Greenhouse Gases (GHGs)

Greenhouse Gases (GHGs)

Key Notes

Greenhouse gases absorb and emit infrared radiation, helping retain heat in the Earth's climate system. The natural greenhouse effect makes Earth habitable, but increasing concentrations of greenhouse gases due to human activities strengthen this effect.

• Carbon dioxide (CO₂): Released by fossil fuel combustion, cement production, deforestation and land-use change.

• Methane (CH₄): Emitted from livestock, rice cultivation, landfills, fossil fuel production and wetlands.

• Nitrous oxide (N₂O): Associated with nitrogen fertilisers, agricultural soils, industrial processes and combustion.

• Water vapour: The most abundant natural greenhouse gas; its atmospheric concentration responds strongly to temperature.

• Ozone (O₃): Tropospheric ozone is a greenhouse gas and air pollutant; stratospheric ozone protects life from harmful ultraviolet radiation.

• Fluorinated gases: Include HFCs, PFCs, SF₆ and NF₃. Many have high global warming potentials.

• Global Warming Potential (GWP): Compares the warming effect of a greenhouse gas with that of CO₂ over a specified time horizon.

• Carbon dioxide equivalent (CO₂e): Expresses emissions of different greenhouse gases using a common warming-impact unit.

• Black carbon: A light-absorbing component of soot that warms the atmosphere and darkens snow and ice; it is not a greenhouse gas in the conventional sense.

• Montreal Protocol: Primarily addresses ozone-depleting substances; the Kigali Amendment phases down HFC production and consumption.

Key Pointers for UPSC

• CO₂ is a major driver of long-term human-caused warming because of its large emissions and long-lasting accumulation.

• Methane is more potent than CO₂ per unit mass over standard GWP comparison periods, but it generally remains in the atmosphere for a much shorter time.

• Water vapour is primarily a climate feedback rather than the principal initial driver of current human-caused warming.

• CFCs contribute to ozone depletion and are also powerful greenhouse gases.

• The ozone hole and global warming are different environmental problems, although some substances affect both.

• GWP values depend on the selected time horizon and scientific assessment.

MCQs

Q1. Which of the following is a major long-lived greenhouse gas emitted by human activities?

1. Carbon dioxide

2. Nitrogen

3. Argon

4. Helium

Correct answer: 1) Carbon dioxide.

Explanation: CO₂ is released in large quantities by fossil fuel use and land-use change and contributes substantially to long-term global warming.

Q2. Which greenhouse gas is closely associated with rice cultivation, livestock and landfill emissions?

1. Oxygen

2. Methane

3. Argon

4. Neon

Correct answer: 2) Methane.

Explanation: Methane is produced by anaerobic decomposition in wetlands, rice fields and landfills and through enteric fermentation in ruminants.

Q3. The Kigali Amendment to the Montreal Protocol primarily addresses:

1. Carbon monoxide emissions

2. HFCs

3. Sulphur dioxide emissions

4. Plastic waste

Correct answer: 2) HFCs.

Explanation: Hydrofluorocarbons were introduced as alternatives to many ozone-depleting substances, but they can have high global warming potentials. The Kigali Amendment provides for their phasedown.