Also while they are blocking traffic all those vehicles are sitting there idling, spewing the very greenhouse gases they are protesting against. If the goal is to reduce GHG emissions, forcing people to burn extra gas while they sit in a traffic jam that the activists created is achieving the exact opposite effect. And it angers a lot of people who are then less likely to support their agenda.

But they do get to pat themselves on the back and give themselves participation awards for "doing something" about a crisis that continues to go on exactly as it was the day before.