GtCO2e

GtCO2e stands for gigatonnes of CO2 equivalent and is a metric used to express greenhouse gas emissions in a single common unit. It converts the various greenhouse gases into an equivalent amount of CO2 that would produce the same radiative forcing over a specified time horizon, typically 100 years. This allows direct comparison across gases with different lifetimes and strengths.

Calculation relies on Global Warming Potential (GWP) values, published by bodies such as the IPCC. For a given gas, CO2e equals the mass emitted multiplied by its GWP, and the total CO2e is the sum of contributions from all considered gases (for example CO2, CH4, N2O, and fluorinated gases). Global emissions inventories are often reported in GtCO2e per year, enabling comparisons by sector (energy, transport, industry, agriculture) and tracking progress toward climate targets.

Limitations include dependence on the chosen GWP values and time horizon, which can influence comparative outcomes. The metric also simplifies differences in gas lifetimes and atmospheric behaviors, and may not capture all climate effects such as certain aerosols, regional feedbacks, or land-use changes. Despite these caveats, GtCO2e remains a widely used tool for policy analysis, corporate reporting, and climate modeling.

Typical values illustrate the scale: CO2 has a GWP of 1 by definition; methane (CH4) has a 100-year GWP around 28; nitrous oxide (N2O) about 265; fluorinated gases vary broadly from hundreds to tens of thousands (e.g., SF6 is ~23,500). These relationships underpin how diverse emissions are consolidated into a single CO2e figure for reporting and budgeting.