Sustainability Debt: A Metaphor to Support Sustainability Design Decisions

Sustainability, the capacity to endure, is fundamental for the societies on our planet. Despite its increasing recognition in software engineering, it remains difficult to assess the delayed systemic effects of decisions taken in requirements engineering and systems design. To support this difficult task, this paper introduces the concept of sustainability debt. The metaphor helps in the discovery, documentation, and communication of sustainability issues in requirements engineering. We build on the existing metaphor of technical debt and extend it to four other dimensions of sustainability to help think about sustainabilityaware software systems engineering. We highlight the meaning of debt in each dimension and the relationships between those dimensions. Finally, we discuss the use of the metaphor and explore how it can help us to design sustainability-aware software intensive systems.