Request from the lawyers of the plaintiffs in Application no. 53600/20

SUBJECT: legal case at the European Court of Human Rights (ECtHR)(KlimaSeniorinnen and Others v. Switzerland)
Issues raised by Switzerland relating to the Climate Action Tracker
April 26, 2023

Questions relating to the Climate Action Tracker

Question as received from Applicants

In its answers Switzerland states that there is “no agreed methodology for calculating a fairemissions reduction budget assigned to each country” and that “every effort to calculate nationalbudgets contains a strong element of subjectivity” referring to the studies performed by the Climate
Action Tracker, Climate Analytics and the study by Rajamani et al. (2021). In relation to the Climate
Action Tracker, Switzerland states that “the NGO Climate Action Tracker has seven specific effortsharing categories (...) the classification of countries into each of these categories is questionable
and the methodology unclear (...) on its website, the organisation itself acknowledges that there isno single agreed framework on what constitutes a fair contribution to global efforts”.
We are aware of the methodology of the CAT as described on its website including the fact thatits results are based on the assessment of effort sharing studies in the IPCC Fifth Assessment
Report (WG III, Chapter 6) and new studies and analysis since the publication of that report (asdescribed on the CAT website here: https://climateactiontracker.org/methodology/cat-ratingmethodology/fair-share/ )In addition to what is described there;
Question 1: Could you, as a member of the CAT consortium, provide a description of the CAT
consortium and the scientific underpinning of the CAT methodology? In addition, could youcomment on the specific critique of Switzerland on the CAT methodology as described here.

Response on behalf of the CAT consortium

The Climate Action Tracker (CAT) is an independent scientific project that tracks government climate
action and measures it against the globally agreed Paris Agreement aim of "holding warming well below
2°C, and pursuing efforts to limit warming to 1.5°C." The CAT was founded in 2009 and is a collaborationof two renowned research organisations: Climate Analytics and NewClimate Institute. The CAT also
receives support from the Institute for Essential Services Reform. Past consortium members haveincluded the Potsdam Institute for Climate Impact Research (2009–2016) and Ecofys, a Navigant
company (2009–2019). The CAT is funded by the Federal Government of Germany via the International
Climate Initiative, the Climate Emergency Collaboration Group via Rockefeller Philanthropy Advisors,
the ClimateWorks Foundation, and the European Climate Foundation. 47 policy, science, and modelling
experts are involved in developing and updating the CAT. Several of these experts are also IPCC authors.
CAT team members (e.g Prof. Dr. Niklas Höhne) have over 20 years scientific experience with allocating
emissions to countries based on equity principles. They prepared the meta-study and developed thecategorisation1 that was later used in several IPCC reports 2, and which forms the basis for the CAT
methodology.

The following paragraphs respond to the specific critique made by Switzerland.

Re: No agreed methodology for calculating fair shares
The UN Framework Convention on Climate Change, which is universally agreed, includes the principleof “common but differentiated responsibilities and respective capabilities”. This principle is globallyaccepted. Equity on the basis of the principle of common but differentiated responsibilities needs tobe considered regardless of the uncertainties. If a national emissions target falls outside of the fullrange of possible interpretations of equity, then it is definitely not in line with the UNFCCC and the ParisAgreement.
In addition, States cannot apply the most convenient equity approach to their own circumstances. If
each State picks the equity interpretation most preferable to it, the 1.5°C limit would be missed by asignificant margin. The unique strength of the CAT’s methodology is that it covers all major countries(80% of current emissions) and therefore can put Switzerland's targets into a global perspective andprovide an estimated global warming level.
The CAT’s methodology applies the best available science to determine a State’s fair share. The CAT
applies a synthesis framework which considers a wide range of perspectives of what could beconsidered fair, including equity principles such as historical responsibility, capability and equality, andweights them equally. This constitutes the most neutral way of combining different views of equity.
The CAT’s analysis is based on over 40 studies used by the 5th Assessment Report of the IPCC (chapter6 of WG III, Höhne et al. (2013)), new studies that have been published since, and additional analyses
the CAT has performed. The categorisation of principles used by the CAT is that developed by Höhne etal. (2014)3, which was the basis for the framework used in the IPCC’s AR5 WGIII chapter 6 on effortsharing. 23 individual studies underlie the CAT methodology, though in some instances a study provides
several different equity approaches, all of which are included in the methodology. Categories are given
an equal weighting in our framework to avoid favouring any particular equity principle over another, aswell as to develop the most thorough equity framework possible in line with the best available science.
The CAT’s methodology focuses on emissions emitted within a State’s boundaries, i.e. it pursues aterritorial approach. Thus, it should be noted that the CAT’s methodology is favourable to States suchas Switzerland, who do not have a large industry sector but instead import much of their goods andservices and thus have significant consumption-based emissions that are not considered under CAT’smethodology.

1den Elzen, M.; Höhne, N. (2008). Reductions of greenhouse gas emissions in Annex I and non-Annex I countries
for meeting concentration stabilisation targets: An editorial comment. Climatic Change, 91(3–4), 249–274. https://doi.org/10.1007/s10584-008-9484-z
den Elzen, M., Höhne, N. (2010). Sharing the reduction effort to limit global warming to 2°C. Climate Policy, 10(3),247–260. http://www.tandfonline.com/doi/abs/10.3763/cpol.2009.0678
Höhne, N., den Elzen, M., Escalante, D. (2014). Regional GHG reduction targets based on effort sharing: acomparison of studies. Climate Policy, 14(1), 122–147. https://doi.org/10.1080/14693062.2014.849452

2

IPCC WGIII, AR4, ch 13 box 13.7
IPCC WGIII, AR5, ch 6, figure 6.28 and 6.29

3

Niklas Höhne, Michel den Elzen & Donovan Escalante (2014) Regional GHG reduction targets based on effort
sharing: a comparison of studies, Climate Policy, 14:1, 122-147, DOI: 10.1080/14693062.2014.849452

2

Re: Great degree of subjectivity

Switzerland’s claim that the CAT’s analysis contains “a strong element of subjectivity” due to theassessment not reflecting “an agreed methodology for evaluating states' climate change efforts” is amisrepresentation of the CAT’s methodology.
Subjectivity is eliminated in the CAT’s approach by using a wide range of equity principles that are allweighted equally. Developing a synthesis framework of all relevant equity approaches based on thebest available science is the most objective way of establishing a state’s fair share of the global effort.
From Switzerland’s NDC, it can be followed that, in theory, Switzerland supports integrating equity
considerations into its climate targets. However, Switzerland does not provide the calculations as to
how its targets are equitable. The CAT views its methodology as building on Switzerland’s principal
support for equity by providing a mathematical basis for its fair share. This is because a State’s fair sharemust ultimately be based on modelling and mathematical calculations and not on theoretical support
for any equity methodology alone.

Re: The CAT’s methodology used to determine a State’s fair share is unclear

Switzerland claims that the classification of countries into each of the seven specific effort-sharing
categories used by the CAT is questionable and the methodology unclear. We reject this notion, as themethod is clearly described in the peer reviewed scientific literature4.
The CAT uses seven specific effort-sharing categories in line with those presented in chapter 6 of theIPCC’s AR5 WGIII. To avoid favouring any particular equity principle over another, as well as to develop
the most thorough equity framework possible according to the best available science, a synthesis
framework is applied which considers all existing relevant equity methodologies.
After weighting each equity category equally, we prevent extreme values, either at the most stringent
or least stringent end of the range, from distorting a country’s fair share range by excluding results
which fall outside the 5th to 95th percentiles. The CAT provides a demonstration of how it determines
the fair share range for each State on its website, as well as a full description of its methodology andthe list of literature used to determine the “fair share range”5.
This fair share range defines a comparable ambition level range for all countries. Thus, setting amitigation target level for all major countries at the same relative position in this range is considered an“equal level of ambition”. For each level, the CAT methodology estimates the global emission trajectory
over the century and is able to relate it to a global warming level. This finally allows the identificationof an equal level of ambition for all countries which limits global warming to 1.5°C.
A recent contribution to the literature, entitled “National ‘fair shares’ in reducing greenhouse gas
emissions within the principled framework of international environmental law”6 (hereafter referred toas “Rajamani et al.”), examines the ambition level required of countries according to principles ofinternational environmental law. The analysis relies on the same approach as the CAT , with an aim todetermine an appropriate ambition level for countries from the perspective of ensuring that the sumof individual contributions is collectively compatible with the Paris Agreement’s target. A key similarity
between the CAT’s assessments and Rajamani et al. is that both studies draw from the full spectrum ofequity perspectives provided in the scientific literature, rather than basing their analysis on a specific,

4Niklas Höhne, Michel den Elzen & Donovan Escalante (2014) Regional GHG reduction targets based on effort
sharing: a comparison of studies, Climate Policy, 14:1, 122-147, DOI: 10.1080/14693062.2014.849452

5CAT, CAT rating methodology, Fair share, available at https://climateactiontracker.org/methodology/cat-ratingmethodology/fair-share/

6

Rajamani, L., et al, National ‘fair shares’ in reducing greenhouse gas emissions within the principled framework ofinternational environmental law. Climate Policy 21(8), 983–1004 (2021)

3

more limited set of normative assumptions, as other studies do. In both cases, approaches based solely
on grandfathering or cost-effectiveness are excluded as these are not considered consistent with any
fair share principles. Rajamani et al. are particularly stringent in their application of criteria forconsistency with international environmental law principles (see section 3.1 in Rajamani et al.).
The fair share ranges assigned to individual countries by the CAT’s methods and Rajamani et al. arecomparable with differences relating to the method used to relate emissions levels to future warming
levels. These different methods are described in Hohne et al 20227. Both the Rajamani et al. and CAT
approaches serve to complement each other in developing a holistic fair share range for individual
countries.

Questions relating to the report by Climate Analytics, A 1.5°C compatible Switzerland

Question as received from Applicants

In its answers, Switzerland states that “like the IPCC in its reports, Climate Analytics makes
assumptions about societal and political developments in order to construct the climate scenarios.
However, in the case of the IPCC, these assumptions are very robust and provide a range of scenariosand multiple model runs to arrive at the value presented. The Climate Analytics analysis has severalshortcomings. In particular, the analysis does not provide a statistical range in its projections. Themodelling is almost linear with a starting point in 2020 and an end point in 2030. It is not clear how
Climate Analytics has accurately calculated a modelled trajectory for 1.5°C of warming”.
It is unclear from the phrasing of these comments to which modelling Switzerland is specificallyreferring, particularly because neither the A 1.5°C compatible Switzerland report nor theClimate Analytics 1.5°C national pathway explorer does contain a graph with a starting point in2020 and an endpoint in 2030. Such a pathway can, however, be found in the Climate Action
Tracker figure on Switzerland (last updated June 2022). For this reason we ask you to provide
two separate answers in relation to the following question. One as if the comment relates tomodel results on domestic emission reductions as depicted in Figure 1 of A 1.5°C compatible
Switzerland, and one as if the comment relates to the figure in the report of the Climate Action
Tracker on Switzerland.
Question 2: Could you provide a description of the scenario selection and methodology ofdefining a 1.5°C modelled trajectory for domestic emission reductions in Switzerland. In doingso, please also comment on the critique of Switzerland as quoted in the above and provide an
explanation of the difference between modelled domestic emission reduction and modelledfair share contributions.

Response on behalf of Climate Analytics and the CAT consortium

Re: A 1.5°C compatible Switzerland

The 1.5°C domestic pathways we develop are derived from scenarios assessed by the IPCC and included
in its databases; we downscale these scenarios to the national level using well established scientificmethods(describedindetailon
ourwebsite,e.g.
here:
http://1p5ndc-7

Höhne, N., Gidden, M. J., den Elzen, M., Hans, F., Fyson, C., Geiges, A., Jeffery, M. L., Gonzales-Zuñiga, S., Mooldijk,S., Hare, W., & Rogelj, J. (2021). Wave of net zero emission targets opens window to meeting the Paris Agreement.
Nature Climate Change, 11(10), 820–822. https://doi.org/10.1038/s41558-021-01142-2

4

pathways.climateanalytics.org/methodology/, and, for example, in Gidden et al. (2019)8). This meansthat the pathways we develop are based on the same socio-economic assumptions as the IPCC’sscenarios. We evaluate a full range of pathways from the IPCC’s database, although we exclude from
our analysis those scenarios that are not compatible with the Paris Agreement (for example, those thatovershoot 1.5°C to a high degree) and those that do not meet sustainability constraints defined by theIPCC.
We define the threshold for what is 1.5°C compatible for a given country by taking the median of therange across pathways; this is to ensure that the derived emissions still achieve the global temperature
goal when aggregated together across all assessed countries (if a country were to follow a pathwaythat falls in the upper end of the range, other countries would need to cut emissions faster than themedian in order to maintain 1.5°C compatibility). This means our results are based on a statistical range,
with the median of that range representing the least ambitious emissions reductions that could beconsidered 1.5°C compatible domestically.
The pathways we downscale are harmonised to historical data and have timesteps that are the same as
the original global pathways they are derived from (typically 5-yearly, out to 2100 in most cases).
The 1.5°C modelled domestic pathways we calculate show what emissions reductions are needed
domestically, within a country’s own borders, to be globally consistent with limiting warming to 1.5°C.
This is based on what is cost-effective from a global perspective (a core assumption underlying the IPCCassessed scenarios) and does not factor in what would be a fair contribution. We separately assess whata fair contribution would be, which for developed countries like Switzerland would need to be achieved
through a combination of domestic emissions reductions (following a 1.5°C compatible domesticpathway) and international support for developing countries (e.g. climate mitigation finance).
Re: Climate Action Tracker
The CAT rating of Switzerland is summarised in the following figure as shown on the CAT’s country
webpage.

8Gidden, M., Riahi, K., Smith, S. J., Fujimori, S., Luderer, G., Kriegler, E., van Vuuren, D. P., van den Berg, M., Feng, L.,
Klein, D., Calvin, K., Doelman, J. C., Frank, S., Fricko, O., Harmsen, M., Hasegawa, T., Havlik, P., Hilaire, J., Hoesly, R., …
Takahashi, K. (2019). Global emissions pathways under different socioeconomic scenarios for use in CMIP6: adataset of harmonized emissions trajectories through the end of the century. Geoscientific Model Development,12, 1443–1475.

5

The left part of the panel shows modelled domestic pathways for Switzerland that are consistent withdifferent levels of global warming. These are calculated by downscaling 250 IPCC-assessed global
pathways, which come from 8 different underlying models and cover the full range of Shared
Socioeconomic Pathways (SSPs) assessed by the IPCC. This means the CAT domestic pathways are basedon the same socio-economic assumptions as the IPCC’s global pathways.
The lines on the left panel show the median estimate of an ensemble of scenarios for a given
temperature category. We take the median as the threshold for each temperature category in order toensure that the derived emissions still achieve the global temperature level when aggregated together
across all assessed countries. The 1.5°C pathway in green uses the same method as the pathway shownin Figure 1 of the 1.5°C compatible Switzerland (note that the CAT pathways have been more recentlyupdated). Different from that report, the figure in the CAT only shows the pathways between the years
2020 and 2030. This is for reasons of comparability with the fair share results in the right panel which
are only modelled at 2030.
The linear appearance of the CAT domestic pathways should not be interpreted as meaning theunderlying modelling is linear; it is the result of the way we visualize the data and the truncation after2030. The underlying global models usually simulate in time-steps of 5 or 10 years. This means the CAT
pathways also have time-steps of 5 or 10 years (2020, 2025 and 2030), and we interpolate between data
points for visualisation purposes. The underlying models are not linear and continue up to at least 2060
(most go to 2100).

Prof Dr. Niklas Höhne, NewClimate InstituteBill Hare, CEO Climate Analytics(member of Climate Action Tracker consortium)(member of Climate Action Tracker consortium)

6