Interest and effort in re-introducing civil supersonic transport (SST) airplanes as a means of travel have surged in the past decade. Current major endeavours are underway for both commercial and business supersonic vehicles. The value proposition for these aircraft exists for high-networth individuals and business-class travellers who value time savings more than the potential cost associated with supersonic travel. Although these new SSTs in development will be more fuel-efficient than the SSTs of the past, they will have higher relative fuel burn (FB) than current subsonic aircraft flying the same routes. Burning more fuel while having less passengers (pax) on board per trip yields significantly higher FB per passenger for these operations. However, the relatively small market capturable by supersonic commercial operations means that in the broader scope of global aviation, the effect of increased FB per pax on fleet-level carbon dioxide (CO2) emissions is unknown. In addition, due to uncertainties in the effectiveness of sonic boom reduction technologies,it remains unclear whether supersonic over-land flight will be permitted in the future. Part I of this twopart study aims to formulate a methodology that employs a bottom-up approach for estimating the demand of supersonic commercial operations in coming decades, using only publicly available subsonic baseline-fleet data. The constraints and limitations identified while using publicly available data is key to understanding the data requirements for executing market assessment studies of this type. Part II of two-part study will fill many of the gaps identified in this public-data-only Part I, in order to refine the study process and results. After proposing the bottom-up methodology for estimating demand, the procedure is implemented and the environmental impact of the estimated market is determined. The results identify a supersonic commercial flight demand of 47 to 786 daily, global flights in 2035, growing to 71 to 1,180 daily, global flights in 2050, corresponding to low and high demand scenarios, respectively. These fleets will contribute an approximate 1.96 to 28.61 megatonnes (MT) of CO2 to global aviation emissions in 2035, growing to 3.01 to 43.08 MT of CO2 in 2050. These emissions in 2035 and 2050 represent a 0.21 to 3.12% and 0.33 to 4.69% increase in CO2 emissions with respect to the 2018global subsonic commercial aviation fleet.