Gigatonnen

Gigatonne, abbreviated Gt, is a unit of mass in the metric system representing one billion metric tonnes, equal to 10^12 kilograms. The term combines giga-, meaning a factor of 10^9, with tonne. In languages such as German and Dutch, the plural is Gigatonnen.

In climate science and policy, gigatonnes are used to express very large quantities, most notably greenhouse gas emissions measured as gigatonnes of CO2 equivalent per year (GtCO2e). The unit provides a convenient scale for comparing national or global emissions, energy use, and atmospheric burdens. Emissions are often reported in GtCO2e to combine different greenhouse gases into a common metric.

Conversions and scale: 1 Gt equals 1,000 megatonnes (Mt) and 10^12 kilograms. One gigatonne of CO2 is about 0.27 gigatonnes of carbon (GtC) because CO2 has a molecular weight of 44 and carbon has a weight of 12. Global fossil-fuel CO2 emissions are typically on the order of tens of GtCO2 per year.

Other uses include measuring the mass of large natural or industrial flows, such as mineral production or ecological burdens. In energy contexts, the term “gigatonne” is also used in the form of gigatons of TNT (Gt TNT) to denote energy, with 1 Gt TNT equaling about 4.184 exajoules (4.184 × 10^18 joules).