Stratocumulus (Sc) is the most common cloud type on Earth, covering approximately 20–25 % of the planet's surface at any given time. It consists of grey or whitish patches, sheets, or layers with rounded masses (rolls or cells), arranged in fairly regular patterns. It occupies the low étage (600–2,000 m) and is composed of water droplets, occasionally mixed with ice crystals at its top.
Stratocumulus typically forms in stable or weakly unstable environments where a temperature inversion caps vertical growth. The characteristic cellular or roll pattern results from shallow convection beneath the inversion — air rises in the cloud centres and sinks in the gaps, creating the patchwork appearance. The individual elements (cloudlets) are larger than those in altocumulus — typically spanning more than 5° when observed at 30° elevation above the horizon.
For climate, marine stratocumulus is enormously important: vast decks of this cloud persist over cool ocean currents off the west coasts of continents (California, Peru, Namibia, Canary Islands), reflecting sunlight and cooling the Earth by several degrees. Any change in stratocumulus coverage due to global warming could amplify or moderate climate change — making it one of the biggest uncertainties in climate models. On land, stratocumulus produces at most light drizzle and is associated with grey, overcast but dry conditions — the typical winter sky of northern Europe.