The measurement of carbon dioxide (CO₂) concentration is crucial in fields such as climate change mitigation, process control, indoor air quality management, and medical diagnostics. Fiber-optic-based CO₂ sensors have garnered increasing attention due to their immunity to electromagnetic interference, miniaturization, and low power consumption. This paper reviews recent advancements in fiber-optic CO₂ sensing technologies, focusing on improvements in sensitivity, selectivity, stability, and response time through innovative materials and structural designs. These advancements expand their applications in climate monitoring, smart infrastructure, healthcare, and environmental safety, contributing to sustainable and efficient sensing solutions.