Employing Stibbe's (2021) framework for Eco linguistic discourse analysis, the present study investigates conviction in three speeches delivered by Greta Thunberg, the 19-year old eco-activist. These are: the 2019 UN Climate Action Summit, the 2020 World Economic Forum, and the 2021 26^th UN Conference of the Parties (COP 26). The aims of the study are threefold: (1) examine the linguistic devices used to construct the conviction that the people in power are not taking action to counter climate change; (2) investigate the functions of these linguistic devices; (3) identify the discourse type of the speeches, i.e. whether they are destructive, ambivalent or beneficial. Results show that a number of linguistic devices are used to construct conviction such as quantifiers, modality, metaphors and repetition. The functions of the linguistic devices used include criticizing the people in power for not taking action to stop climate change, holding them responsible for the ill consequences of the rise in global temperature, and asserting that they only pay lip service regarding finding a solution for the problem of climate change. Results also show that Greta Thunberg's speeches enhance beneficial discourse as they serve to urge world leaders to take a climate action.