the process of becoming more active about protecting the environment

The next ten years, he predicted, would see the greening of the US (= Americans starting to take more care of the environment). 他预测，在未来10年，美国人将越来越重视环保问题。

the process of making somewhere greener by planting grass, trees, and plants there

Concern about the ugly effects of industrialization has led to the greening of many of our cities. 人们对工业化带来的可怕后果的担忧已经促使我们的很多城市进行绿化。