As researchers studying the concept of setting environmental boundaries for planetary well-being (J. Rockström et al. Ecol. Soc. 14, 32; 2009), we disagree with Simon Lewis's suggestion that there are flaws in these proposals (Nature 485, 417; 2012).
Lewis contends that the concept's focus is too narrow, that it doesn't distinguish between 'boundaries' and 'thresholds' and that it should clarify the influence of scale on different problems. These are misunderstandings.
Planetary boundaries are not fixed 'supply limits', but are set within a safety margin around complex thresholds that are intertwined at regional and global scales. Ecosystem changes caused by nitrogen pollution, for example, are driven by global trade and cannot be uncoupled from climate change and alterations in land use. Also, investment in new phosphorus technologies can address the problems of both pollution and stock control.
It is a mistake to see the setting of environmental boundaries as a call for multilateral negotiations around static limits. They are instead a bid to reform environmental governance at multiple scales. Scientific assessment, institutional interaction and social–ecological innovation will enable us to work more effectively towards planetary stewardship.