AbstractBiogenic volatile organic compound (BVOC) emissions from subarctic ecosystems have shown to increase drastically in response to a long‐term temperature increase of only 2°C. We assessed whether this increase takes place already after 3 years of warming and how the increase changes over time. To test this, we measured BVOC emissions and CO2 fluxes in a field experiment on a subarctic wet heath, where ecosystem plots were subjected to passive warming by open top chambers for 3 (OTC3) or 13 years (OTC13) or were kept as unmanipulated controls. Already after 3 years of moderate temperature increase of 1–2°C, warming increased the emissions of isoprene (five‐ to sixfold) and monoterpenes (three‐ to fourfold) from the subarctic heath. The several‐fold higher BVOC emissions in the warmed plots are likely a result of increased vegetation biomass and altered vegetation composition as a shift in the species coverage was observed already after 3 years of warming. Warming also increased gross ecosystem production and ecosystem respiration, but the increases were much lower than those for BVOCs. Our results demonstrate that the strong BVOC responses to warming already appeared after 3 years, and the BVOC and CO2 fluxes had acclimated to this warming after 3 years, showing no differences with another 10 years of warming. This finding has important implications for predicting CO2 and BVOC fluxes in subarctic ecosystems.