Purpose <p>The current linear approach to manage waste plastics is straining already limited fossil fuel resources. Pyrolysis offers a promising alternative, converting plastic waste into fuels while helping to reduce greenhouse gas (GHG) emissions and supporting a circular plastics economy. This study aims to evaluate the GHG emission impacts of plastic-to-fuel pyrolysis and develop a modeling approach to forecast GHG emissions under different process conditions.</p> Methods <p>This study presents an agile modeling framework that predicts GHG emissions based on variations in feedstock and process conditions. To address variability in pyrolysis systems, a kinetic model was integrated into the framework, allowing for the quantification of GHG emissions across different feedstock compositions, operating temperatures, vapor residence times, energy sources, co-product handling strategies, and conversion efficiencies.</p> Results <p>The model identified operating conditions where the plastic-to-fuel pyrolysis of mixed plastic waste composed of high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP) minimized GHG emissions associated with the production of 1 MJ of produced fuel. Reducing reactor temperature from 600 to 550 °C reduced GHG emissions from 15.9 gCO₂ eq./MJ of fuel at 600 °C, VRT 2 to 15.4 gCO₂ eq./MJ of fuel at 550 °C, VRT 2, while increasing the VRT from 2s to 6s further reduced emissions to 14.8 gCO₂ eq./MJ of fuel. These reductions were primarily attributed to higher liquid fuel yields under the operating conditions. Furthermore, variations in feedstock composition from PP-rich to HDPE-rich mixtures increased the GHG emissions by an average value of 5.3 g CO₂ eq./MJ. Additionally, increasing fuel gas-to-electricity conversion efficiency was found to reduce GHG emissions by up to 41%, particularly under configurations involving surplus electricity export. Results further demonstrated strong regional dependency, where carbon-intensive electricity grids increased the benefits associated with electricity co-generation and displacement credits.</p> Conclusions <p>This modeling platform provides an approach for examining GHG emissions under dynamic processing conditions in plastic pyrolysis and assessing the impacts of plastic-stream composition. Variability in waste plastic feedstocks strongly influences GHG emissions. Feedstocks that require less pyrolysis energy or generate higher liquid-oil yields result in proportionally lower overall GHG emissions. System-level GHG emissions are further shaped by the regional energy supply mix and the efficiency of fuel-gas–to-electricity conversion. Advancing the dynamic simulation in plastics recycling will provide insights for guiding process improvements and policy choices toward effective waste management strategies.</p>