Not because things are going well on the environmental front, but to celebrate movements and people who are committed to environmental issues.
Remember this march of some 300,000 people in Montréal in 2012 - a far more clement spring, and in the midst of the student movement, becoming much more than a student movement
https://www.youtube.com/watch?v=70YO8Uyb6JE
We also pause to remember the many defenders of the earth who have been murdered for their activism.