The study by Mercado et al. (2009) investigates the impact of changes in diffuse radiation on the global land carbon sink. The authors modified the JULES land surface scheme to account for the effects of variations in both direct and diffuse radiation on canopy photosynthesis. They found that variations in diffuse fraction, particularly during the "global dimming" period (1960-1999), enhanced the land carbon sink by approximately a quarter. However, under a climate mitigation scenario for the 21st century, where sulphate aerosols decline before atmospheric CO2 stabilizes, the "diffuse-radiation" fertilization effect declines rapidly to near zero by the end of the century. The study highlights the importance of diffuse radiation in enhancing plant productivity and the land carbon sink, and suggests that steeper cuts in fossil fuel emissions will be required to stabilize the climate if anthropogenic aerosols decline as expected.The study by Mercado et al. (2009) investigates the impact of changes in diffuse radiation on the global land carbon sink. The authors modified the JULES land surface scheme to account for the effects of variations in both direct and diffuse radiation on canopy photosynthesis. They found that variations in diffuse fraction, particularly during the "global dimming" period (1960-1999), enhanced the land carbon sink by approximately a quarter. However, under a climate mitigation scenario for the 21st century, where sulphate aerosols decline before atmospheric CO2 stabilizes, the "diffuse-radiation" fertilization effect declines rapidly to near zero by the end of the century. The study highlights the importance of diffuse radiation in enhancing plant productivity and the land carbon sink, and suggests that steeper cuts in fossil fuel emissions will be required to stabilize the climate if anthropogenic aerosols decline as expected.