Climate policies implemented by humans alter Earth's land, atmospheric, and oceanic conditions, ultimately modifying human societies through effects on agricultural yields, human health, water resources, and economic sectors. Earth System Models (ESMs) have provided invaluable insight into past and projected future system evolution but fall short when assessing policies requiring two-way interactions between societal dynamics and global environments. Here we use an integrated assessment model explicitly representing global economic markets, national governments, and socio-economic-technological changes, linked to an Earth System Model of intermediate complexity in an unprecedented manner. In a comprehensive scenario study including multiple Shared Socioeconomic Pathways (SSPs), we discover several important findings emerging only through integrated modeling. Under ambitious mitigation, for example, global warming remains largely below 2 °C throughout the 21st century under an SSP1-like pathway—an outcome unlikely in models without a realistic representation of international policy negotiations under fragmented global governance. The scenario space associated with the mitigation scenario also exhibits much faster rates of societal changes and shifts across the SSPs—indicating how future societal choices are not independent of climate policy. The comprehensive approach undertaken in our study offers unique insights to aid integrated sustainability research efforts aiming for a holistic description of human–Earth interaction.