The Arctic treeline, which encircles the north of the globe in an almost unbroken ring, is the frontline of climate change, where the trees – Scots pine, birch, larch, spruce, poplar and rowan – have been creeping towards the pole for 50 years already. The author has travelled through Scotland, northern Scandinavia, Siberia, Alaska, Canada and Greenland, witnessing the impact of climate change and the devastating legacies of colonialism and capitalism. But he also finds reasons for hope. Humans are creatures of the forest; we have evolved with trees. Rawlence asks where our co-evolution might take us next, underpinned by an urgent environmental message. ​In conversation with journalist, Nicola Cutcher.