Nitrogen Cycling in Earth System Models: From Constraining Carbon Budgets to Projecting Pollution for Planetary Stewardship

Abstract Terrestrial nitrogen cycling plays a vital role in the Earth system, influencing climate change and a myriad of dimensions of human well‐being. Earth system models (ESMs) are used to project climate change and increasingly include a representation of terrestrial nitrogen cycling. In this review, we highlight how ESMs primarily focus on nitrogen limitation of primary productivity and carbon sequestration but generally neglect nitrogen losses from the terrestrial biosphere to the atmosphere and hydrosphere which are strongly influenced by human activities. These include key flows of nitrogen such as nitrogen gas emissions from soils and wildfires as well as its transport through the land to ocean aquatic continuum. ESMs with fully interactive nitrogen cycling could both improve climate change projections and be used to project nitrogen pollution and its impacts to inform planetary stewardship over the 21st century.