows why mitigation must include agriculture, not only power generation. Adaptation reduces vulnerability; mitigation reduces emissions or increases removals.

Exam tips

Do not confuse ozone depletion with global warming: ozone loss is chiefly linked to ozone-depleting chemicals, while warming is driven by enhanced greenhouse gases. Distinguish atmospheric concentration, residence time and global-warming potential. Kyoto gases include CO2, CH4, N2O and fluorinated gases; water vapour is not a Kyoto target. UPSC may test gas-source matching, feedbacks, weather versus climate, and mitigation versus adaptation.

Prelims revision checklist

Identify the definition first, then connect it to the relevant institution, date, process and example. Do not treat a scientific mechanism as a policy instrument, an international label as automatic domestic legal status, or a rank as ownership. Watch absolute words such as “always” and “only”; they are rarely correct unless part of a formal definition. In current-affairs questions, apply the stable principle and verify changing figures or variants from an official source.

Analogy

Greenhouse gases and global warming — Analogy

A greenhouse slows heat escape after sunlight enters; extra greenhouse gases are like adding too many blankets to an already warm planet.