Looking back one, two and five years ago today on Worldchanging:

2009
David Bollier On The Principles Of The Commons
Ethan Zuckermann reviews David Bollier's book Viral Spiral, which is a history of the idea of the commons, spreading from the free software movement to projects like Creative Commons, into international projects like the open educational resources movement, Science Commons and investigations of open business models...

2008
Guest Editorial: Water Trading in China: A Step Toward Sustainability
Yingling Liu reports that a new regulation from China's water authority may hold the key to achieving water sustainability in this thirsty country....

2005
Vital Signs 2005: The Looming China Syndrome
Joel Makower looks at Vital Signs 2005, the latest annual pulse-taking from the venerable Worldwatch Institute, which shows that those 'what-if' environmental impacts scenarios of a billion-plus Chinese aspiring to Americans levels of consumption are no longer hypothetical...

Other recent "look backs":
May 10
May 11
May 12