'Net zero emissions' objective in the Paris Agreement: Meaning and implications

The Paris Agreement includes the objective of achieving 'net zero emissions' of greenhouse gases in the second half of the century. The exact wording, however, raises several scientific questions. How to distinguish between anthropogenic emissions and removals subject to the agreement, and the natural flows of these same gases? Which gases should be included in the agreement, and how to compare gases with different physical properties? How to ensure the compatibility of net zero emissions with the other objectives of the Paris Agreement? This article discusses possible choices and their implications, in order to provide useful recommendations for clarifying and operationalizing the global objectives of the Paris Agreement. (authors)