‘Trees no longer offer comfort, but warning,’ writes Ben Rawlence in the prologue of The Treeline. ‘These days I cannot look at the mountain, the forest or the field without feeling the ground tremble in both anticipation and memory.’ This is an author who is determined to let us know how much he feels and cares about his subject – which is, in a nutshell, the Arctic treeline, the northern edge of the great boreal forest, and its encroachment on the Arctic tundra. ‘The trees are on the move. They shouldn’t be,’ he writes. This northerly spread of the forest, he and many scientists believe, is a potential threat to ‘the future of life on Earth’. It certainly threatens a large-scale loss of Arctic tundra, terrain that is, among other things, a major carbon ‘sink’.

Rawlence is not himself a scientist – his previous books have been about a refugee camp in the Horn of Africa and the war in Congo – but, when it comes to environmental science, he knows his stuff. In The Treeline, he explores the subject by focusing on six tree species that form a large part of the boreal forest: