Policy Brief n.49 - Global Solidarity Levies to Finance the Low-Carbon Transition: From Theory to a Practical Negotiation Tool

The provision of climate finance from developed to developing countries is a pivotal issue in international climate negotiations. At COP29 in 2024, countries agreed that developing economies – excluding China – require USD 1.3 trillion annually by 2035 in external climate finance to meet climate mitigation needs. It is increasingly recognized that traditional solutions – relying on approaches such as global carbon pricing and official development assistance (ODA) – will not suffice to reach this target at the speed needed, due to various political economy constraints and a context of weakened multilateralism. 

In this context where innovative financing is essential, this policy brief focuses on one potential avenue: Global Solidarity Levies (GSLs). GSLs are internationally coordinated but nationally administered taxes, earmarked for financing global public goods such as climate mitigation and adaptation, especially in vulnerable developing countries. As such, they could generate revenues on their own and, if spent wisely, leverage additional private capital – thereby forming part of a broader, comprehensive strategy to achieve the USD 1.3 trillion target. GSLs are increasingly discussed in international climate negotiations following the creation in 2024 of a Coalition for Solidarity Levies, which comprises 14 countries.  

To support negotiations around GSLs, we developed a simulator¹ that estimates the revenues that could be generated from three technically and politically feasible levies linked to high-emission sectors: (i) maritime shipping, based on the fuel used; and international aviation, based on (ii) fuel used and (iii) air passenger tickets. 

The simulator will enable users – including international climate negotiators – to test combinations of participating countries, tax rates and demand responses (how activities may shrink after taxation), based on publicly available data and transparent assumptions.  

Our own simulations indicate that GSLs implemented worldwide on maritime shipping and aviation could raise significant revenues: from USD 100-150 billion per year under conservative assumptions, and up to at least USD 400 billion under relatively ambitious scenarios. These amounts represent between 10% and 30% of the USD 1.3 trillion annual target. 

In today’s fractured geopolitical landscape, smaller coalitions can also remain impactful. For instance, EU member states could generate significant funds – USD 41 billion under moderate assumptions and up to USD 140 billion under more ambitious scenarios – representing over 10% of the USD 1.3 trillion target.  

Beyond a technical tool, the simulator is a negotiation instrument. By quantifying who contributes, who benefits, and by how much – while factoring in potential leakages due to loss of competitiveness – it strengthens coalition-building and credibility in climate finance discussions. Future work could extend the simulator to include additional levies, such as financial transaction, cryptocurrency, wealth, or fossil-fuel production taxes. 

¹A simplified version of the simulator (only for aviation) is available here: https://solidaritylevies.org/simulator/. A more detailed version of the simulator (covering aviation and maritime, and financial transaction levies) with access to all underlying data and demand responses, is available here: https://docs.google.com/spreadsheets/d/1tBrByrtBXkKt90xafdojeEzwIbj32aZ0/edit?usp=sharing&ouid=10298973793468 3895397&rtpof=true&sd=true