it's notot sustainablele, andy dedefinition, a a system that it sustaiainable will c collapsoe day or a another, and,d, actua, thisis day is pretetty close . raphaelle: sometimes it's rdrd fit toto stahopefuful. the more we know aboutut the fututure, the lessss easy it io stay h hopeful, but t i hope o things. the e firsthing g that i hope s that, ifif we cannotot stop completely climate c change, e can limit t it amuch a as possible.. another thing that i i hope is that i hopope for more s solidy around the w world. reporter: one of theain n goal the climate camp inrance is to raiseororale amg yoyoung activivists, to giveve them the sense thatat together ththey're ststrong, and ththey have the r toto make a difffferen. host: making a difference is a key focus of our "global ideas" series, too. this week we look at renewable energy sources. in future, many manufacturing processes will no longer rely on wind and solar power. our reporter, wolfgang bernert, travelled to arandas in mexico and discovered more about a start-up that's helping other companies harness solar thermal energy. re