Carbon budget as contested commons

Sources

Wikipedia: Carbon budget (fetched 2026-08-14)
Our World in Data: CO₂ emissions (Hannah Ritchie, Max Roser, fetched 2026-08-14)
Global Carbon Project: https://www.globalcarbonproject.org/carbonbudget/

The IPCC defines carbon budget as "maximum amount of cumulative net global anthropogenic CO₂ emissions that would result in limiting global warming to a given level" (IPCC AR6 WG1).
As of January 2023, ~250 GtCO₂ remaining for 50% chance of staying below 1.5°C — about 6 years at current emissions levels (Lamboll et al. 2023, Nature Climate Change).
For 50% chance of 2°C: ~1220 GtCO₂, about 30 years at current levels.
At current trajectory, the 1.5°C budget would be exhausted by ~2029 (MCC Carbon Clock).

Since 1751, ~1.5 trillion tonnes CO₂ emitted globally.
USA: ~400 billion tonnes (~25% of historical total) — more than any other country.
EU countries: ~20% of historical emissions.
China: second-largest historical contributor (~13%).
Africa's regional contribution is very small relative to population.
The average American emits in ~2 days what a person in Mali or Niger emits in a year.

The global remaining budget must be divided among nations, requiring value judgments about equity.
Four principles for allocation (Ringius et al. 2002):
1. Common but differentiated responsibilities (UNFCCC) — historical emitters bear greater responsibility
2. Egalitarian — equal per-capita rights to emit
3. Sovereignty/grandfathering — proportional to current emissions (favors developed countries)
4. Ability to pay — richer countries take larger cuts
The Paris Agreement nationally determined contributions (NDCs) do not add up to the remaining carbon budget — there is a well-documented "emissions gap" (UNEP Emissions Gap Report).

The atmosphere is a finite waste sink being used without a binding global agreement on how to share it.
Unlike orbit (debris tracked physically), the atmospheric commons is tracked through national inventories, estimates, and models — with significant uncertainties.
China's emissions were overestimated by ~10% in 2013 due to using global average emission factors rather than domestic coal carbon content (Liu et al. 2015, Nature).
Global uncertainty in CO₂ emissions estimates: 2-5%.
The "carbon imbalance" in the Global Carbon Budget represents the gap in understanding of sources and sinks.

The atmosphere is a frontier commons being partitioned (by emissions allocation, carbon markets, offset schemes) before it is fully counted — the counting is the carbon budget itself, and the governance gap is the failure to agree on how to allocate the remainder.

The remaining carbon budget for 1.5°C (50% probability) was ~250 GtCO₂ as of January 2023, equivalent to ~6 years of emissions at current levels. [src: Wikipedia carbon budget / Lamboll et al. 2023]
The USA has emitted ~400 billion tonnes CO₂ since 1751, approximately 25% of all historical emissions — more than any other country. [src: Our World in Data / CDIAC]
The carbon budget must be allocated among nations via value judgments about equity; four competing principles (common but differentiated responsibility, egalitarian, sovereignty, ability to pay) produce radically different national budgets. [src: Ringius et al. 2002 / Wikipedia carbon budget]
National emissions inventories have meaningful uncertainty: China's 2013 emissions were overestimated by ~10% by using global average emission factors instead of domestic coal carbon content. [src: Liu et al. 2015, Nature]
The atmosphere, like orbit, is a finite commons being used without a binding global agreement on how to share it — the "counting" (carbon budget) is done by science, the "governance" (allocation) is done by politics, and the gap between them is the story. [synthesis]

The remaining carbon budget for 1.5°C (50% probability) was ~250 GtCO₂ as of January 2023, equivalent to ~6 years of emissions at current levels. src

The USA has emitted ~400 billion tonnes CO₂ since 1751, approximately 25% of all historical emissions. src