Abstract:Either meeting the UNFCCC Paris agreement to limit global average warming below the 2-1.5 • C threshold, or going beyond it entails huge challenges in terms of institutional innovation and transformation. This research describes a participatory integrated assessment process aimed at exploring the options, opportunities, necessary capacities and implications for institutional co-operation and innovation in the Iberian Peninsula under High-End Climate Change (HECC). Using in-depth interviews and a novel participatory research approach, different scenario narratives and pathways about the future of Iberia have been identified using Shared Socio-economic Pathways (SSPs). Special attention is given to the knowledge and policy options needed to implement cross-border organizational changes and co-operation mechanisms that would support the Integrated Climate Governance of the Tagus and Guadiana river basins. We show that a wealth of institutional innovation pathways and specific options and solutions exist not only to reduce GHG emissions (mitigation) and the negative impacts of climate change (adaptation), but, above all, to generate new forms of social-ecological system interactions aligned with sustainability (transformation). In particular, and depending on which scenario contexts unfold in the future in Iberia, different kinds of institutional and governance capacities and clusters of solutions may be needed in order to achieve transformation.