Subnational Carbon Budget Assessments

This prompt presents an opportunity to apply equity assessments to U.S. States as metric for their fair climate pledges.
PROMPT WS2: Subnational actors, including alliances of state governments, have risen across the world to both implement climate actions and reveal additional potential to enhance national pledges. Multiple states in the US stepped up and declared 'We Are Still In'. Develop an initial simplistic approach to determine how much each US State should mitigate to do its share of the Paris Agreement.
Prompt Host: Yann Robiou Du Pont (IDDRI) Discord [for communication] CoMakery [for task management]

Political rationale

National governments agreed on the ambitious Paris Agreement as a framework to drive global climate action. Yet, the aggregation of the Nationally Determined Contributions (NDCs) remain insufficient to achieve its temperature thresholds, and even the implementation of these commitments is not on track. Worryingly, the federal government of the US has announced its intent to withdraw from the Paris Agreement.
Subnational actors, including alliances of state governments, have risen across the world to both implement climate actions and reveal additional potential to enhance national pledges. Multiple states in the US stepped up and declared 'We Are Still In'. States around the world are seeking to do their share of the Paris Agreement and many have announced climate pledges and emissions strategies. Their contributions are welcomed by the UNFCCC and increasingly acknowledged in stocktaking exercises on global action despite their diverse methodology, scopes and ambitions. Following calls to align Sub-national Climate Actions for the Post-Paris Regime, this study addresses the question of determining adequate state-level mitigation under the Paris Agreement:

How much should each state mitigate emissions to do its share of the Paris Agreement or of its country's NDC?

The question of how much mitigation each state should deliver is currently not answered by the scientific literature or think-tanks' action trackers.

Scientific rationale

While subnational governments are crucial actors of the climate transition, they are not Parties of the UNFCCC negotiations and their actions are not sufficiently reflected in the scientific literature taking stock of global progress. A recent article from the University of Yale called for coherent quantitative roadmap to assess of subnational action. The work suggested here would contribute to this body of knowledge by providing emissions targets coherent across different countries' states and consistent with the state-of-the-art literature on national emissions targets towards meeting the Paris Agreement. National fair shares to the Paris Agreement and current NDCs can now be downscaled to the state level. Under the Paris Agreement, the equity principle underlying national responsibilities to mitigate emissions is guided by the "Common but Differentiated Responsibilities and Respective Capabilities (CBDR–RC)" principle. Scientific literature quantifies the distribution of emissions allocation (and thus mitigation effort) to each country on the basis of their population, historical responsibility and financial capacity. The subnational distribution of efforts can be articulated around various combination of these principles, in light of governance structure and the degree of redistribution mechanisms across states.
The state-level emissions pathways derived in this work could be embedded in local discussions around just transitions with civil societies and non-state actors.

Practical use / relevance

By committing to do their share of their country's NDC, states contribute to multi-level commitments can help lock-in existing commitments by mitigating the effect of federal backtracking. Going further, states can help ratcheting-up ambition by adopting and implementing ambitious medium- and long-term targets consistent with the Paris Agreement.
The strategies to achieve such targets can be discussed businesses and non-state actors internally and aligned with other states even internationally. The adoption of coherent mitigation targets facilitates the setup of emissions markets by avoiding the leakage of climate credits towards less ambitious jurisdictions.


(data here refers to annual time series)
  1. 1.
    Retrieve online the best available (official when possible) state-level and national data with
    • Historical emissions (GHG, excluding land-use emissions), population and GDP
    • Projections of population and GDP as far into the future as possible
  2. 2.
    [scientific necessity but may be overlooked for the Collabathon] Check consistency, proceed to harmonisation if necessary between state-level and national total. Highlight and plot discrepancies (sum of subnationals vs. national total, historical data and projections...).
  3. 3.
    [optional] Extend projections until 2100 using national level growth rates from last data available
  4. 4.
    Multiply dynamically (at each time-step) the national allocation for the US from the Equal Per Capita trajectory ( ) or from the hybrid allocation ( ) by the state-share of the national population. Tadaaa you have equal per capita sharing across states of the national allocation.
Detailed methods if you are really desperate (my PhD defence):


You can find national data projections here: National historical data is here: Credit to: Gütschow, J.; Jeffery, L.; Gieseke, R.; Gebel, R.; Stevens, D.; Krapp, M.; Rocha, M. (2016): The PRIMAP-hist national historical emissions time series, Earth Syst. Sci. Data, 8, 571-603, and Gütschow, J.; Jeffery, L.; Gieseke, R. (2019): The PRIMAP-hist national historical emissions time series (1850-2016). v2.0. GFZ Data Services. National 'equitable' allocations are on the website:
The outcome data cannot be cited or used for policy/scientific advise. It will not be reliable data, only indicative of the type of product that we can deliver with further work.