Using net-zero carbon debt to track climate overshoot responsibility

Area of Science:

• Climate Science
• Environmental Policy
• Climate Equity

Background:

• Current emissions trajectories project the depletion of the 1.5 °C carbon budget around 2030, leading to a temporary overshoot.
• Understanding regional responsibilities for exceeding this budget is crucial for effective climate action and equity.

Purpose of the Study:

• To introduce and apply the concept of 'net-zero carbon debt' to quantify future responsibilities for carbon budget exceedance.
• To inform the scale of carbon drawdown obligations and regional responsibilities for increased extreme heatwave exposure.

Main Methods:

• Analysis of vetted mitigation scenarios from the IPCC Sixth Assessment Report and current policy/pledge scenarios.
• Application of an equal per capita allocation of the remaining 1.5 °C carbon budget from 1990.
• Calculation of regional 'net-zero carbon debt' based on projected budget breaches at net-zero emissions.

Main Results:

• Quantification of regional carbon debt, indicating the extent to which each region is expected to exceed its fair share of the carbon budget.
• Estimation of necessary carbon drawdown obligations for regions to address budget exceedance.
• Assessment of relative regional responsibilities for increased lifetime exposure to extreme heatwaves due to budget overshoot.

Conclusions:

• The 'net-zero carbon debt' metric provides a forward-looking approach to climate responsibility and effort-sharing.
• Findings highlight the need for robust climate equity considerations and mechanisms that extend beyond the exhaustion of the carbon budget.
• This research strengthens intergenerational equity in climate discourse and informs practical implementation of climate mitigation strategies.