Climate anxiety has emerged as a significant mental health concern among young people worldwide, yet research on its prevalence and impacts remains limited. This cross-cultural study examines climate anxiety levels among 3,847 students aged 15-19 across 28 countries, using validated psychological assessments and novel climate concern scales. We found that 76% of participants experienced moderate to high climate anxiety, with strongest correlations in coastal regions (r=0.78, p<0.001). Female students reported 1.4x higher anxiety levels than males, while students from developing nations showed greater resilience despite higher vulnerability. The research identifies effective coping mechanisms and provides recommendations for educational institutions to support student mental health in the climate era.