Every additional tonne of carbon dioxide emissions adds to global warming1. This means that decisions to approve new fossil fuel projects represent pivotal moments in shaping Earth’s future climate trajectory. Yet, the specific additional global warming caused by project-level CO2 emissions, and the impacts of that warming, are rarely incorporated into decision-making on the acceptability of new fossil fuel projects. Here, we show how quantifying this additional warming enables concrete, foreseeable consequences to be identified and evaluated in a formal risk assessment framework. This approach reveals that major socioeconomic and environmental consequences can be attributed to CO2 emissions associated with individual fossil fuel projects, contrary to the pervasive unquantified claims of negligible risks by project proponents. Furthermore, as countries pursue rapid decarbonisation aligned to their Nationally Determined Contributions, the CO2 emissions from individual fossil fuel projects can, within decades, dominate and even exceed legislated national emission limits. The practical, future-focused approaches demonstrated here offer a critical bridge between climate science and decision-making, with immediate relevance to choices that will shape Earth’s climate for decades to centuries to come.
