At the rate things are going, the Earth in the coming decades could cease to be a â€œsafe operating spaceâ€ for human beings. That is the conclusion of a new paper published Thursday 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 â€œplanetary boundaries.â€ They are the extinction rate; deforestation; the level of carbon dioxide in the atmosphere; and the flow of nitrogen and phosphorous (used on land as fertilizer) into the ocean.
â€œWhat the science has shown is that human activities â€” economic growth, technology, consumption â€” are destabilizing the global environment,â€ said Will Steffen, who holds appointments at the Australian National University and the Stockholm Resilience Center and is the lead author of the paper.
These are not future problems, but rather urgent matters, according to Steffen, who said that the economic boom since 1950 and the globalized economy have accelerated the transgression of the boundaries. No one knows exactly when push will come to shove, but he said the possible destabilization of the â€œEarth Systemâ€ as a whole could occur in a time frame of â€œdecades out to a century.â€
The researchers focused on nine separate planetary boundaries first identified by scientists in a 2009 paper. These boundaries 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 â€œzone of uncertainty.â€ 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 itâ€™s too late to make a difference. Beyond that zone of uncertainty is the unknown â€” planetary conditions unfamiliar to us.
â€œThe boundary is not like the edge of the cliff,â€ said Ray Pierrehumbert, an expert on Earth systems at the University of Chicago. â€œTheyâ€™re a little bit more like danger warnings, like high-temperature gauges on your car.â€