The paper discusses the carbon balance of tropical, temperate, and boreal forests, emphasizing the climatic influences on carbon dynamics. It reviews historical changes in the carbon balance of each biome and the evidence for a carbon sink in each forest type. The authors present a synthesis of micrometeorological, ecophysiological, and forestry data from three case-study sites to compare carbon cycling in these forest biomes. They highlight significant advances in understanding forest carbon balance but also point out critical uncertainties, particularly in soil carbon stocks. The paper also examines the historical and current state of forests, including the impact of human activities such as deforestation, logging, and land-use changes. It analyzes the carbon cycle of intact forests and the influence of climate variables like light availability, temperature, and soil moisture on carbon dynamics. The seasonal cycles of carbon uptake and loss at the three sites are illustrated, showing varying patterns influenced by their distinct climatic conditions. Overall, the study provides insights into the complex interactions between forest ecosystems and the global carbon cycle.The paper discusses the carbon balance of tropical, temperate, and boreal forests, emphasizing the climatic influences on carbon dynamics. It reviews historical changes in the carbon balance of each biome and the evidence for a carbon sink in each forest type. The authors present a synthesis of micrometeorological, ecophysiological, and forestry data from three case-study sites to compare carbon cycling in these forest biomes. They highlight significant advances in understanding forest carbon balance but also point out critical uncertainties, particularly in soil carbon stocks. The paper also examines the historical and current state of forests, including the impact of human activities such as deforestation, logging, and land-use changes. It analyzes the carbon cycle of intact forests and the influence of climate variables like light availability, temperature, and soil moisture on carbon dynamics. The seasonal cycles of carbon uptake and loss at the three sites are illustrated, showing varying patterns influenced by their distinct climatic conditions. Overall, the study provides insights into the complex interactions between forest ecosystems and the global carbon cycle.