Dicranum undulatum is categorised as ‘Endangered’ on the Red Data List for Wales, and is considered to be of principal importance for conservation under Section 7 of The Environment (Wales) Act 2016. Due to the widespread loss and degradation of peatlands, it has undergone a large decline in Britain, and the only surviving population in Wales occurs in Denbighshire, on Whixall and Bettisfield Mosses. The species was known from Cors Fochno, where it was last seen in 1967. Reasons for the extinction are uncertain, but former fires may be partly to blame. Following significant efforts to improve the habitat condition of the bog, including the elimination of fires and large-scale hydrological restoration, a recent assessment concluded that parts of the site appear to contain favourable habitat for D. undulatum and that reintroduction may be a possibility. The aim of this study is to investigate whether a suitable macroclimate for the species is likely to occur at Cors Fochno in the medium-term.