Thomas Hahn is associate professor at the Stockholm Resilience Centre and research leader for FAIRTRANS. Robert Höglund is a carbon removal advisor with Marginal Carbon. Mikael Karlsson is associate professor at Uppsala University and research leader with FAIRTRANS. 

Recent news articles, in the Guardian and from Bloomberg among others, have proclaimed the death of the 1.5°C target given how emissions and lack of sharper commitments are developing. In a new study, in Nature Communications we examine how the responsibility to limit long-term warming to 1.5°C could be allocated after a temporary overshoot, if countries are held accountable in line with the principle of Common But Differentiated Responsibility and Respective Capabilities (CBDR-RC) as established under the UNFCCC.

This principle, a cornerstone of climate diplomacy, recognizes that while all countries share responsibility for addressing climate change, their obligations differ based on historical emissions and capacity to act. By comparing countries’ past emissions and future emission claims with their equal cumulative per capita emissions, we establish a new indicator – “additional carbon accountability” – showing countries’ responsibilities beyond current climate targets.

If existing national climate targets are met, the 1.5°C fossil carbon budget (for a 50% probability of meeting that goal) will be exceeded with 576 billion tonnes of carbon dioxide (GtCO₂). To meet the 1.5°C target, our indicator shows that the EU, China, the US, and 15 other countries must sharpen their own current targets with faster mitigation and more carbon dioxide removal (CDR), such as afforestation and technical solutions like direct air capture and biochar. All other countries must stick to their national climate plans (nationally determined contributions – NDCs) and net-zero targets.

Counting future emissions

As an example, the EU would need to mitigate or remove an additional 48 GtCO₂ or finance additional reductions beyond current targets in other countries, on top of reaching its own targets in terms of the NDC for 2030 and net zero emissions by 2050. For China, the additional carbon accountability is 150 GtCO₂ and for the USA 167 GtCO₂.

While there is no international agreement on how to operationalize the fairness principles of the Paris Agreement, the new indicator – based on the CBDR-RC – provides an important tool to clarify what different countries are accountable for in relation to the mitigation (emissions) gap. This information feeds directly into the contested annual negotiations on climate financing within the UNFCCC COP meetings.

In general, high-income countries have large carbon debts, while several of the BRICS and upper-middle-income countries have high planned future emissions. Much focus of climate advocacy has been on getting high-income countries to reduce their emissions. Of planned future emissions, 26% come from high-income countries, but as much as 38% comes from upper-middle-income countries with an additional carbon accountability.

China and Iran, for example, have plan