Climate Change, GHG Accounting & Carbon Footprints

Engineering for a changing climate. Learn the greenhouse effect and radiative forcing, the main greenhouse gases and global warming potentials, carbon budgets and net zero, GHG accounting (GHG Protocol scopes 1–3, emission factors), carbon footprints of products and organisations, mitigation options (efficiency, renewables, electrification, CCS, nature-based), adaptation, and carbon markets — with Python calculating a factory's footprint.

Human emissions of carbon dioxide, methane and nitrous oxide have raised global temperature by about 1.1–1.2 °C since pre-industrial times. Limiting warming to 1.5–2 °C requires reaching net-zero CO₂ around mid-century, which touches every engineering discipline.

Engineers quantify emissions (you can't manage what you don't measure), design low-carbon alternatives, and adapt infrastructure to heatwaves, floods and sea-level rise.

An analogy

The atmosphere is like a bathtub with the tap (emissions) running faster than the drain (natural sinks): the water level (CO₂ concentration) keeps rising until the tap is turned down to match the drain — that's net zero.

The greenhouse effect

Sunlight warms the surface; the Earth radiates infrared; greenhouse gases (H₂O, CO₂, CH₄, N₂O, F-gases) absorb and re-emit it, keeping the planet ~33 °C warmer than without them. Adding more gases increases radiative forcing and warming. CO₂ has risen from 280 ppm (pre-industrial) to over 420 ppm.

GHG accounting

GHG Protocol scopes:

Mitigation hierarchy

Avoid (reduce demand), reduce (energy efficiency, process change), substitute (renewables, electrification, low-carbon materials), capture (CCS/CCUS), and offset only residual emissions with high-quality removals. Marginal abatement cost curves rank options by cost per tonne.

Net zero, markets and adaptation

Science-based targets align corporate reductions with 1.5 °C pathways. Carbon pricing (taxes, cap-and-trade like EU ETS, India's Carbon Credit Trading Scheme) internalises costs. Adaptation engineering redesigns drainage for heavier rainfall, cooling for heatwaves and coasts for sea-level rise, using climate projections and risk assessment.

Formulas

Worked example: Methane CO₂e

Given: Landfill emits 100 t CH₄/yr (GWP 27)

Find: CO₂e.

Answer: 2700 t CO₂e — capturing it for energy is high-value

Worked example: Commute footprint

Given: Car 20 km/day, 0.17 kg CO₂/km, 250 days

Find: Annual emissions.

Answer: 850 kg CO₂

Worked example: Forcing

Given: C = 420 ppm

Find: ΔF vs 280 ppm.

Answer: 2.17 W/m²

Scope 1 & 2 footprint and a solar mitigation

# Carbon footprint of a small factory (scope 1 and 2), GWP-100 (AR6)
diesel_L = 20000;        ef_diesel = 2.68      # kg CO2 per litre
gas_m3 = 50000;          ef_gas = 1.9          # kg CO2 per m3 natural gas
elec_kWh = 1.2e6;        ef_grid = 0.71        # kg CO2 per kWh (India grid approx.)
refrigerant_kg = 5;      gwp_r410a = 2256
scope1 = diesel_L * ef_diesel + gas_m3 * ef_gas + refrigerant_kg * gwp_r410a
scope2 = elec_kWh * ef_grid
total = (scope1 + scope2) / 1000
print(f"scope 1 = {scope1/1000:.0f} t CO2e, scope 2 = {scope2/1000:.0f} t CO2e, total {total:.0f} t CO2e")
# Effect of a 400 kWp rooftop PV (1500 kWh/kWp/yr)
pv = 400 * 1500
print(f"rooftop PV avoids {pv*ef_grid/1000:.0f} t CO2e/yr ({pv*ef_grid/1000/total*100:.0f}% of total)")
# scope 1 = 160 t CO2e, scope 2 = 852 t CO2e, total 1012 t CO2e
# rooftop PV avoids 426 t CO2e/yr (42% of total)

Purchased electricity dominates this factory's footprint because the grid is coal-heavy — so on-site solar is the single biggest lever. A small refrigerant leak (5 kg) is worth 11 tonnes of CO₂: high-GWP gases matter. Emission factors vary by country and year; use official sources (CEA, IPCC, DEFRA).

Common mistakes

Applications

Key takeaways

Going further