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

2009
Needed: Leadership From Architects and Designers
Julia Levitt encourages architects to lead cities toward greater sustainability at the policy making level. She says, "We urgently need people to re-imagine their cities in very directly political ways, and no one else is as prepared for that job as the talented few who've been trained to understand form and space and place." This article stimulated some good conversation in the comments...

2008
Unclogging the Water and Sanitation Crisis
Access to clean drinking water is a concern world-wide – but it is not the sole responsibility of government to provide it. The Next 4 Billion report concluded that there is a clear willingness to pay for clean water in the BoP. However, even if there is a willingness to pay, access to such services is not widespread, especially in rural areas. Ashoka’s Changemakers has partnered with The Global Water Challenge to launch a collaborative competition to discuss and discover new solutions...

2005
Ghost Nets and Remote Sensing
Ghost nets -- nets lost or abandoned by fishing fleets -- are, along with other ocean trash, becoming a major ecological problem. Remote sensing, developed by NOAA scientists, may help crews find, track, and (hopefully eventually) clean up ghost nets...

Other recent "look backs":
April 30
May 3
May 4