The forests of the Southwest Indian Ocean (SWIO) islands States are large carbon sinks. Rapid population growth in these islands is responsible for deforestation, which in turn is the main source of carbon dioxide (CO 2) emissions. This study is divided into two parts: The present study (Part 1) describes the seasonal vertical and surface spatial distribution of CO 2 over the SWIO islands and the temporal variation of surface CO 2 concentrations using data measured by the Tropospheric Emission Spectrometer (TES) on board the Aura Satellite. The CO 2 hotspots over these islands were identified and assessed to determine if they were associated with deforestation and forest degradation anthropogenic activities. Areas of minimum or low CO 2 atmospheric loading were also identified, and investigated to determine if they coincided with strong sink areas. Atmospheric CO 2 concentration was building-up from summer to spring. The spatial extent of CO 2 hotspots was found to increase from summer to spring. Over the study region, semi-permanent stable layers at 700 hPa and 500 hPa were shown to separate the troposphere into three layers of CO 2. Furthermore, surface CO 2 levels over all the study areas were found to be increasing during the period of the investigation. Part 2 of this study demonstrates the influence of meteorology and associated air transport on atmospheric CO 2 distribution over the study region.