Reaching net-zero within the next two decades requires an urgent shift from petroleum-based to sustainably-sourced fuels and chemicals. Despite substantial investments and government support since the 1990s, the pace of this transition remains slow. Numerous technologies designed for these efforts, including corn ethanol, algal biodiesel, and crop-derived plastics, fell short, failing to deliver on environmental benefits or causing unintended side effects. Such outcomes indicate that emerging decarbonization technologies are not inherently sustainable. Life Cycle Assessment (LCA) can be a pivotal tool for evaluating the impacts of nascent technologies from very early development stages, ensuring that such pitfalls are avoided. LCA can guide technology development and scaling by identifying critical improvement areas, and support informed decision-making and policy development for decarbonization. Yet, the lack of quality data and robust assessment methodologies, often results in misleading and inconsistent LCA findings. In this talk, I will discuss two case studies addressing these limitations by introducing systematic LCA methodologies supported by field measurements. The first study concerns an advanced marine biofuel. Combustion emissions measured aboard a bulk carrier vessel were combined with data from a biofuel production plant to perform a representative LCA that underscores the biofuel's life cycle decarbonization benefits compared to fossil-based diesel. The second study compares “end-of-pipe” sulfur emission abatement marine technologies with “start-of-pipe” low sulfur marine fuels in a comprehensive manner, encompassing a full spectrum of emissions data. Contrary to popular belief, it is shown that 'start-of-pipe' options may not always be the cleaner choice. These studies advocate for holistic LCA methodologies for realistic, transparent, and informative technology assessments.