Human-driven activities have pushed Earth into the “danger zone” for planetary health, according to research that seeks to understand how far people can stress the limits of the world’s ability to handle anthropogenic impacts without disastrous results.

Fourteen years after establishing nine “planetary boundaries” – defined as “processes that are critical for maintaining the stability and resilience of Earth system as a whole” – researchers say humanity has pushed six of those nine systems past safe limits.

Those systems include: biodiversity, climate change, land and freshwater impacts, biogeochemical cycles, and synthetic chemicals and substances like microplastics; a seventh, ocean acidification, is nearing its boundary. Conversely, the ozone layer – which was in crisis in the 1990s – is now on track to completely recover after concerted global cooperation resulted in the Montreal Protocol, banning ozone-depleting substances.

“We don’t know that we can thrive under major, dramatic alterations of our conditions,” lead author Katherine Richardson of the University of Copenhagen told a news conference Wednesday. “We can think of Earth as a human body, and the planetary boundaries as blood pressure. Over 120/80 does not indicate a certain heart attack but it does raise the risk.”

(APThe GuardianReutersBloomberg $, CNNScientific AmericanSalon. Study: ScienceAdvances)