Science-Based Target Pathway: Carbon Budget Phase Diagram (2D)

Companies setting a net-zero target under the Science Based Targets initiative (SBTi) commit to a linear annual reduction rate against a baseline emissions inventory — 4.2% a year for a 1.5°C-aligned pathway, or 2.5% a year for a well-below-2°C pathway — with at least 90% absolute reduction required by 2050 and only the residual 10% neutralized through carbon removal. This 2D version traces E(t) = E0·(1-r)^t directly as a function graph rather than rendering it as a field of bar towers: an upper panel plots actual vs. required emissions with a shaded excess/deficit area and the net-zero residual ceiling, while a lower panel is an independent cumulative-budget phase diagram — allowed budget on one axis, used budget on the other — where the diagonal marks an exactly-on-pathway company and any drift above it marks a company that has already overspent its own science-based carbon budget.