CO2's dominance by volume and weight
While carbon dioxide makes up the bulk of anthropogenic greenhouse gas emissions by mass, it tells only half the story. A molecule of methane traps roughly 80-120 times more heat than CO2 over a 20-year window, yet atmospheric concentrations of methane are far smaller. Nitrous oxide is equally potent gram-for-gram, retaining warmth for over a century. This discrepancy between abundance and warming potential is why policy-makers track both absolute emissions and CO2-equivalent (CO2e) measures.
The chart typically separates gross tonnage from radiative forcing (the actual warming energy per molecule). Without this distinction, reducing methane from livestock farming can look less urgent than it truly is for near-term climate goals.
Global warming potentials and time horizons
Climate impact scales with the timeframe you choose. Methane is a short-lived gas, degrading in the atmosphere within 12 years, so its 20-year GWP of ~84 reflects intense but temporary warming. Over 100 years, its impact shrinks to ~28 relative to CO2. Nitrous oxide, by contrast, persists for over a century, so its long-term GWP remains consistently high. This time-horizon sensitivity drives competing climate strategies: short-term policies prioritize methane cuts, while long-term decarbonization targets emphasize CO2.
Converting all gases to CO2-equivalent using a consistent time horizon ensures apples-to-apples comparison across emissions inventories and climate commitments.