And according to the Planetary Boundaries concept, the nitrogen cycle is already one of the places where humanity has already broken through the "safe limit".

BBC: Food: Organic growth?

Planetary boundaries provide a useful way of thinking about environmental change, because in many cases they give scope for further change that has not already happened.

ECONOMIST: The global environment

The vision aims to eradicate poverty, reduce inequality, make growth inclusive, and production and consumption more sustainable, while combating climate change and respecting a range of other planetary boundaries.

UNESCO: CULTURE

The story beginning overleaf assesses the implications for marine biodiversity of transgressing planetary boundaries, due to human-induced changes to the climate system, pollution and ocean acidification, as well as more direct threats like invasive species, overfishing and habitat destruction.

UNESCO: Open Access to Scientific Information

The planetary-boundaries idea seeks to constrain the Anthropocene within the norms of the Holocene.

ECONOMIST: The global environment

The second is that the planetary-boundaries group derives most of its limits by looking at conditions during the Holocene the epoch since the end of the most recent ice age, in which human civilisations have grown up.

ECONOMIST: The global environment

Researchers must identify the planetary and regional thresholds and boundaries that, if crossed, could result in serious social, economic and environmental crises.

UNESCO: Social and Human Sciences

This recognition has led researchers to take the first step to identify planetary and regional thresholds and boundaries that, if crossed, could generate unacceptable environmental and social change.

UNESCO: Social and Human Sciences