This unit of mass represents one quadrillion grams (10¹⁵ g), which is exactly equal to one gigatonne. It is the standard unit used in global climate science and biogeochemistry to quantify the Earth's carbon cycle, atmospheric gas masses, and ice sheet melting rates. Using this unit avoids the confusion between US short tons and metric tonnes in international climate reports.
Heard on the job
Human activities add roughly ten petagrams of carbon to the atmosphere every year.
Insider tip
In climate literature, one petagram of carbon is mathematically identical to one gigatonne of carbon.