The Paris Agreement set ambitious goals: limit global warming to well below 2°C above pre-industrial levels, and pursue efforts to limit warming to 1.5°C. That half-degree difference might seem negligible—barely noticeable on a household thermometer. Yet climate scientists emphasize that every fraction of a degree matters, with 1.5°C representing a meaningful threshold with significant implications for ecosystems, societies, and the viability of some nations. Understanding why 1.5°C became the target—and why we're likely to miss it—is essential for grasping where climate policy stands.