From NPR:

With the season of Lent upon us, [Anglican] bishops in London and Liverpool have come up with a new kind of 40-day fast. Along with the aid agency Tearfund, the bishops have launched a carbon fast. Instead of giving up chocolate, how about giving up on plastic bags or incandescent light bulbs?

You can find out more about the fast here. Here's a taste, though:

Participants are asked to begin the Carbon Fast by removing one light bulb from a prominent place in the home and live without it for 40 days - as a constant visual reminder during Lent of the need to cut energy. On the final day of the Carbon Fast, people are encouraged to replace the missing bulb with an energy-saving bulb.