From Envirowiki

Environmental activism is social agitation for preservation or conservation of the environment, and/or against environmental destruction and waste. Environmental activism has a long and proud history.

Environmental activism can take many forms, including direct action, lobbying, and public awareness raising. Environmental direct action often has a strong affinity with non-violence.

Environmental activists often lay down their personal wellbeing (safety, community standing, wealth, etc) to protect the environment, knowing that in the end, even if they don't benefit directly from their efforts, others will.