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Approach Catalog

All allocation approaches at a glance.

The Allocation Year Parameter

When allocation_year (budget) or first_allocation_year (pathway) is set in the past, past emissions are subtracted from the budget before allocation. Countries have different remaining allocations depending on historical emissions.

The choice of start date is normatively significant: 1850 captures the full industrial era, 1950 tracks post-war growth, and 1990 corresponds to the IPCC First Assessment Report — widely treated in the equity literature as the "excusable ignorance" threshold, beyond which responsibility for emissions harm is difficult to deny [Baer 2013; Pelz 2025b].

See Allocation Approaches for configuration details.

Budget Approaches

Allocate a cumulative emissions budget at a single point in time.

Approach Use Case
equal-per-capita-budget Population-proportional targets
per-capita-adjusted-budget Additional weighting by emissions history (historical responsibility) and GDP (ability to pay)
per-capita-adjusted-gini-budget Accounts for within-country inequality

Pathway Approaches

Allocate emissions over multiple years, producing annual shares.

Equal Per Capita Family

These approaches implement Equal Cumulative Per Capita (ECPC) allocation when an allocation_year in the past is used, ensuring historical emissions count against each country's share.

Approach Use Case
equal-per-capita Year-by-year population shares
per-capita-adjusted Additional weighting by emissions history (historical responsibility) and GDP (ability to pay)
per-capita-adjusted-gini Accounts for within-country inequality

Convergence Family

Gradual transition from current emissions to fair share target.

Approach Use Case
per-capita-convergence Comparison baseline (not a fair share approach) — convergence from current emission levels embeds implicit grandfathering during the transition period [Kartha 2018]
cumulative-per-capita-convergence Budget-preserving transitions
cumulative-per-capita-convergence-adjusted Additional weighting by emissions history and GDP
cumulative-per-capita-convergence-gini-adjusted Accounts for within-country inequality

Choosing an Approach

Question Answer
Single target or year-by-year? Budget vs Pathway
Account for history (historical responsibility)? Set early allocation_year
Account for capability (ability to pay)? Use -adjusted variants
Account for within-country inequality? Use -gini variants

See Principle to Code for detailed configuration.

Entry Points Framework

Approach selection is one of five structured decision stages in fair share quantification [Pelz 2025b]. Before choosing an approach, make explicit decisions about (1) foundational principles, (2) allocation quantity, and (3) which indicators will operationalize your approach — these upstream choices constrain which approaches are normatively coherent. See From Principle to Code for the full framework.

Registry Reference

All approaches are registered in src/fair_shares/library/allocations/manager.py.

Python
from fair_shares.library.allocations.manager import get_allocation_functions

approaches = get_allocation_functions()
print(list(approaches.keys()))

Adding Approaches

See the Developer Guide.