The study investigates the impact of changes in diffuse radiation on the global land carbon sink. It uses a global model modified to account for the effects of variations in both direct and diffuse radiation on canopy photosynthesis. The results show that variations in diffuse fraction, associated with the "global dimming" period (1960-1999), enhanced the land carbon sink by approximately a quarter. Under a climate mitigation scenario for the 21st century, where sulphate aerosols decline before atmospheric CO₂ is stabilized, this "diffuse-radiation fertilisation" effect declines rapidly to near zero by the end of the 21st century. Solar radiation reaching the Earth's surface is the primary driver of plant photosynthesis. Leaf photosynthesis increases non-linearly with incident PAR, saturating at light levels often exceeded on bright days. In clear-sky conditions, a fraction of the canopy is illuminated by direct solar radiation, while the rest is in the shade. In contrast, under cloudy or sulphate-aerosol-laden skies, sunlight is more scattered, leading to more uniform irradiance and increased light-use efficiency. The net effect on photosynthesis depends on the balance between reduced total PAR and increased diffuse fraction. The study used the JULES land surface scheme to simulate the impact of diffuse radiation on canopy photosynthesis. It found that the modified JULES model could reproduce different light response curves under diffuse and direct radiation. The study performed multiple global simulations from 1901 to 2100, showing that changes in diffuse radiation significantly affect the land carbon sink. The results suggest that increases in diffuse fraction have enhanced the global land carbon sink by 23.7% from 1960 to 1999. The study also examined the impact of the Mount Pinatubo eruption on the land carbon cycle, finding that the anomalous land sink was partly due to enhanced canopy photosynthesis from increased diffuse fraction. The study concludes that anthropogenic aerosols have enhanced land carbon uptake despite significant reductions in total PAR. Future projections under an environmentally friendly emissions scenario suggest that diffuse-radiation fertilization will decline, requiring steeper cuts in fossil fuel emissions to stabilize the climate.The study investigates the impact of changes in diffuse radiation on the global land carbon sink. It uses a global model modified to account for the effects of variations in both direct and diffuse radiation on canopy photosynthesis. The results show that variations in diffuse fraction, associated with the "global dimming" period (1960-1999), enhanced the land carbon sink by approximately a quarter. Under a climate mitigation scenario for the 21st century, where sulphate aerosols decline before atmospheric CO₂ is stabilized, this "diffuse-radiation fertilisation" effect declines rapidly to near zero by the end of the 21st century. Solar radiation reaching the Earth's surface is the primary driver of plant photosynthesis. Leaf photosynthesis increases non-linearly with incident PAR, saturating at light levels often exceeded on bright days. In clear-sky conditions, a fraction of the canopy is illuminated by direct solar radiation, while the rest is in the shade. In contrast, under cloudy or sulphate-aerosol-laden skies, sunlight is more scattered, leading to more uniform irradiance and increased light-use efficiency. The net effect on photosynthesis depends on the balance between reduced total PAR and increased diffuse fraction. The study used the JULES land surface scheme to simulate the impact of diffuse radiation on canopy photosynthesis. It found that the modified JULES model could reproduce different light response curves under diffuse and direct radiation. The study performed multiple global simulations from 1901 to 2100, showing that changes in diffuse radiation significantly affect the land carbon sink. The results suggest that increases in diffuse fraction have enhanced the global land carbon sink by 23.7% from 1960 to 1999. The study also examined the impact of the Mount Pinatubo eruption on the land carbon cycle, finding that the anomalous land sink was partly due to enhanced canopy photosynthesis from increased diffuse fraction. The study concludes that anthropogenic aerosols have enhanced land carbon uptake despite significant reductions in total PAR. Future projections under an environmentally friendly emissions scenario suggest that diffuse-radiation fertilization will decline, requiring steeper cuts in fossil fuel emissions to stabilize the climate.