What is needed is sustainable activism. It is going to take at least our lifetimes to avert the global crises we face and find sustainable ways of living on the earth and with each other. To be involved and stay involved, always moving against the tide of the wider society, requires ways of continually replenishing our inner resources. Personal and spiritual growth, clarification of ethics and values as well as big picture perspective are important here. The causes of burnout are well-understood and preventable with personal and organisational contributing factors.
Prevention includes paying attention to support structures.
This appears to be given a low priority by environmental organisations driven by a crisis mentality. It is akin to strip-mining your own resources. Reflection and action learning techniques can be used so that critical learning from experience is not lost. In organisations where turnover is high, far too many wheels are reinvented. It is important to reflect on the assumptions that govern strategies, and to evaluate and adapt what we do for continuous improvement.