Question 1

What is a carbon budget?

Accepted Answer

The carbon budget is the maximum amount of additional CO₂ humanity can emit while keeping warming below a given temperature target (such as 1.5°C or 2°C above pre-industrial levels). It rests on the near-linear relationship between cumulative CO₂ emissions and peak warming, called the Transient Climate Response to Cumulative Emissions (TCRE), about 0.45°C per 1000 GtCO₂.

Question 2

How much carbon budget is left for 1.5°C?

Accepted Answer

As of January 2026, the remaining carbon budget for a 50% chance of staying below 1.5°C is approximately 140 GtCO₂ (Lamboll et al. 2023, updated). At current emissions of ~37 GtCO₂ per year, that's roughly 3.8 years. For a 67% chance, the budget is even smaller — around 80 GtCO₂.

Question 3

Why does the 1.5°C target matter?

Accepted Answer

The 1.5°C target was adopted in the Paris Agreement as the more ambitious limit because impacts scale non-linearly with warming. Compared to 2°C, staying at 1.5°C means roughly half as many people exposed to water stress, ten times less marine biodiversity loss, far less ice-sheet destabilization, and a near-complete saving of coral reefs versus near-total loss at 2°C.

Question 4

What does net zero by 2050 require?

Accepted Answer

Net zero by 2050 requires global CO₂ emissions to fall roughly linearly from ~37 GtCO₂/yr today to zero by 2050 — about 6–7% reductions per year. This is the central pathway in the IPCC's 1.5°C scenarios. Achieving it requires rapid electrification, renewable build-out, deep efficiency, agricultural and land-use change, and some carbon dioxide removal (CDR).

How much CO₂ is left before 1.5°C?