Possible to limit climate change to 1.5°C, if EU and 17 other countries go beyond their own targets

A new study in Nature Communications finds that limiting global warming to 1.5 °C is still possible, but some countries require support to meet their climate responsibilities. An "additional carbon accountability" indicator is introduced, revealing that the EU and 17 other countries must exceed their own current targets to achieve this global goal.

The new study proposes an indicator -- additional carbon accountability -- that quantifies countries' responsibility for mitigation and carbon dioxide removal in addition to achieving their own targets. Aside from further domestic reductions, this additional carbon accountability requires financing carbon removal, or emission reductions outside their territories.

A pressing question at the ongoing 29th annual UN Climate Conference (COP29) in Baku, Azerbaijan, is how to transition away from fossil fuels and speed up climate mitigation in line with the 1.5C global warming target. To address this, the new study by researchers from Stockholm University, Chalmers University of Technology, and Uppsala University, quantifies how much each country should reduce or remove carbon dioxide emissions beyond their current national commitments.

"The ambition of this article is to suggest opportunities to enhance climate fairness and close the mitigation gap in the real world, based on the Paris Agreement," says lead author Thomas Hahn, from the Stockholm Resilience Centre at Stockholm University.

The study quantifies each country's equal share of the remaining 1.5C carbon budget based on equal per capita historic emissions since 1990 and share of the remaining carbon budget. This is then compared to countries' actual carbon debts and future emissions targets, creating an "additional carbon accountability" indicator.

The study identifies 18 high-income and upper-middle-income countries that should be accountable for increasing their ambitions to stay within their equal per capita share of the global carbon budget for 1.5 °C. (Note that the EU is here counted as one country). Additional carbon accountability is highest for the United States and China, and highest per capita for the United Arab Emirates, Russia, Saudi Arabia and the United States.

"While there is no agreement on how to operationalize the fairness principles of the Paris Agreement, the new indicator provides an important tool to clarify the responsibility for the remaining mitigation gap in the context of the ongoing climate talks," explains co-author Johannes Morfeldt from Physical Resource Theory, Department of Space, Earth and Environment, at Chalmers University of Technology.

In general, high-income countries have large carbon debts while several upper-middle income countries have high future emissions. Four of the 18 countries could theoretically fulfil their accountability with stricter domestic emission reductions.

"14 of these 18 countries have a larger accountability than planned future emissions, meaning they would need to increase ambitions for carbon dioxide removal or for emission reductions in other countries, in addition to stricter emissions reductions," says co-author Ingo Fetzer, from Stockholm Resilience Centre, Stockholm University.

As an example, besides reaching its 2030 reduction target and net zero by 2050, the EU would need to remove an additional 48 Gt carbon dioxide (gigatonnes, or billion metric tonnes) or finance additional reductions beyond current targets in other countries. For China, the additional carbon accountability is 150 Gt and the USA 167 Gt.

"Our study shows that it's high time for the European Union to enhance its climate targets, instruments, and financing, to take responsibility for its fair share of a global carbon budget compatible with the Paris Agreement," says co-author Mikael Karlsson from Climate Change Leadership, Department of Earth Sciences, at Uppsala University.

The study shows that the ability to pay is not uniform. Several BRICS+ nations, particularly Iran and Russia, may struggle economically to meet their additional responsibilities, in contrast to G7 members.

"Our results highlight that meeting the 1.5C target to a large extent is reliant on large historic emitters like the EU and the US paying off their historic carbon debts, and countries with plans for future large emissions, like China and Iran, setting stricter reduction targets," adds co-author Robert Höglund.