Fair share

This element of the rating evaluates the level of effort of a government’s target or policies against what could be considered a "fair share" contribution to the global effort in reducing greenhouse gas emissions.

Although there are no agreed guidelines on what would constitute a fair level of contribution to the global effort, beyond the general understanding of reflecting the “common but differentiated responsibilities and respective capabilities, in the light of different national circumstances” (Paris Agreement, Article 4.3), governments are expected to provide some justification of their proposed efforts.

The Paris Agreement envisages an iterative approach to updating and progressing NDCs, in which individual government efforts are to be regularly revised, informed by a regular global stocktaking process.

The Climate Action Tracker (CAT) provides a way of comparing targets and action with the many interpretations of what could be considered “fair.” We hope that it helps governments, the media and observers to interpret the commitments of countries under the Paris Agreement.

The Climate Action Tracker’s “fair share range” rating system is based on published scientific literature (see below) on what a country’s total contribution would need to be to make a fair contribution to implementing the Paris Agreement, supplemented by own analysis to close data gaps.

Assessing what is fair depends on the viewpoint and interests of governments. Many consider it fair that those who have made a bigger contribution to the problem, or who have a higher capability to act, should do more.

In our assessment, we have compiled a wide range of literature on what different researchers from many perspectives would consider a “fair” contribution to greenhouse gas reductions: so-called effort sharing studies.

The effort-sharing studies in the CAT’s database include over 40 studies used by the 5th Assessment Report of the IPCC (chapter 6 of WG III, Höhne et al. (2013)), new studies that have been published since, and additional analyses the CAT has performed to complete the dataset. A full overview of the studies used is in the references list below. They cover very different viewpoints of what could be fair, including considerations of equity such as historical responsibility, capability, and equality. We take into account results from studies that are originally compatible with the former 2°C goal, as well as the 1.5°C limit in the Paris Agreement, to cover the full range of perspectives and historical developments of the long-term temperature goals.

We construct a “fair share range” for each country from the range of fairness estimates from the literature. We further use a weighting scheme to make sure that all equity viewpoints (categories) are considered equally. The fair share boundaries are chosen as the inner 90% of the study distribution. By doing so, we limit the influence of extreme studies while having the wide majority of studies included in the fair share range. We then divide the “fair share range” into sections, or ratings, by taking the same level within that range for all countries. This allows to define the same level of ambition for all countries with regards to their individual fair share literature and determine fair emission allowances in the years 2025, 2030 and 2050.

Each possible level corresponds to the temperature outcomes that would result if all other governments were to put forward targets with the same relative position on their respective fair share range, i.e. the same ambition level.

Finally, the CAT identifies which levels of same ambition on the global range lead to global warming levels relevant for the Paris Agreement:

• Critically insufficient (peak warming over the 21st century above 4˚C)
• Highly Insufficient (peak warming over the 21st century below 4°C with a 66% chance)
• Insufficient (peak warming over the 21st century below 3°C with a 66% chance)
• 2°C compatible (peak warming over the 21st century below 2°C with a 66% chance)
• 1.5°C compatible (limited end-of-century warming below 1.5°C with a 50% chance in 2100)

For example, if all governments were to put forward targets and policies at the top of their “Insufficient” range, warming would reach 3°C by the end of the century with a two-thirds chance.

An “Insufficient” rating therefore means that although the target could be considered fair by some approaches, it is not sufficient to hold warming below 2°C, much less 1.5°C, unless others do substantially more.

If all governments were to put forward targets within the “Almost sufficient” category, warming could be held below 2°C with a likely probability (66% or greater), but not “well below 2°C” or below 1.5°C.

If all governments put forward “1.5°C Paris Agreement compatible” NDCs, which is close to the most ambitious end of their “fair share range” (minimum fair emissions), warming would be held well below 2°C and limited to 1.5°C.

If all governments were to follow a “Highly insufficient” ambition level, warming would reach above 3°C and below 4°C.

If all governments were to follow a “Critically insufficient” ambition level, warming would exceed 4°C.

There are approaches that indicate a fair contribution of some countries would involve very steep reductions, in some cases going to less than zero by 2030. In cases where such stringent reductions could not be achieved domestically, the country would have to compensate what it cannot reduce within its own borders elsewhere, for example through providing climate finance to support emissions reductions in other countries.

The CAT rating of governments’ NDCs and policies against their “fair share” contribution towards reducing emissions from fossil fuel combustion, industry, agriculture and waste sources—in effect on their contribution towards long-term decarbonisation—is excluding LULUCF. The reasoning behind this approach can be found here.

Taking all published effort sharing approaches into account

For each country and year, we show the ranges that result from seven specific effort sharing categories summarised in the figure below, based on the definitions used in the 5th Assessment Report of the IPCC (chapter 6 of WG III). They cover a broad spectrum of views, but we acknowledge that some views are not quantified at this stage, such as intergenerational equity or analysis according to consumption-based emissions.

Categories of effort sharing approaches (Höhne, den Elzen, & Escalante, 2014). Note: cost effectiveness is a concept included in the capability/costs category, but isn’t a stand-alone category.

Each category puts an emphasis on one particular aspect of effort-sharing and can therefore result in (very) different outcomes from the other categories:

Responsibility: emissions reductions below a reference are determined by the level of a country’s historical emissions. This was first proposed by Brazil in the Kyoto Protocol negotiations.

Capability/Need: emissions reductions below a reference are determined by a country’s level of economic capability, often measured by GDP/capita or the Human Development Index.

Equality: emissions per capita converge to, or immediately reach, the same level for all countries

Equal cumulative per capita emissions: emissions need to be reduced so that cumulative emissions per capita reach the same level

Responsibility/capability/need: a range of studies have explicitly used responsibility and capability and the right to development as the basis for distributing emissions reductions

Capability/cost: a range of studies use equal costs or welfare loss per GDP as a basis. This is essentially a combination of mitigation potential and capability

Staged: a suite of studies have proposed, or have analysed, approaches where countries take differentiated commitments in various stages. Categorisation to a staged group and the respective commitments are determined by indicators using many equity principles

The “fair share range” of a country is determined by “walking” (or moving along) the distribution. The distribution is constructed such that each category (not each data point) has equal weight (see figure below). After weighting each category equally, we start walking the datapoints from the minimum to the middle until we have covered 5% of the weighted distribution - this point determines the lower end of the fair share range (red dotted lines in the figure below). We then keep walking until we have covered 95% of the weighted distribution – this point determines the top end of the fair share range. In this example, the fair share range is substantially smaller than the full range of all results, as some individual studies are substantially higher or lower than the rest of the dataset.

Demonstration of fair share range construction for an example country. Literature-based estimates for fair emission allowances are shown according to their equity category (a). Squares indicate studies related to 1.5C warming, while circles depict 2C studies. The symbol size reflects the weighting of studies that enforces that all studies in one category sum up to the same value. The lower panel (b) depicts the Cumulative Distribution Function (CDF) according to the same weighting as the black line. The dotted red and grey lines depict CDF of uniform distributions between the fifth and the 95th percentile and respectively the minimum and maximum.

The CAT updated its rating method in September 2021, including methodological updates to the fair share ranges for each country. In comparison to the old method we have added new studies and removed outdated ones, and adapted the way to determine the boundaries of the fair share range.

A description of the previous rating method is available here. A description of the main implications of the rating method change is available here. The CAT also updated its fair share method in 2017. For further information on how the 2017 methodology update affects our rating system click here.

We used the following literature to determine the “fair share range”:

• Baer, P., Athanasiou, T., Kartha, S., Kemp-Benedict, E., 2008. The Greenhouse Development Rights framework. The right to development in a climate constrained world. Berlin.
• Berk, M.M., den Elzen, M.G.J., 2001. Options for differentiation of future commitments in climate policy: how to realise timely participation to meet stringent climate goals? Clim. Policy 1, 465–480.
• Bode, S., 2004. Equal emissions per capita over time - A proposal to combine responsibility and equity of rights for post-2012 GHG emission entitlement allocation. Eur. Environ. 14, 300–316. https://doi.org/10.1002/eet.359
• Böhringer, C., Welsch, H., 2006. Burden sharing in a greenhouse: Egalitarianism and sovereignty reconciled. Appl. Econ. 38, 981–996. https://doi.org/10.1080/00036840500399453
• Bows, A., Anderson, K., 2008. Contraction and convergence: an assessment of the CC Options model. Clim. Change 91, 275–290. https://doi.org/10.1007/s10584-008-9468-z
• Chakravarty, S.P., Chikkatur, A., Coninck, H., Pacala, S., Socolow, R., Tavoni, M., 2009. Sharing global CO2 emission reductions among one billion high emitters. Proc. Natl. Acad. Sci. USA 106, 11884–11888.
• Criqui, P., Kitous, A., Berk, M., den Elzen, M.G.J., Eickhout, B., Lucas, P., van Vuuren, D.P., Kouvaritakis, N., Vanregemorter, D., 2003. Greenhouse gas reduction pathways in the UNFCCC Process up to 2025 - Technical Report. Grenoble; France.
• den Elzen, M.G.J., Beltran, A.M., Hof, A.F., van Ruijven, B., van Vliet, J., 2013. Reduction targets and abatement costs of developing countries resulting from global and developed countries’ reduction targets by 2050. Mitig. Adapt. Strateg. Glob. Chang. 18, 491–512. https://doi.org/10.1007/s11027-012-9371-9
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• Holz, C., Kartha, S., Athanasiou, T., 2017. Fairly sharing 1.5: national fair shares of a 1.5 °C-compliant global mitigation effort. Int. Environ. Agreements Polit. Law Econ. https://doi.org/10.1007/s10784-017-9371-z
• IPCC, 2018. Summary for Policymakers, in: Masson-Delmotte, V., Zhai, P., Pörtner, H.O., Roberts, D., Skea, J., Shukla, P.R., Pirani, A., Moufouma-Okia, W., Péan, C., Pidcock, R., Connors, S., Matthews, J.B.R., Chen, Y., Zhou, X., Gomis, M.I., Lonnoy, E., Maycock, T., Tignor, M., Waterfield, T. (Eds.), Global Warming of 1.5°C. An IPCC Special Report on the Impacts of Global Warming of 1.5°C above Pre-Industrial Levels and Related Global Greenhouse Gas Emission Pathways, in the Context of Strengthening the Global Response to the Threat of Climate Change,. World Meteorological Organization, Geneva, Switzerland, p. 32.
• Jacoby, H.D., Babiker, M.H., Paltsev, S., Reilly, J.M., 2008. Sharing the Burden of GHG Reductions. Massachusetts; USA.
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