Butterflies are among the most studied insect groups in the world, partly because they are easy to see and partly because they react quickly to changes in their surroundings. This makes them very useful as indicators of environmental health. Over the last few decades, climate change has started to leave clear marks on butterfly populations across continents, with shifts in their range, timing of flight, and overall diversity becoming visible in field records. This study looks at how rising temperatures, changing rainfall patterns, and habitat shifts are affecting butterfly diversity, with a particular focus on data from tropical and sub-tropical regions, including India. A combination of field surveys and secondary data from long-term monitoring stations was used to track changes in species richness, evenness, and abundance across selected sites between 2018 and 2024. Standard biodiversity indices such as the Shannon-Wiener index and Simpson's index were calculated and compared across years. The results show that several heat-sensitive species have declined sharply, while a few generalist species have expanded their range into higher elevations and cooler pockets. Flight periods of many species have shifted earlier by about 8 to 14 days compared to a decade ago. The overall species richness in the study sites dropped by nearly 17%, with the worst impact seen in forest-edge habitats. The study concludes that climate change is reshaping butterfly communities in subtle but serious ways, and urgent conservation steps are needed.