Looking back one, two and five years ago today (give or take!) on Worldchanging:

2009
Defusing The Population Bomb
Adam Stein reflects on a study that suggests family planning is one of the lowest-cost ways to reduce CO2...

2008
Reader Report: The Carbon Footprint of Research at Caltech
Asa S. Hopkins, a graduate student studying physics at Caltech, shares his ideas about how to make this major research institution more sustainable...

2005
Green City China
Jamais Cascio reports on Arup's plans to design a "eco-city" expansion to Shanghai...

Other recent "look backs":
September 8
September 9
September 10