Comparability of effort

As governments submit their emissions reduction offers during 2015, they will look at what others are doing, and decide whether it is comparable. They may all have their own interpretation of what is their fair share.

CAT gives a fully transparent way of comparing proposals with the many interpretations of what is fair. We hope that it helps governments, the media and observers to interpret the offers made in the run-up to the Paris UNFCCC conference in December where governments are expected to agree a new, global agreement to combat climate change.

New method to rate ambition

Assessing what is fair depends on the viewpoint. Some consider it fair that those who have made a bigger contribution to the problem, or have a higher capability to act, should do more. But even if that were agreed, how much more should they do?  

In our Effort Sharing assessment, we have compiled a wide range of literature on what researchers would consider a “fair” contribution to greenhouse gas reductions. The “effort-sharing” studies in the CAT’s database include over 40 studies used by the IPCC (chapter 6 of WG III and Höhne et al. (2013)) plus additional analyses the CAT has performed to complete the dataset. They cover very different viewpoints of what could be fair, including considerations of equity, including historical responsibility, capability, and equality. We only include those results from studies that are compatible with the 2°C limit.

We do not decide what is fair, but take the full rage of the estimates from the literature. On the most aggregated level we show the full range of all possible effort sharing approaches (the coloured bars in Figure 1 and Figure 2).

If a government’s proposal results in emissions above that range we rate them “inadequate” (coloured red in the bar): the proposals would be not in line with a 2°C pathway under any interpretation of what is “fair.”

If they are below that full range they are rated “role model” (dark green).  Such proposals are even more ambitious than any interpretations of what would be “fair”.

Within the full range of what could be considered “fair” we differentiate between a “medium” (yellow) and a “sufficient” (pale green) rating: if all governments were to choose the least ambitious end of the range, the aggregate of all the proposals would result in emissions well above what is required to keep warming below 2?C. Only if all governments were at the intersection of “medium” and “sufficient” - or lower - would global emissions be compatible with the 2°C limit.

Therefore a government is only rated “sufficient” if the emissions resulting from its proposal are in the lower half of the range of what could be considered as “fair”. If the emissions resulting from its proposal are in the upper half of that range they are rated “medium. Such proposals are heading in the right direction with room for improvement. 

Figure 1. The Climate Action Tracker’s rating system


In the example in Figure 2 we find that the range is substantial, in this case for 2025. It ranges from a reduction of around a few per cent below current levels to less than zero emissions. This means that in some interpretations of what is fair, this example government would have no emissions allowances left in 2030 and would have to compensate its remaining emissions with reductions elsewhere, for example through reduction projects in other countries.

Figure 2. Example illustration of the ratings (example US)

If a country is at the border between two categories, several additional elements are important in the rating:

Taking all possible sharing approaches into account

For each country and year we show full the ranges that result from specific categories of approaches (Figure 3), based on the definitions used in the IPCC report. Each category puts emphasis on one particular aspect and therefore results in different outcomes from other categories:


Using the detailed representation (see Figure 3 for an example), a user can discern the possible results of a category that he/she considers as fair.  The “medium” to “sufficient” range excludes the highest and the lowest category. E.g., this applies at the lower end to the category “equal cumulative per capita emissions” in Figure 3, which represents an outlier for this country. Also at the top end, the start of the full range is defined by the second highest category, but a difference is not visible as the first and second category start at almost the same level. For each category, we show the 10th to 90th percentile of all results, eliminating extreme outliers.



 Figure 3. Detailed results of effort sharing approaches and how they are used to construct the range for the US in 2025. The left hand graph shows the range of emission levels expected for the US under each of the seven different sharing approach categories (number of data points in brackets). The coloured bar shows the translation into the four rating categories used by CAT (inadequate, medium, sufficient, role model). The one but highest and one but lowest end of a category defines the medium plus sufficient range.








The effort sharing results based on capability/costs and capability define the top end of the range for the US in 2025 (Figure 3). According to these approaches US Government’s proposal to reduce emissions by 26–28% by 2025, resulting in a 2025 emission level of 5205-5350 MtCO2e/a, would be considered a “fair share.” These calculations assume that costs to reduce emissions in the US are high and that larger emissions reductions would have to be made by other countries for overall compatibility with a 2°C pathway.

The bottom end of the range is defined by the approaches based on equal cumulative per capita emissions and the responsibility / capability / needs category. These approaches assume that the US has used its carbon budget already and has so much responsibility and capability that it should actually have zero emissions in 2025 (if necessary compensating its real emissions with allowances from elsewhere). With this perspective the US proposal for 2025 is well outside of what is considered fair.

In general, the full range over all effort sharing categories is small for countries that are large and therefore make the average (e.g. China) or that have an average emission profile (e.g. Mexico). Effort sharing results for these countries are always average regardless of the approach. The ranges are large for countries that are small and that have a very particular emission profile (e.g. Kazakhstan or New Zealand). For these countries the choice of the effort sharing approach makes a large difference.  

Changes compared to the methodology of 2009

This update of 2015 results in different ranges compared to those calculated in 2009 and used since. This is due to two reasons.

First, we used in this update more studies and a wider range of interpretations of equity. It now includes studies for the categories “equal per cumulative per capita emissions” and “responsibility capability and need”, which usually result in very stringent reductions for developed countries, and studies in the category “capability/cost”, which usually results in less ambitious reductions for developed countries. As a result the ranges have become larger for almost all countries.

Second, as time progresses and national and global emissions change, the starting point of countries and the global level in a particular year that is consistent with the 2°C limit changes as well. For some developing countries emissions have significantly increased from 2005 (the usual staring year for effort sharing calculations of 2009) and 2010 (the usual starting year of effort sharing calculations from this update). Accordingly the allowances are likely to be higher. Also the global emission limit consistent with the 2°C limit assumed in the studies for 2020 is now higher, as emissions have increases and the world is on a delayed action pathway compared to what was assumed in 2009.


Input data

Raw data from over 40 studies (incl. list of studies in table format in Annex), as gathered for (Höhne et al., 2013). Additionally, we take into account three more sources:

The first step it to filter the data. The algorithm applies the following filters:

A few studies were excluded, either if they were too old or not all data inconsistencies could be clarified (see Annex)

Harmonisation of scope

The scope of the different studies varies in terms of sectors and gases covered. Some only cover CO2, others cover all gases. We therefore applied a method to harmonise for the scope covered (as applied in (Höhne et al., 2013).

For each study, emissions for remaining gases and sectors were added using the historic and future projected emissions from the Climate Action Tracker, if available. The CAT country assessment produces scenarios including implemented policies and mitigation targets. This does not reflect results from effort sharing calculations for these sectors. Therefore, we scale these scenarios, using the reduction of the effort sharing results below the reference scenario in the original study. This means, that we assume that the relative emission reductions in the missing sectors would be similar to those in the scope of the original study.

Where no sectoral data or a reference scenario exists, we assume that the harmonisation of the scope is covered by the adjustment of the base year value of the total emissions (see section below).

Harmonisation to base year

Independently of the scope, the studies may have different values for emissions in the starting year when the effort sharing calculations start. The models use different data sources for historic emissions. The differences can be substantial, especially for countries where the share of non-CO2 emissions is high.

The whole time series of each study and scenario is scaled upwards or downwards by one factor, so that the starting year has the same emissions value as the standard CAT dataset. For countries not covered by the Climate Action Tracker, historic data from the EVOC model serves as a common base level.

Where this option leads to drastic absolute differences between to original and the harmonised value of over 300%, we scale the whole time series by an absolute amount of emissions (not a multiplicative factor).

Calculation of the factor to differentiate between medium and sufficient

If a country would chose the top end of its the effort sharing range implies that for other would have to reduce more than their top end of the range in order to still meet the required global emissions pathway. As such, the maximum of country A does not necessarily reflect the same approach as the maximum of country B, and the sum of all maxima would be above the level required to stay on a 2° compatible pathway.

Proposing an emissions reduction target in the upper end of a country’s effort sharing range thus does not necessarily make this proposal “sufficient”. The Climate Action Tracker introduces a “medium” category to reflect this condition. A “Medium” rating means that the proposal would only be 2° compatible, if other countries moved to their more ambitious end of their effort sharing range.

We calculate the share of the medium category of the effort sharing range in the following way:



n             is the number of countries,

Emin        is the minimum of the effort sharing range of a country (the second lowest end of any category),

Emax       is the maximum of the effort sharing range of a country  (the second highest end of any category),

E2°          is the sum of all countries required for 2° compatibility and

Factor      is the share of the effort sharing range, which will be rated medium, equal for all countries


This can be solved as follows:

The table below illustrates the results of these calculations for the different years.












Annex: List of studies used in the analysis

The table below shows, which studies have been considered and which have been included in the data harmonisation exercise.

Study name

Included in harmonsiation

001 (Michel G. J. den Elzen, Beltran, Hof, van Ruijven, & van Vliet, 2013)


002 (Van Vuuren, Isaac, Den Elzen, Stehfest, & Van Vliet, 2010)


003 (Hof & Den Elzen, 2010)


004 (Knopf et al., 2009)


005 (Michel G J den Elzen, Höhne, & Moltmann, 2008)


007 (Hof & Den Elzen, 2010)


008 (Michel G J den Elzen, Lucas, & van Vuuren, 2008)


009 (van Vuuren et al., 2009)


010 (Michel G J den Elzen, Höhne, Brouns, Winkler, & Ott, 2007)


011 (Michel G J den Elzen & Meinshausen, 2006)


012 (Michel G J den Elzen, Lucas, & van Vuuren, 2005)


013 (Michel G J Den Elzen & Lucas, 2005)


014 (Criqui et al., 2003)


015 (Berk & den Elzen, 2001)


016 (Kuntsi-Reunanen & Luukkanen, 2006)

Different stabilisation level

017 (Winkler, Letete, & Marquard, 2011)

Different stabilisation level

018 (Chakravarty et al., 2009)


019 (Bows & Anderson, 2008)


021 (Vaillancourt & Waaub, 2004)

Different stabilisation level

022 (Miketa & Schrattenholzer, 2006)

Different stabilisation level

023 (Bode, 2004)

Different stabilisation level

025 (Böhringer & Welsch, 2006)


026 (Groenenberg, Blok, & van der Sluijs, 2004)

Different stabilisation level

027 (WBGU, 2009)


028 (Knopf, Kowarsch, Lüken, Edenhofer, & Luderer, 2012)

Data inconsistencies

031 (Nabel et al., 2011)


032 (Peterson & Klepper, 2007)


034 (Onigkeit, Anger, & Brouns, 2009)


035 (Jacoby, Babiker, Paltsev, & Reilly, 2008)


036 (Edenhofer et al., 2010)

Different stabilisation level

037 (Höhne & Moltmann, 2009)


038 (Höhne & Moltmann, 2008)


042 (Jayaraman, Kanitkar, & Dsouza, 2011)


043 NIES (Kriegel et al., 2014)

Data inconsistencies

044 PNNL (Kriegel et al., 2014)


045 PBL (Kriegel et al., 2014)


046 IIASA (Kriegel et al., 2014)


047 PIK (Kriegel et al., 2014)


048 FEEM (Kriegel et al., 2014)


049 (Kober, Zwaan, & Rösler, 2012)

Data inconsistencies

050 (P Baer, Athanasiou, Kartha, & Kemp-Benedict, 2008)


051 (Pan, Teng, & Wang, 2014)

Different stabilisation level

052 (Pan et al., 2013)


PRIMAP calculations


EVOC calculations




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