For many young people, environmentalism has become almost a religion in their daily lives.

religion 的基本意思是"宗教"，指有特定信仰体系、仪式和道德准则的信仰系统。在这里用作比喻意义，表示"像宗教般虔诚的信念或追求"，强调环保主义在年轻人生活中占据着类似宗教信仰般的重要地位。