The current climate crisis necessitates effective mitigation action across all scales, including behaviours and lifestyle decisions at the individual level. Youth need to align lifestyle with the 2.1 tonnes of CO2 emissions per person per year required by 2050 to prevent the worse impacts of climate change (CC), yet little is known regarding their preparedness to act nor knowledge of the efficacy of the personal actions available to them. The main objectives of this study were to determine in a representative sample of 17–18 year old Canadians (n = 487) their: (1) beliefs around whether their activities or lifestyle choices can help to lessen CC, and (2) knowledge of the efficacy of individual-level behaviours in reducing greenhouse gas emissions (GGE). Results from the online survey (Likert scale) show that youth have limited confidence in how well their schooling has prepared them for CC and mitigation. However, the majority (88%) believe that their activities and lifestyle choices can help in mitigating CC. Knowledge of the relative efficacy of GGE-reducing actions was generally poor (Wilcoxon signed rank tests and open-ended responses) with, for instance, recycling overestimated and having one fewer child underestimated, suggesting that youth are not well equipped with the requisite knowledge to maximise CC mitigation through their personal choices. Our findings inform high school curricula and CC education and policy more broadly.