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Global & Regional Environmental Issues
Greenhouse Effect & Global Warming Potential
Greenhouse gases, radiative forcing, GWP and CO₂-equivalent accounting of emissions.
PART 1
Topic Breakdown & Traps
The Engineering Principle
Greenhouse gases (GHGs) are largely transparent to incoming short-wave solar radiation but absorb outgoing long-wave (infrared) radiation, warming the surface — the greenhouse effect. Each gas's warming impact relative to CO₂ over a time horizon is its Global Warming Potential (GWP). Emissions are aggregated as CO₂-equivalent by multiplying each gas's mass by its GWP.
The Core Formula Matrix
CO₂-equivalent:
Approx. 100-yr GWPs: CO₂ = 1, CH₄ ≈ 28, N₂O ≈ 265, many HFCs ≫ 1000.
Mechanism: GHGs absorb terrestrial IR, re-emitting toward the surface.
Key GHGs: CO₂, CH₄, N₂O, water vapour, halocarbons.
Approx. 100-yr GWPs: CO₂ = 1, CH₄ ≈ 28, N₂O ≈ 265, many HFCs ≫ 1000.
Mechanism: GHGs absorb terrestrial IR, re-emitting toward the surface.
Key GHGs: CO₂, CH₄, N₂O, water vapour, halocarbons.
The ‘IIT Traps’
- ⚠GHGs absorb long-wave IR, not incoming visible/UV solar radiation.
- ⚠GWP is relative to CO₂ (= 1) over a stated horizon (usually 100 yr).
- ⚠Methane has a high GWP (~28) despite a shorter atmospheric lifetime.
📚 Standard references
- IPCC Assessment Reports — Intergovernmental Panel on Climate Change
- Environmental Studies — Erach Bharucha · Global Environmental Issues
PART 2
Progressive 3-Tier Question Suite
Q1MEDIUM2 Marks · NAT
Emissions consist of 50 t CO₂, 4 t CH₄ (GWP 28) and 1 t N₂O (GWP 265). The total carbon footprint is _____ t CO₂-e.
Q2BASIC1 Mark · MCQ
The greenhouse effect arises because GHGs are largely transparent to incoming solar radiation but absorb outgoing:
Q3HARD1 Mark · MCQ
The Global Warming Potential (GWP) of a greenhouse gas is defined relative to: