To date, we lack an understanding of how to manage the global transition towards carbon neutrality in a coordinated way. Building on transition management and portfolio management, we examined how actors from ministries, agencies, cities, firms and NGOs across three countries organized their projects to address climate change. Our empirical work based on 30 interviews revealed six organizational challenges: (1) global ambition; (2) national complexity; (3) coordination across project portfolios; (4) governance of project portfolios; (5) continuously changing context; and (6) ownership. Underlining these challenges is the need of connections between climate projects. We propose a novel way of conceiving project portfolio management as an approach to make these connections that coordinates across multiple levels of analysis and loosely connected organizational settings. Going forward, we call for more research on cross-organizational project portfolio management to lead societal transitions.