Our recent results in Antarctica (Perera-Castro et al. 2020 Frontiers, 2021 JXB) highlights the effect of water availability not only on CO2 diffusion and photosynthetic capacity, but also on the temperatures experienced by a moss under sunlight due to the high specific heat capacity of water. How both photosynthesis and respiration respond to the interaction of temperature, radiation and water availability is crucial to predict the carbon balance of mosses in different scenarios of climate change. A first approach was done for Sphagnum species inhabiting the peatlands near Hyytiälä Forest Research Station (SMEAR II), Finland. Measurements of moss surface temperature under different hydric conditions was done during two weeks, covering different natural sun exposure. In addition, gas exchange at different temperatures and levels of moss hydration was measured for modeling carbon balance. Our results define the effects of different climate change scenarios on peatlands and establish the threshold for day and night temperature above which the existence of this ecosystem could be compromise.