There are three main principles in Cardano's sustainability. The first principle is an integrated treasury system within Cardano. 

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Through Cardano's proof of stake consensus, it is less power intensive and more environmentally friendly.

Sustainability of Cardano 

Hoskinson, Charles. (2017). Why Cardano. https://why.cardano.org/

Second, a formal process is deployed to propose Cardano Improvement Proposals through a system coordinated by CSL.

Third, Ouroboros provide an elegant solution to total decentralization.