Imagine a government pledging billions to save the planet while simultaneously spending even more to subsidize the very fossil fuels accelerating climate change. For decades, national budgets have operated like a fiscal “black box,” where high-level climate commitments and spending decisions rarely align. Governments speak the language of the Paris Agreement and Sustainable Development Goal 13 (Climate Action), but without a mechanism to track public expenditure, these commitments risk remaining little more than paper promises.

The stakes have never been higher. Human-induced climate change intensified further in 2025, with several impacts now considered irreversible for centuries to come. As the Sustainable Development Goal Report 2025 highlights, limiting long-term warming is still possible, but only if climate objectives are translated into coordinated fiscal action.

Public budgets, and not policy declarations, ultimately determine whether mitigation and adaptation efforts succeed.

This gap between ambition and allocation has given rise to Green Budgeting, commonly implemented through Climate Budget Tagging (CBT). By systematically identifying and classifying climate-relevant public expenditures, CBT opens the fiscal black box, allowing governments to assess whether budgetary decisions support their climate goals or undermine them.

A solid classification system is key to ensure green budget tagging has a meaningful impact on informed decision making and resource allocation. One widely used classification framework to guide green budget tagging is the French local mitigation methodology developed by I4CE. It rates actions based on their impact on climate mitigation as highly favourable, favourable (green), neutral (grey) or unfavourable (brown).

The Problem and the Policy: Why Was It Started?

The primary driver for Green Budgeting has been persistent policy incoherence. Governments frequently find themselves in a fiscal paradox: the Ministry of Environment would receive funding for reforestation, while the Ministry of Finance simultaneously provided tax concessions or subsidies to activities that encouraged deforestation, fossil fuel use, or carbon-intensive growth.

CBT emerged to address three core governance failures:

Transparency deficits. Policymakers lacked a comprehensive inventory of how much public spending supported climate objectives versus how much of it actively undermined them. Without this visibility, climate commitments remained detached from financial reality.

Isolated climate responsibility. Climate action was often confined to environment ministries, despite the fact that transport, energy, agriculture, and urban development ministries control the bulk of climate-relevant spending. Budget tagging forces these line ministries to explicitly identify, justify, and finance their role in the climate transition.

Accountability and greenwashing risks. In the absence of standardized definitions, governments could label expenditures as “green” without credible evidence of climate impact. CBT introduces common classification frameworks that make climate claims verifiable rather than rhetorical.

Longevity and Sustainability: From Pilot to Public Finance Tool

Climate Budget Tagging is no longer a theoretical experiment. Developed in 2012 with support from the UNDP and the World Bank, CBT builds on earlier experience with poverty and gender-responsive budgeting. Following the world’s first Climate Budget in Nepal in 2013, tagging systems have since been institutionalized in at least 19 national and subnational governments, particularly across the Asia-Pacific region.

What has sustained these initiatives is their integration into existing budget cycles. Rather than creating parallel climate funds, CBT retools existing expenditure classification systems, embedding climate considerations within routine processes. While implementation is not costless, the scale and long-term nature of climate finance mean that the benefits of improved transparency and coordination far outweigh the initial administrative investment.

For developing countries, this function is especially critical. Although they have contributed least to historical emissions, they are among the most vulnerable to climate impacts and will account for a large share of required global mitigation. International climate finance is intended to bridge this equity gap, but access to such finance increasingly depends on credible fiscal data. CBT allows governments to “package” public investment programs for external partners, providing the transparency and accountability that donors and investors demand.

The Transparency Paradox: What Climate Budgets Still Miss

Despite its promise, CBT has exposed a significant transparency paradox.

The brown spending blind spot: To date, almost no country publishing a climate budget has comprehensively disclosed environmentally harmful expenditures. Climate reports overwhelmingly focus on “green” spending, while subsidies and tax expenditures supporting fossil fuels or other carbon-intensive activities remain largely invisible. France stands out as a rare exception, having integrated adverse environmental impact tags into its 2021 budget, offering a more balanced picture of fiscal alignment.

The green bond disconnect : Dozens of countries issuing sovereign green bonds are contractually required to provide private investors with detailed disclosures on project selection, expenditure tracking, and environmental impact. Ironically, this means governments often offer greater transparency to international capital markets than to their own legislatures and citizens regarding the broader environmental footprint of public spending.

This asymmetry limits CBT’s ability to inform genuine trade-offs and risks reducing climate budgeting to a selective reporting exercise rather than a tool for fiscal reform.

Does It Deliver? Evidence from Early Adopters

Ultimately, the credibility of Green Budgeting depends on outcomes, not classification alone. Early adopters suggest that when designed well, CBT can shift how governments understand and prioritize climate finance.

France : By tagging its 2023 Finance Bill, France identified €38 billion in environmentally favorable spending, but also €7 billion in environmentally unfavorable expenditures, including diesel tax concessions in agriculture and transport. Making these trade-offs visible provided reformers with a concrete basis for subsidy reform.

Indonesia :  Budget tagging revealed that existing allocations covered only 38 percent of the country’s estimated climate financing needs. This evidence enabled the government to recalibrate planning and aggressively pursue external financing to address the remaining gap.

Odisha, India : Through its Climate Change Impact Appraisal, the state identified schemes with high climate sensitivity, i.e., programs vulnerable to failure under heat stress and flooding, thus allowing infrastructure investments to be redesigned for future climate conditions.

These cases illustrate CBT’s strongest contribution: not prescribing policy choices, but clarifying the fiscal consequences of existing ones.

Conclusion: From Accounting Exercise to Climate Choice

Sustainable Development Goal 13 emphasizes the integration of climate action into national policies, planning, and institutional frameworks. As recent records show, the challenge is no longer a lack of awareness, but a lack of alignment between climate intent and public finance.

Green Budgeting offers a practical pathway to close this gap. By transforming budgets from static accounting documents into strategic climate tools, governments can move beyond symbolic commitments toward measurable action. Yet transparency alone is insufficient. For CBT to fulfil its potential, it must evolve to confront harmful expenditures alongside beneficial ones and support informed political debate about financial priorities.

Opening the fiscal black box is a necessary first step. Acting on what it reveals is the real test of climate governance in the twenty-first century.