The idea of the Global Commons has for centuries driven such wide range of domains as international law, colonial expeditions, ideas about universal democracy, and even hopes for a shared and healthy environmental destiny. Until now, key Global Commons - the 'public good' - have served as waste receptacles for the 'private bad'. Common afflictions from energy to economics have brought humankind to the brink of planetary systems failure. And yet, only in seizing on the very uncommon promise that the idea of the Global Commons harbours lies the prospect for confronting and overcoming common threats. For this, several common challenges are to be overcome. Among these are common and comforting myths about the nature and state of the biosphere, leading to the erroneous idea that climate neutrality offers a safe policy haven, or that trading in emissions lowers climate risk, and does more than extend business-as-usual. A broader and deeper, even unflinching understanding of both economy and science is crucial – and a new appreciation of planetary dimensionality, going beyond the conventional dimensions of space and time, and understanding key Global Commons themselves as planetary dimensions that are inseparably interdependent in the fundamental fluidity of terrestrial, oceanic and atmospheric interactions. Herein lies more than ample scope for geodesigners to find a common mission.