Ouroboros is a family of proof-of-stake blockchain consensus protocols that can run both permissionless and permissioned blockchains.

Ouroboros 

Third, Ouroboros provide an elegant solution to total decentralization.

Pace University

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

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

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

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