sustainablyadverb
uk/səˈsteɪ.nə.bli//səˈsteɪ.nə.bli/in a way that can continue over a period of time:
They were aiming for sustainably higher rates of pay for all their employees.
in a way that causes little or no damage to the environment and therefore able to continue for a long time:
The article is full of hints on how to live sustainably.