Ben Rawlence is a British writer based in the Black Mountains of Wales where he is the founding director of Black Mountains College, an institution devoted to creative and adaptive thinking in the face of the climate and ecological emergency. His latest book The Treeline: the last forest and the future of life on earth explores the shifting frontier of the boreal forest and the mysterious workings of the forest upon which we rely for the air we breathe. In this episode of Nature Revisited, Ben talks about the boreal forest - which contains about one third of the the earth's trees - and the myriad repercussions its northern expansion is having on a local and global scale.