Introduction: Cities at the Forefront of Climate Change

Cities stand at the critical intersection of climate crisis and solutions. Housing over half the world’s population, urban areas generate three-quarters of global economic output while accounting for 67–72% of greenhouse gas emissions—a share projected to increase as 2.5 billion people join urban populations by 2050. This introductory chapter establishes the book’s foundational premise: that cities function simultaneously as hotspots of climate vulnerability and as laboratories for transformative innovation. The chapter traces the evolution of the Innovate4Cities initiative from the landmark 2018 Cities and Climate Change Science Conference in Edmonton, which catalyzed the creation of the Global Research and Action Agenda on Cities and Climate Change Science (GRAA). This transdisciplinary framework emphasizes knowledge co-generation, multi-level governance, and the localization of climate science to support context-appropriate urban decision-making. The chapter concludes by outlining the book’s three-part structure, which progresses from the GRAA’s foundational concepts through its unique enabling mechanisms to a comprehensive systems approach, ultimately providing a blueprint for sustained researcher-practitioner collaboration that accelerates equitable urban climate action aligned with the Paris Agreement’s 1.5 °C target.