The earliest days of international expositions stressed concepts such as trade and progress, but in recent decades, they've become more and more focused on environmentalism: not just educating the public, but exploring what might be done to undo the damage and experimenting with new ideas and forms to reduce society's impact on the planet.

An unlikely place ushered in the first World's Fair focused on environmental issues: the small town of Spokane in the US state of Washington. It hosted the 1974 Expo on the Spokane River with the theme, "Celebrating Our Fresh New Environment". At the time, environmental awareness was just beginning and issues were mostly limited to local ones.

The state of our planet's water has been explored in many subsequent expositions. Okinawa's Expo in 1975 and Lisbon's Expo in 1998 focused on our oceans and New Orleans' 1984 Louisiana World Exposition looked at our rivers. The most recent world's fair, Expo in Zaragoza, Spain hosted The Water Tribune, a forum for experts and citizens to address worldwide issues related to water that resulted in The Zaragoza Charter, a document that summarized the conclusions of thousands of experts during the 2008 Expo's hundreds of lectures.