Global warming has caused green efforts to be fashionable. And here’s Zipcar, a leading car-sharing service announcing $21 million in their 6th round of financing. The round was led by Meritech Capital partners with $20 million investment joined by Pinnacle Ventures LLC putting up $1 million.

The funds will be used for both capital needs and growth of product offerings, as well as stabilize their assets and liabilities. ZipCar has 500,000 members and 8,000 vehicles in urban areas and colleges across United States, Canada and United Kingdom.

Zipcar believes that renting out a car instead of buying your own will decrease pollution–fewer cars, fewer pollution. If 10% of the population adopts their method, it means saving billions of gallons of gas and oil every year.

Another rent-a-car service, RelayRides, had some announcements yesterday – they’re funded by Google Ventures. “Your car, which is usually a burden, is an asset and something that can actually generate money,” said RelayRides Chief Executive Officer Shelby Clark. “Significant money is being put in people’s pockets.”

The significance of this all is how technology and improved communicatins can actually enable a system to work more effeciently.  In the case of ZipCar, that system is a rental service providing cars to people, so they can be used only when needed.  Without a large infrastructure to support this, an automated system and concentrated energy efforts, ZipCar, RelayRides and other systems wouldn’t work at all.  It’s certainly a glimmer of hope for those that look at our wasteful behavior and seek change through some of that inherent behavior itself.