Reply to: Concerns regarding proposed groundwater Earth system boundary

REPLYING TO: M. O. Cuthbert et al. Nature https://doi-org.ezp.sub.su.se/10.1038/s41586-024-08082-9 (2024).

Groundwater is widely used for domestic and agricultural purposes, but is subject to increasing risks from overexploitation. Responding to this global significance, we recently defined a safe and just Earth system boundary (ESB) for groundwater and, in the absence of a consistent data source on baseline aquifer volumes, used derived estimates of groundwater storage (GWS) from the Gravity Recovery and Climate Experiment (GRACE) satellite mission data to assess the state of the Earth system with respect to the ESB for groundwater. In the accompanying Comment, Cuthbert et al. agree that our effort to define a groundwater ESB is timely and important, but they assert that our approach is “flawed, unsafe and unjust”. Their concerns reflect misunderstandings of the definition and purpose of the boundary, a misunderstanding of the ‘safe’ and ‘just’ concepts that underpin our work, a lack of confidence in the use of GRACE data to calculate changes in GWS, and the possibility of confusion related to the use of some terms.