Some way out of this giant Ponzi scheme we're trapped in, where we need economic growth to pay for the technology that might, if we are lucky, fix the destruction caused by said economic growth before everything goes pear-shaped sometime around the turn of the century.
Cheap non-destructive energy. It doesn't have to be renewable, it just has to not mess up the ecosystem. Fusion would do.
Nanotechnology to recycle trash into new products and clean things up, like in "the engines of creation". Of couse, that's also the source of the "grey goo" apocalyptic vision, so let's be careful