NDC Ratchet Wheel: 2D Pledge-Cycle Diagnostics

Global Stocktake Levers

Stocktake pressure 50%

Implementation gap 20%

BAU emissions growth 1.0%/yr

Pledge Cycle

Cycle 2025 · NDC round 1

Global emissions

40.0 Gt/yr

Mean ambition

18%

Cumulative CO₂

0 Gt

Projected warming

1.20°C

Ambition gap to 1.5°C pathway

— Gt/yr

How it works

This is the 2D companion to the 3D NDC Ratchet Mechanism Simulator — it runs the identical treaty equations, but renders them as a genuinely 2D-native ratchet wheel instead of a flattened camera view of the 3D bar field. Twelve spokes, one per negotiating bloc, each carry two independent readouts: a bright dot at radius = ambition (which the treaty's ratchet clause forbids from ever moving inward) and a translucent wedge whose length tracks that bloc's current emissions.

Ratchet:     a(t+1) = a(t) + pressure · (1 − a(t)) · 0.35   [monotonic, a ∈ [0,0.98]]
Implemented: cut(t)  = a(t) · (1 − gap)               [gap = pledge-vs-delivery shortfall]
Emissions:   E(t+1)  = E(t) · (1 + bau − cut(t)/5)     [compounded over 5 annual steps]
Cumulative:  C(t+1)  = C(t) + (E(t)+E(t+1))/2 · 5     [trapezoid over the 5-yr cycle]
Warming:     ΔT(C)   ≈ 1.20°C + 0.00045 °C/GtCO₂ · C  [TCRE, IPCC AR6 central estimate]

Ratchet wheel — because ambition dots can only move outward, the wheel's inner boundary traces the treaty's one-way ratchet directly; watch how the wedge lengths (emissions) don't always shrink even as the dots (ambition) rise, if BAU growth or the implementation gap eat the gains.
History strip — plots global emissions against the shrinking 1.5°C-consistent ceiling, cycle by cycle. Drag across it to scrub through past cycles: the ratchet wheel and stat readouts replay that cycle's snapshot while you hold the drag.
Warming gauge — a vertical thermometer reading the cumulative-emissions climate response, with the 1.5°C and 2.0°C treaty thresholds marked.
Stocktake pressure / Implementation gap / BAU growth — same three levers as the 3D version; drive the same equations.

Real-world relevance: this is the actual legal architecture behind the Paris Agreement — no external body sets national targets; ambition rises only through this repeated pledge/review/ratchet loop, which is why the "ambition gap" (pledged cuts vs. what a 1.5°C budget requires) is the single most-tracked number in international climate diplomacy.

12 negotiating blocs — ratchet wheel Drag the history strip to scrub cycles

Low ambition Mid ambition High ambition