This sociolinguistic study sets out to critically examine the way modals in prescribed English language teaching (ELT) textbooks in the English and French sub-systems of education in Cameroon convey conviction that potentially influences the attitudes of learners towards nature protection and degradation. More specifically, it looks into the opaque ways through which modals exude conviction in environment texts in Cameroonian ELT textbooks, and how this conviction affects communication regarding the protection of the natural world in diverse contexts. The work was corpus-based and was undertaken within the theoretical framework of Ecolinguistics propounded by Stibbe (2015). A mixed-methods approach was used in this research endeavour for the analysis of the collected data. The analysis reveals concerning trends. The results show that the modals deployed significantly exude low conviction in the environment texts, with the modal “can” dominating with 52.8%. Comparing newly prescribed and previously prescribed ELT textbooks in Cameroon, it clearly stands out that conviction levels remain stagnant, or decline, in the newer ELT textbooks. The findings hint that environment texts in ELT textbooks in Cameroon do not sufficiently achieve their purpose as recommended by the Competency-based Approach which anchors the country’s educational systems, and which requires connecting learners to their daily realities through classroom knowledge, and equipping them with contextual knowledge that aims at permitting them to resolve real-life situations. The prevalence of low conviction modals suggests that ELT textbooks in Cameroon may inadvertently hinder environmental conscientisation, thereby emphasising the need for linguistically informed textbook designers to promote effective environmental education.