POLICYFORUM S

cience assessments indicate that human activities are moving several of Earth’s sub-systems outside the range of natural variability typical for the previous 500,000 years ( 1, 2). Human societies must now change course and steer away from criti-cal tipping points in the Earth system that might lead to rapid and irreversible change ( 3). This requires fundamental reorientation and restructuring of national and international institutions toward more effective Earth sys-tem governance and planetary stewardship. We propose building blocks of such a new institutional framework, based on a compre-hensive assessment conducted in 2011 by the Earth System Governance Project, a 10-year social science–based research program under the auspices of the International Human Dimensions Programme on Global Environ-mental Change (IHDP) ( 4, 5). The assess