Discuss the significance of the carbon budget approach for climate justice. Why has it remained marginal in multilateral climate negotiations?

The carbon budget is the CO2 still allowed under a temperature limit: 500 GtCO2 from 2020 for a 50% chance of 1.5°C [1]. It asks who consumed this finite space, a question negotiations have avoided.

Significance for climate justice

• Makes responsibility measurable: about 2,400 GtCO2 was emitted during 1850–2019 [1]; the first Global Stocktake (GST) acknowledged that historical emissions already account for about four-fifths of the 1.5°C budget [2].
• Exposes inequity: India, with over 17% of world population, contributed about 4% of cumulative emissions during 1850–2019 [3], and so claims to have used far less than its fair share [4].
• Gives content to CBDR-RC: Paris Article 2.2 requires implementation reflecting equity [5]; a budget lets that be tested in numbers and supports later peaking for developing countries [5].
• Links mitigation to finance: India, which objected to the COP29 finance goal (NCQG), demands that developed countries' commitments reflect their contribution to cumulative emissions [6].

Why it remains marginal

• Bottom-up design: under Paris Article 4.2 each Party sets its own NDC [5]; even the GST calls for efforts "in a nationally determined manner" [2]. No national shares exist.
• Fear of liability: dividing the budget by history would convert past emissions into claims for finance and faster cuts. The GST states a global share but names no country [2].
• No agreed equity formula: per-capita, historical and capability-based shares give different results, and rising emitters also face scrutiny because the atmosphere counts every new tonne.
• Scientific uncertainty: non-CO2 assumptions alone move the 1.5°C estimate between 300 and 600 GtCO2 [1], which lets Parties contest any allocation.
• Temperature-path framing: with UNEP declaring no-or-limited overshoot of 1.5°C out of reach [7], talks now centre on overshoot, a single global curve that names no country.

The budget thus turns equity from principle into arithmetic, but treaty design and fear of liability keep it marginal. The next Global Stocktake should publish a budget figure beside national cumulative shares, with finance goals reflecting them. This would honour CBDR-RC and advance SDG 13, making climate action credible and just.