Do Parties to the Paris Agreement comply with their commitments under that Agreement, contained in particular in Arts. 4.3 and 4.11 and Decision 4/CMA.1, if their new or updated nationally determined contribution (“NDC”) does not represent a progression beyond the previous NDC, in so far as it effectively lowers an existing economy-wide absolute emissions reduction target, due to methodological changes in the calculation of their emission inventories?
Does the Paris Agreement create a legal obligation on its Parties to ensure that when they submit or update an NDC, the new absolute emission reduction target does, at a minimum, not fall behind the previous goal?
The Paris Agreement is an international, legally binding treaty regarding climate change. Adopted by 196 Parties, the treaty aims to strengthen the global response to the threat of climate change, including by limiting global warming to well below 2°C above pre-industrial levels. The Paris Agreement mandates that all Parties outline their planned climate actions in an NDCand that they take domestic mitigation measures to achieve the stated objectives. Art. 4 of the Paris Agreement requires Parties to prepare and communicate ‘successive’ NDCs every five years, representing ‘progression beyond the Party’s then current’ NDC and Parties’ highest possible ambition.
In order to assess the scope of the commitments made by Parties to the Paris Agreement and whether or not there has been a breach of such commitments, the Vienna Convention on the Law of Treaties (“VCLT”), which governs treaty interpretation, will be relevant. The VCLT provides that treaty terms must be interpreted in good faith and in accordance with their ordinary meaning. Under the VCLT framework, the context of relevant terms (including the full treaty and its preamble) and the treaty’s object and purpose will inform the “ordinary meaning.” An agreement’s object and purpose may be ascertained by reference to the entire treaty, including the preamble and any provisions detailing specific objectives. Additionally, Parties’ subsequent agreements or practice regarding a treaty’s interpretation or functionality may also inform the “ordinary meaning.”
Other sources may further inform this analysis. For example, preparatory works and the circumstances of a treaty’s adoption may confirm the “ordinary meaning” of specific terms. Lastly, when a treaty has more than one official language, there is a general presumption that the treaty terms are consistent across all versions.
Textual interpretation of the ‘progression’ requirement
None of the provisions of the Paris Agreement explicitly prohibits the submission of an NDC which represents a lower contribution than the then current NDC. Consequently, whether or not there has been a breach by a Party of its commitments under the treaty by downgrading its NDC, will be a matter of interpretation.
As set out below, Arts. 4.3 and 4.11 have widely been interpreted as requiring Parties to employ their best efforts to set and achieve progressively more ambitious mitigation targets. This implies that a subsequent NDC should reflect a greater reduction in emissions than the preceding NDC. This conclusion is supported by Art 4.11 which provides that if a Party wishes to update its existing NDC, it may do so only in the direction of greater ambition.
In our view, on the basis of an interpretation of the relevant provisions of the treaty in accordance with the VCLT framework if a Party downgrades its NDC commitments, it likely violates its obligations under the Paris Agreement:
- Article 4.3 of the Paris Agreement presumes progression in emission mitigation efforts over time, stating that each Party’s successive NDC “will represent a progression beyond the Party’s then current nationally determined contribution and reflect its highest possible ambition, reflecting its common but differentiated responsibilities and respective capabilities, in the light of different national circumstances.” An ordinary reading of Art. 4.3 indicates that progression is a condition that Parties “will” fulfill in NDC submissions, imposing an obligation to increase ambition over time. Moreover, each NDC is expected to reflect a Party’s “highest possible ambition,” which is akin to a standard of conduct that Parties are expected to meet. This standard strongly implies that Parties should craft domestic policies that reduce emissions to the greatest extent possible given their respective capabilities. Consequently, a Party that downgrades its NDC submission likely violates Art. 4.3 by decreasing efforts to reduce emissions, absent a reduction in state capacity to meet higher targets. On this latter point, at least one commentator has theorized that economic or political changes are likely not valid “national circumstances” under Art. 4.3 to justify lowering an NDC.
- Article 4.11 of the Paris Agreement permits amendments to current NDCs, but further presumes progression in stating that a Party may “adjust its existing nationally determined contribution with a view to enhancing its level of ambition.” On an ordinary reading, “enhance” means “to raise the level of” or “increase,” strongly suggesting that any adjustments to a current NDC must be in an upward direction.
Treaty context, object and purpose
Numerous other provisions in the text of the Paris Agreement reinforce the conclusion that a downgrade in a Party’s NDC would contravene such Party’s commitments under the treaty, and the object and purpose of the Paris Agreement itself:
- The Preamble of the Paris Agreement recognizes “the need for an effective and progressive response to the urgent threat of climate change,” establishing that progression is central to the Paris Agreement’s stated purpose of combatting a time-sensitive danger.
- Article 2 reiterates the “urgency” required from Parties in reaching the Paris Agreement’s long-term goals.
- Article 3 states that “the efforts of all parties will represent a progression over time” and provides that a Party’s efforts under the treaty must be “ambitious.”
- Article 4.1 further states that the goals of Art. 2 require that Parties “aim to reach global peaking of greenhouse gas emissions as soon as possible.”
- Article 4.2 provides in its second sentence, that the Parties “shall pursue domestic mitigation measures, with the aim of achieving the objectives of such contribution.”
- Article 4.4 provides that developed countries “should continue taking the lead by undertaking economy-wide absolute emission reduction targets,” while developing countries should “continue enhancing their mitigation efforts, and are encouraged to move over time towards economy-wide emission reduction or limitation targets in the light of different national circumstances.”
- Article 4.13 provides that “[i]n accounting for anthropogenic emissions and removals corresponding to their nationally determined contributions, Parties shall promote environmental integrity, transparency, accuracy, completeness, comparability and consistency, and ensure the avoidance of double counting[.]” The inclusion of “consistency” as a fundamental accounting principle suggests that methodological changes which have the effect of generating inconsistency across NDCs potentially contravene the Paris Agreement, particularly when they effect a downgrade of NDCs.
- Arts. 4.3 and 4.11 read in the broader context of the Paris Agreement, as described above, suggest that achieving target national contribution levels is a time sensitive matter. Permitting a Party to downgrade its NDC, including through methodological changes, would thus undermine the fundamental logic of the Paris Agreement as such an action would escalate, rather than mitigate, the dire threat of climate change.
A number of decisions and standards developed during the negotiations leading up to the ratification of the Paris Agreement provide further support for the principle of progression and weigh against downgrades of a Party’s NDC:
- Decision 1/CP.20 of 2014 (“the Lima Decision”) first expressed the principle of progression, replacing the notion of “no-backsliding” (from Kyoto Protocol commitments) that had been expressed during prior negotiations. The “no-backsliding” notion was subsequently translated into the Paris Agreement’s forward-looking progression principle, which has been interpreted as a standard of care establishing that a Party’s current commitments form a floor beyond which future commitments may not regress.
- The Geneva NegotiatingText (which formed the basis for Paris Agreement negotiations) discussed both progressive and regressive NDC revisions:
Article 4.11 of the Paris Agreement is based on paragraph 180 of the Geneva Negotiating Text, which stated that updates to existing NDCs must take an “upward direction.” Although “upward” was not incorporated into the final version of the Paris Agreement’s Art. 4.11, commentators believe that this is not an indication that the drafters of the current text intended to move away from the expectation of upward adjustment. 
Paragraph 181 of the Negotiating Text also contemplated various options to allow for downgrading, including in cases where developing countries suffer from natural events or are deprived of capacity for mitigation efforts. These options were ultimately not included in the Paris Agreement. It is possible that excluding these provisions could be interpreted as a flexibility toward downgrading. However, in our view the better opinion as expressed by commentators is that because downgrading is against the spirit of the Paris Agreement, these provisions were excluded to prevent Parties from contemplating non-progression as an acceptable policy.
Subsequent agreements and/or practice regarding the interpretation of the Paris Agreement
Decision 4/CMA.1, a subsequent decision that clarified Parties’ obligations under the Paris Agreement offers guidance on the type of information the Parties should provide in their NDCs to enhance the clarity, transparency, and understanding of ambitions, and sets out a number of accounting requirements that Parties must follow in preparing and reporting their NDCs. Several aspects of this decision further reinforce the principle of progression and suggest that a downgrade of a Party’s NDC, even if accomplished implicitly via methodological changes, is not permissible under the Paris Agreement:
Parties are required under this decision to “maintain consistency in scope and coverage, definitions, data sources, metrics, assumptions and methodological approaches.” The principle of consistency is reinforced in several other places in the document and other decisions by the Parties. This suggests that a sudden departure from a previously established methodology for calculating emissions inventories may fall foul of the Parties’ intentions and interpretation of the Paris Agreement, particularly when it results in a downgrade of a Party’s NDC.
Parties should “transparently report any methodological changes and technical updates made duringthe implementation of their nationally determined contribution.” Accordingly, if a Party wishes to change its methodology for calculating NDCs, and thereby effectively lower its NDC, it would likely have to provide an in-depth and transparent explanation about the motivations behind the change, clarifying why the previous methodology, or another methodology that would not result in a lowered NDC is not acceptable and how the new methodology complies with this and other requirements of Decision 4/CMA.1.
Non-English language versions
The English version of Art. 4.11 of the Paris Agreement states that a Party may “adjust its existing nationally determined contribution with a view to enhancing its level of ambition.”Although the English phrasing “with a view to” suggests a softer commitment to the principle of progression, the French and Spanish versions go further, providing that a Party may modify its NDC “in order to” or “for the purpose of” raising its level of ambition (i.e., “afin d’en relever le niveau d’ambition” in French and “con miras a aumentar su nivel de ambición”in Spanish). Moreover, unlike the English text of the Paris Agreement’s Preamble, which references a “pursuit” of the objective of the treaty, the preamble to the French version declares the Parties “eager to achieve the objective.” Given the aforementioned presumption of consistency, these formulations provide further support for the principle of progression such that Parties may not lower their NDCs and remain in compliance with the Paris Agreement.
 What is the Paris Agreement?, UNFCCC (last accessed May 27, 2022) (available here).
 Paris Agreement (December 12, 2015) (available here).
 The Paris Agreement and NDCs, UNFCCC (last accessed May 27, 2022) (available here).
 Unless the treaty indicates otherwise, terms’ ordinary meaning governs. VCLT Art. 31(1).
 Ibid. Art. 31(2). See also Richard K. Gardiner, Treaty Interpretation (Oxford University Press 2008) page 192 (further confirming that treaty terms are often ascertained by reference to the entire text).
 VCLT Art. 31(2)(b).
 Ibid. Art. 32.
 Ibid. Art. 33(3).
 See generally, Lavanya Rajamani & Jutta Brunnee, The Legality of Downgrading Nationally Determined Contributions under the Paris Agreement: Lessons from the US Disengagement, Journal of Environmental Law (2017) (explaining that the Paris Agreement urges Parties to set ambitious target levels, while adopting measures to achieve such targets).
 Paris Agreement Art. 4.3.
 Interpretation of Article 4.11 Paris Agreement, Lawyers Responding to Climate Change (May 15, 2017) (available here) (explaining that the Paris Agreement is not binding).
 On the Paris Agreement’s Imminent Entry into Force (Part II of II), Christina Voigt (October 12, 2016) (available here) (explaining that Parties are expected to adopt mitigation measures to achieve NDCs).
 Ibid. (“Each successive NDC has to progress beyond previous undertakings. A Party’s changing circumstances (e.g. a financial, political or economic crisis) cannot lead to a decrease in what can be considered its ‘highest possible ambition’ compared to the level contained in the previous NDC.”); see also The Paris Agreement and NDCs, UNFCCC (last accessed May 27, 2022) (available here).
 Paris Agreement Art. 4.11.
 See Interpretation of Article 4.11 Paris Agreement, Lawyers Responding to Climate Change (May 15, 2017) (available here) (explaining that the Paris Agreement strongly suggests progression in NDCs).
 Paris Agreement Preamble.
 Ibid. Art. 2.
 Ibid. Art. 3.
 Ibid. See also Interpretation of Article 4.11 Paris Agreement, Lawyers Responding to Climate Change (May 15, 2017) (available here) (further emphasizing that the Paris Agreement’s plain language suggests a progression requirement).
 Paris Agreement Art. 4.1.
 Ibid. Art. 4.2. See also Benoit Mayer, International Law Obligations Arising in Relation to Nationally Determined Contributions, page 7 (available here) (explaining that this requirement is substantive, rather than procedural).
 Paris Agreement Art. 4.4. See also ECBI, Paris Agreement Pocket Guide, page 7 (available here) (explaining that lesser developed countries may not need to reach mitigation results as quickly as more developed countries).
 Paris AgreementArt. 4.13.
 Ibid. Arts. 4.2 and 4.11.
 Lavanya Rajamani & Jutta Brunnee, The Legality of Downgrading Nationally Determined Contributions under the Paris Agreement: Lessons from the US Disengagement, Journal of Environmental Law, page 544 (2017) (citing FCCC, Decision 1/CP.20, ‘Lima Call for Climate Action’ (February 2, 2015) FCCC/CP/2014/10/Add1, 2, para 10) (explaining the historical development of the Paris Agreement’s progression requirement).
 See Interpretation of Article 4.11 Paris Agreement, Lawyers Responding to Climate Change (May 15, 2017) (available here) (explaining that the negotiations leading up to the Paris Agreement strongly suggest an intent to impose a substantive progression requirement on Parties).
 Decision 4/CMA.1 (March 19, 2019) (available here) (hereinafter Decision 4/CMA.1), Annex I paragraphs 6 and 7 (requiring that a Party disclose how it considers that its nationally determined contribution is fair and ambitious in the light of its national circumstances, and how its NDC contributes towards achieving the objective of the Convention as set out in its Art. 2, including the temperature targets set out at Paris Agreement Art. 2(1)(a)).
 Ibid. Annex II paragraph 2(a).
 See e.g., ibid. paragraph 11 (recalling the provisions of Paris Agreement Art. 4.13 noting that “Parties shall promote…consistency” in accounting); paragraph 12 (recalling Decision 1/CP.21, paragraph 31, which “ensures that… Parties ensure methodological consistency, including on baselines, between the communication and implementation of nationally determined contributions”); Annex II paragraph 2 (the heading of which reads “Ensuring methodological consistency, including on baselines, between the communication and implementation of nationally determined contributions”); and Annex 11 paragraph 2(d)(ii) (“Improvements in accuracy that maintain methodological consistency[.]”).
 Ibid. paragraph 2(e) (emphasis added). Parties must also explain why any categories of anthropogenic emissions or removals are excluded from an NDC accounting. See ibid. at paragraphs 3 and 4.
 Paris Agreement Art. 4.11.
 Ibid. (French and Spanish versions). See also Lavanya Rajamani & Jutta Brunnee, The Legality of Downgrading Nationally Determined Contributions under the Paris Agreement: Lessons from the US Disengagement, Journal of Environmental Law, page 548 (2017) (highlighting that foreign language editions of the Paris Agreement suggest a strong intent for progression).
 Ibid. at page 548.