The amount of atmospheric carbon has skyrocketed. And world leaders are balking at doing anything about it. What can one person do? Not much -- unless a lot of people take part.

That's why once a week until Earth Day 2012, we'll post one small thing you can do to lessen your carbon footprint. Indicate that you're on board by liking and sharing the small thing. The goal is to get enough people participating that one small thing will turn into be a very big deal. This week's thing is:

#4. Bike to Work.

It's Bike to Work Month. Hop on your bike saddle (or walk if that's a better option!) for your commute. Not sure how to get started? Need help? Visit the Sierra Club's bike resource page.