A changing planet has underscored the need for a new paradigm for guiding human activity. To that end, scientists have introduced the planetary boundaries framework which outlines a safe operating space for humanity. They identify nine biophysical processes that are integral to the stability of the Earth system. Central to the framework is the concept of the precautionary principle. Each planetary boundary is associated with a threshold past which nonlinear feedbacks are likely to occur to that process. The purpose of this research is to estimate an upper bound for the rate of CDR while staying within those biophysical limits. Constraints that define three planetary boundaries—blue water, green water, and land-system change—as well as a limit on overall energy use are used to maximise the negative emissions from a portfolio of technologies. The overall goal of this study is to provide an alternative framework for modelling carbon dioxide removal that produces portfolios of NETs that are distinctively different from those of IAMs.