2.3.12 (HL)—Lithosphere carbon stores

Fossil fuels and limestone hold carbon for geological times because burial and rock cycling isolate it from rapid biological exchange.

Organic carbon is stored in coal, oil and gas; inorganic carbon is stored in carbonate rock. Their long residence time makes their natural release slow compared with combustion or mining.

A limestone deposit can retain carbon for millions of years, but heating it for cement production transfers part to CO₂ much faster.

Carbonate rock and geological isolation slow exchange; the store is not rapidly available to organisms.

Long residence time does not mean the store is irrelevant; extraction can change its flux abruptly.