This study attempts to quantify the radiative impact over Reunion Island (21°S, 55°E) in the southern tropical Indian Ocean of the aerosols and water vapor injected in the stratosphere by the eruption on 15 January 2022 in the South Pacific of the Hunga Tonga-Hunga Ha’apai underwater volcano. Ground-based lidar and satellite passive instruments are used to parametrize a state-of-the-art radiative transfer model for the first thirteen months after the volcano eruption. The descending rate of the aerosol volcanic plume is -0.008 km day-1. At this rate, aerosols are expected to be present in the stratosphere until the first half of 2025. The overall aerosol and water vapor impact on the Earth’s radiation budget for the whole period is positive (warming, +0.06 ± 0.45 W m-2) and dominated by the aerosol impact. However, the decreasing rate with time of the aerosol warming effect is larger than that of the water vapor cooling effect, so that, in the long run, the impact on the Earth’s radiation budget might reduce to quasi-neutral, or even become slightly negative. At the Earth’s surface, aerosols are the main driver and produce a negative (cooling, -0.91 ± 0.61 W m-2) radiative impact with also a decreasing tendency with time. Heating/cooling rate profiles show a clear vertical difference in the stratosphere between the aerosol warming impact (17 to 25 km) and the water vapor cooling one (25 to 40 km).