There were perhaps fifty people in the audience and, as we drew to a close, a man in the front row who had until then sat mute rose to his feet and asked who would join him in setting up a Crickhowell group.

Tom somehow does this without the book feeling like a doom narrative - by weaving several congruent 'stories' together, of Wales past, present and future, including contemporary interviews with climate scientists and Wales' ancient history, against a backdrop of his journey through the landscape. It was the third night of an Extinction Rebellion (XR) action: a third night of almost no sleep, lying on the bare groundsheet of a pop-up tent, freezing cold and working our way respectively through nicotine gum (me) and cigarettes (Gerwyn).A minor road running along the east bank of the Afon Dulas near Esgairgeiliog, Powys might be Roman in origin.

Bullough is reluctant to firmly declare his position on this and the other big debates in Sarn Helen – including whether Wales should stop farming sheep. In the 12th century, the Normans reused part of the site and its earthworks to build the mediaeval church of St Mary's Church, Llanfair-ar-y-bryn.After all, on our current course, we will leave to our children a world whose average temperature will have increased by 3°C or more: a world of conflict and starvation, mass displacement and mass extinction. If I could travel back to those times – the times of The Claude Glass and Konstantin – and ask myself why I was writing, what I was writing in service of, I wonder how I would reply. Nevertheless, Bullough makes a persuasive case for it here, in and around his rich depictions of the homeland he loves so much.

Sarn Helen, his first work of non-fiction, was longlisted for the Wainwright Prize for writing on conservation. Fairbourne, on the south side of the Mawddach estuary not far from Saint Elen’s home, is the first village in Britain expected to be lost to climate change. From the author of Addlands, and featuring illustrations by Jackie Morris, an immersive and evocative non-fictional journey through Wales and a revelatory meditation on the nation’s past, present and future. What was new, for me, was that writing on this subject did not necessarily alienate people – that an honest piece of writing could actually engage, which is to say, in a small way, help – which meant that words matter, after all.His one digression from the Welsh road - a transcript of his defense when he was jailed in London after an Extinction Rebellion protest - is in particular deeply moving. The second stage of the Sarn Helen route is a brilliantly fun day on a bike, and one where you’ll be glad of your fat rubber and wide gearing as you pass through Britain’s first trail centre at Coed-y-Brenin.