gigaton

Gigaton, short for gigatonne, is a unit of mass equal to one billion metric tonnes (10^9 t) or 10^12 kilograms. The symbol Gt is commonly used for mass, while GtCO2 denotes gigatonnes of carbon dioxide in emissions accounting.

In energy contexts, gigaton can refer to a unit of explosive energy, expressed as gigatonnes of TNT (Gt TNT). One gigatonne of TNT is defined as 4.184×10^18 joules (about 4.184 exajoules). This TNT‑equivalent scale is used to describe large energy releases or global energy magnitudes.

In climate science, emissions are frequently given in GtCO2 per year, representing gigatonnes of carbon dioxide. This unit facilitates comparisons of national or global emissions, such as annual totals that reach into the tens of gigatonnes of CO2.

Gigaton is also the title of Pearl Jam's eleventh studio album, released in 2020.

The word combines the SI prefix giga- (10^9) with ton(ne). In practice, usage varies by context: mass (Gt), energy scale (Gt TNT), and emissions (GtCO2) are distinct but related ways of expressing very large quantities.