Earth pushed to breaking point, says new study in Science journal

At the rate things are going, the earth in the coming decades could cease to be a "safe operating space" for humans.

That is the conclusion of a paper published in the journal Science by 18 researchers trying to gauge the breaking points in the natural world.

The paper contends that we have already crossed four "planetary boundaries". They include the extinction rate; deforestation; the level of carbon dioxide in the atmosphere; and the flow of nitrogen and phosphorous (used on land as fertiliser) into the ocean.

"What the science has shown is that human activities - economic growth, technology, consumption - are destabilising the global environment," said lead author Will Steffen, who holds joint appointments at the Australian National University and the Stockholm Resilience Centre.

These were not future problems, but rather urgent matters, according to Steffen, who said that the economic boom since 1950 and the globalised economy have accelerated the transgression of the boundaries. No one knows exactly when push would come to shove, but he said the possible destabilisation of the "earth system" as a whole could occur in a time frame of "decades out to a century".

The researchers focused on nine separate planetary boundaries first identified by scientists in a 2009 paper. These set theoretical limits on changes to the environment, and include ozone depletion, freshwater use, ocean acidification, atmospheric aerosol pollution and the introduction of exotic chemicals and modified organisms.

Beyond each planetary boundary is a "zone of uncertainty". This zone is meant to acknowledge the inherent uncertainties in the calculations, and to offer decision-makers a bit of a buffer, so that they can potentially take action before it's too late to make a difference. Beyond that zone of uncertainty is the unknown - planetary conditions unfamiliar to us.