Kyoto University quantitatively analyzes how the international burden of climate action should be shared

The Paris Agreement sets a long-term goal of keeping the global average temperature rise well below 2℃ above pre-industrial levels and pursuing efforts to limit it to 1.5℃. In response, not only developed countries but also many developing nations have announced targets to achieve net-zero emissions (carbon neutrality) by the middle of this century. However, the economic impacts of these net-zero emissions targets on developing countries, as well as possible measures to ease the burden, had not previously been well understood.

A research team led by Professor Shinichiro Fujimori of the Graduate School of Engineering, Kyoto University, which consisted of researchers from Kyoto University, Ritsumeikan University, the National Institute for Environmental Studies (NIES), and Nagoya University, analyzed the net-zero emissions targets of countries around the world, examining both the scale of the economic burden these targets place on developing countries and the international options available to ease that burden.

The study used AIM (Asia-Pacific Integrated Model), an integrated assessment model (IAM) capable of simultaneously considering energy, land use, the economy, and household consumption behavior. This simulation model takes various socioeconomic inputs—such as future population, economic growth, advances in energy technology, renewable energy costs, food preferences, and land-use policies. Thereby, the model can analyze energy consumption, CO₂ emissions, changes in land use, and the economic impacts of emissions reductions in an integrated manner.

The research group applied this model on a global scale and analyzed three cases as long-term future scenarios which were all premised on limiting global warming to approximately 2℃.

In the scenario where each country achieves its own domestic net-zero target (Case A), household consumption in developing countries would fall by approximately 10% by 2050, while the decline in developed countries would be limited to around 3%. This means that if each country meets its net-zero target on its own, households in developing countries would face a significantly larger reduction in spending power than those in developed countries.

In the scenario where developing countries are exempted from reducing emissions and developed countries compensate through CO₂ removal (Case B), the household consumption loss in developing countries would be capped at around 3% at most. However, the required volume of CO₂ removal would reach approximately 30 gigatons per year, a very large scale equivalent to roughly three-quarters of current global CO₂ emissions, causing household consumption losses in developed countries to reach up to 12% (approximately 8% on average over the period).

In the scenario where developing countries maintain their net-zero targets while receiving financial support from developed countries (Case C), the economic losses for both developed and developing countries would be roughly comparable to those in Case B. However, the required volume of CO₂ removal would be capped at approximately 8 gigatons per year at most, demonstrating that heavy reliance on large-scale CO₂ removal could be significantly reduced.

The findings of this study indicate that a realistic pathway toward achieving global net-zero emissions in a sustainable way is for developing countries to steadily advance their emissions reductions while having the associated economic burden alleviated through international financial support.

This study was based on net-zero targets and assumed that climate stabilization would be held at approximately the 2℃ target after net-zero is achieved. Future research is expected to examine what the situation would look like under climate stabilization equivalent to the 1.5℃ target. Reaching the 1.5℃ target would require going beyond net-zero and deploying large-scale CO₂ removal. This will necessitate discussion about which countries should bear how much of that burden—and addressing these unresolved questions will be essential.

The study was published in Communications Earth & Environment.

Fujimori commented: "International efforts to address climate change are currently in a state of disunification due to a convergence of various factors. The United States' withdrawal from the Paris Agreement and policy developments in Europe in the context of the situation in Ukraine have introduced instability into the progress of international discussions. Yet the fundamental challenge that has persisted for decades—namely, how to engage developing countries in climate action while at the same time acknowledging the burden this places on them—remains unresolved. This study has quantitatively demonstrated the economic impacts of net-zero targets on developing countries and highlighted the importance of international financial support. We hope that these findings will contribute to advancing discussions toward more realistic and equitable international climate policy."

Journal Information
Publication: Communications Earth & Environment
Title: International financial support to achieve the net-zero emissions goal could help resolve equity trade-off between developing and developed countries
DOI: 10.1038/s43247-026-03208-5