© 2019 The Authors Achieving a global forest transition, that is, a shift from net deforestation to reforestation, is essential for climate change mitigation. However, both land-based climate change mitigation policy and research on forest transitions neglect key processes that relieve pressure from forests, but cause emissions elsewhere (‘hidden emissions’). Here, we identify three major causes of hidden emissions of forest transitions, that is, emissions from agricultural intensification, from woodfuel substitution, and from land displacement. Taken together, these emissions may compromise the climate change mitigation effect of national forest transitions. We propose to link analyses of hidden emissions of forest transitions with quantifications of full socio-ecological greenhouse-gas accounts and analyses of their politics. Such an integration allows for drawing lessons for effective and just climate change mitigation policies.