Carbon Footprint Science

Measurement

CO2 equivalent converts all gases via Global Warming Potential (GWP): methane 28x CO2 over 100 years, nitrous oxide 265x. Emissions categorized into Scope 1 (direct), Scope 2 (purchased electricity), Scope 3 (all other indirect including supply chain). Scope 3 typically largest. Life Cycle Assessment tracks emissions from extraction through disposal.

Major Sources

Globally: energy production 25 percent, agriculture 22 percent, industry 21 percent, transport 16 percent, buildings 6 percent. For individuals in wealthy countries: vehicles (2-5 tonnes/year), home energy (1-4 tonnes), air travel (1-5+ per long-haul trip), diet (1.5-3 tonnes, red meat highest), and goods consumption.

National Variation

Per-capita varies 50x between highest and lowest countries, reflecting energy systems, transport, diet, consumption. Consumption-based accounting (including imports) increases wealthy nation footprints. Historical cumulative: US and Europe produced roughly half of all CO2 since 1850, relevant for equity in climate negotiations.

Limitations

Individual footprint focus criticized for deflecting from systemic change. Both individual action and systemic transformation needed, as consumer demand influences corporate behavior while infrastructure determines emission intensity. Quality carbon offsets can complement but not replace direct reductions.