Emergent constraints on climate sensitivities

Emergent constraints (ECs) relate observables of the climate system to equivalent quantities simulated from Earth system models that are related to properties of the future climate. The uncertainties in projections of these properties may be reduced by constraining the modeled quantities to observables. The article examines how such relationships emerge from Earth system models, simple theories for how ECs can be derived from temporal variability in the climate system, and how ECs might be misinterpreted. A wide range of ECs discovered so far are presented as well as a framework for quantifying multiple sources of uncertainty in ECs. An outlook for reducing these uncertainties to quantify global environmental change is also given.