Frequently asked questions

The goal is to inform everyone about the consequences of one's view on fairness and requirements of climate targets. The calculations in this tool act as a 'mirror' to reflect on how the ambition gap can be closed and evaluate NDCs in light of fairness.

The results are all about allocating emissions to countries based on various principles of fairness. The tool focuses on the mitigation part of climate change. This exercise is therefore also referred to as 'burden-sharing' or 'effort-sharing' in the race to climate neutrality: it describes how the burden of reducing emissions can be shared among countries in a fair manner.

Three core principles of fairness are identified in scientific literature: (1) responsibility, taking into account historical emissions, (2) capability, emphasizing a country's financial and institutional means to implement mitigation, and (3) equality, where person on Earth gets equal allocations. For comparison and as a reference, we include the principle of continuity. These principles are subsequently quantified using mathematical formula: so-called allocation methods such as 'per capita' and 'ability to pay'.

Emissions are indicative for the general burden of climate policy, but clearly not the only aspect of just transitions. The costs of climate policy and welfare, loss and damages due to climate change, negative emissions, various sustainable development goals (SDGs) are important considerations of a just transition to climate neutrality, reaching far beyond emission allocations only. We hope this tool is a step in the right direction and hope to complement this further in the future.

The global carbon budget, or remaining carbon budget (RCB) is the maximum amount of CO₂ that can be emitted to remain with a certain maximum level of warming. Although conceptually relatively simple, there are many uncertainties involved. These uncertainties are captured by the 'Risk' slider in this tool, which captures the various estimations of the temperature response to CO₂. Note that this budget is expressed in CO₂ emissions, while most figures in this tool are computed for all greenhouse gases. It only makes sense to talk about a budget in terms of cumulative CO₂ emissions, because CO₂ remains in the atmosphere for a long time, while other greenhouse gases are mostly short-lived and filtered out quickly from the atmosphere, so it matters when exactly these greenhouse gases are emitted. The global carbon budget numbers are taken from Forster et al. (2023), who summarize updates of the WGI and WGIII reports of the IPCC, and updates of climate emulators. This update involved more stringent numbers of the global carbon budget than earlier reported. The authors also wrote a blog on Carbon Brief about this, going in more detail into the topic.

The global carbon budget (in turn dependent on the slider settings) is used to filter climate mitigation scenarios from the IPCC Sixth Assessment Report scenario database, which is a collection of over 2000 long-term mitigation pathways. The filtered pathways that are associated with the budget are used to define the curvature of the CO₂ part of the global emissions pathway, for different values of negative emissions. The non-CO₂ part of the global emissions pathway is based on estimations of Forster et al. (2023). The negative emissions slider is based on percentiles of 2100 emissions in IPCC AR6 WGIII scenarios.

There are multiple methodologically distinct ways of allocating global emissions. We allocate global emissions year by year. For example, the 'per capita' allocation method distributes global emissions of a given year based on population distributions. This is similar to the temporal allocations done in Van den Berg et al. (2019)., for example, but different from the budget-based (and subsequent linear projection of) allocation in Fekete et al. (2022).

For future population and GDP data, we used the Shared-Socioeconomic Pathways database, containing five socioeconomic scenario projections. For past population data, we used UN population data. For historical emissions, we used the PRIMAP database. For data on the global carbon budget, non-CO₂ and global emission pathways, we used Forster et al. (2023) and the AR6 scenario database. For NDC data, we use the PBL Climate Pledge NDC tool.

Below, we briefly describe the methods one-by-one. For more details, the reader is referred to earlier work by Van den Berg et al. (2019).

The 'Per Capita' method uses a country's population share in the global population and allocates future emissions accordingly. Naturally, the socio-economic scenario affects this method. All five SSPs are used in our analysis.

'Grandfathering' is a method that preserves current emission fractions. In other words, all countries reduce their emissions proportional to their current share.

The 'Per Capita Convergence' method starts as Grandfathering, but converges over time to a Per Capita basis. An additional important parameter here is the year at which this convergence completes.

The 'Ability to Pay' method allocates emissions inversely related to the GDP per capita of countries. Also this method is dependent on the socio-economic scenario.

The 'Equal Cumulative Per Capita' method computes a debt or surplus based on historical emissions and historical population, and pays off this debt (or surplus) over time, converging to a Per Capita allocation (default in 2050).

The 'Greenhouse Development Rights' method is, in the short run, based on a Responsibility-Capability Index, and in the long run based on GDP per capita (similar to Ability to Pay).

Many countries indicate NDC targets at different levels or conditional on, for example, certain developments such as economic growth or international support. The two values shown are the minimum and maximum derived NDC values.

When NDCs area published by countries, they are often expressed in relative terms (e.g. 30 % reduction in 2030 compared to 1990). The absolute values are calculations that depend on the historical and baseline emission data used. We use NDC data based on the data we use for the Carbon Budget Explorer (Jones et al., 2021), which is deduced from PBL NDC tool, which is based on historical data from PRIMAP. All NDC values are only an indication. When precise NDC data is needed, it is better to refer to the official NDC documents.

European Member States have a joint NDC, which is to reduce GHG emissions by at least 55 % by 2030 compared to 1990 levels. This is a shared goal for the EU27, and therefore no individual NDCs are available for European Member States.

The allocation of emission reductions to each Member State is determined via several Directives (ETS, ESR and others). You can find more information here.

All questions, comments and ideas are welcome. Please contact dr. Mark Dekker from the Netherlands Environmental Assessment Agency.

For general purposes, feel free to refer to this work as Dekker, M.M. (2023) The Carbon Budget Explorer. [Online]. Available: https://www.carbonbudgetexplorer.eu.

For scientific purposes, you can refer to the preprint of this work. It is currently under review.

All data can be downloaded from Zenodo, including more recent developments. Version 0.4.2 is used in the current release of the Carbon Budget Explorer. The Python code for the computations can be found on Zenodo or GitHub.

The Explorer is constantly in development, by updating NDC or other data, but also in terms of layout. If you have any ideas of improvement, please feel free to contact us.