1. The Arctic world

‘The Arctic world’ begins with the definition of the Arctic, which is understood as the land, sea, and ice lying north of the Arctic Circle set at a latitude of approximately 66.5° N. The Arctic tree line is a robust indicator of Arctic-ness as everything to the north is a landscape characterized by shrubs, dwarf trees, and lichen. Arctic warming occurs at least twice as rapidly as the global average, which is a phenomenon known as Arctic amplification. Since 1980, the warming trajectory in the Arctic has been much steeper than that of the rest of the planet.