fair-shares library

2026

A Python library that turns fair-share carbon budget allocation into transparent, reusable code

We operationalise 'fair shares' of remaining carbon budgets and emission pathways in an open-source Python library, developed with five collaborators. It computes budget and pathway allocations under equal per capita, convergence, and responsibility- and capability-adjusted approaches. Equity principles, allocation years and budget sources are all configurable. Allocation between countries is the central use case, but the allocation mathematics is general. The same machinery applies to any set of parties for which emissions, population and capability data can be supplied.

Building on the 'entry points' argument, we treat each equity assumption as a setting the user selects, not a default the code hides. The start year for historical emissions, for example, is a value judgement, and the documentation names it as one. Worked templates cover budget and pathway allocation from user-supplied inputs. Dedicated templates ingest IAMC-format scenario data, so allocations attach directly to integrated assessment model regions and scenario ensembles such as the AR6 database. Swapping a principle or a start year changes the allocation transparently, and the contested values remain visible in the output.

The library also reproduces published allocation studies as executable notebooks. These include the 2023 equity evaluation for the European Scientific Advisory Board on Climate Change, which can be updated as input data are revised. The quantitative analysis in several of our climate equity papers runs on this library, so those results share one auditable code base.

@software{pelz_fairshares_2025,
	title = {fair-shares: {Python} package for calculating fair shares of remaining carbon budgets and emission pathways},
	author = {Pelz, Setu and Holz, Ceecee and Lamboll, Robin and Weber, Konstantin and Lewis, Jared and Nicholls, Zebedee},
	year = {2025},
	version = {0.2.0},
	license = {BSD-3-Clause},
	url = {https://github.com/setupelz/fair-shares},
}