The gap between what is known about climate change and the action taken to prevent it has instigated debates around how to reconfigure global environmental assessment organizations to better inform and foster transformative change. One recurring request involves the need for a broader and better inclusion of social scientific knowledge. However, despite such intentions, the inclusion of social scientific research remains limited. How can this be explained? Through a detailed analysis of the IPCC special report on limiting global warming to 1.5 degrees, this article reveals how the institutional conditions of global environmental assessments condition and shape what knowledge is included in these assessments, as well as how this knowledge is represented. It discusses how and why the understanding of social processes and structures remains underdeveloped, despite such knowledge being critical for transformative change. To integrate such knowledge into environmental assessments would require substantial changes to the current epistemic infrastructure used by global environmental assessments. It is therefore time to think beyond global environmental assessments and consider complementary institutional science–policy relations through which social scientific research can assist policy actions to promote deep transformative change.