Non-steady state desorption of dissolved carbon dioxide gas from green Nothofagus fusca heartwoood boards saturated with carbon dioxide gas at a pressure of 1.5 MPa was used to measure transverse dissolved carbon dioxide gas diffusivities at 1, 20 and 30 °C. Mean transverse diffusion coefficients were 0.6×10^-11m²s^-1 at 1 °C, 4.2×10^-11m²s^-1 at 20 °C, and 8.4×10^-11m²s^-1 at 30 °C. These are 0.6, 2.5 and 3.8% of the dissolved carbon dioxide gas diffusivities in water at 1, 20 and 30 °C respectively. The activation energy of dissolved carbon dioxide gas diffusion in green N. fusca heartwood is 59. 4 kJ mol^-1. This is three times the activation energy of dissolved carbon dioxide gas diffusion in water. This suggests the presence of a reaction mechanism between the dissolved carbon dioxide molecules and the cell wall constituents.