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€
ON NOVEMBER 2ND the Intergovernmental Panel on Climate Change (IPCC), which represents mainstream scientific opinion, said that it was extremely likely that climate change is the product of human activity. Extremely likely in IPCC speak means having a probability of over 95%. The claim forms part of its fifth assessment on the state of the global climate. In its first assessment, in 1990, the IPCC had said that “the observed increase [in air temperatures] could be largely due to natural variability.” Why have climate scientists become so much more certain that climate change is man-made, not natural?
Many factors influence the climate but perhaps the single most important is carbon dioxide (COâ‚‚). COâ‚‚ absorbs infra-red heat at a constant rate and at a higher rate than nitrogen and oxygenâ€”the main constituent parts of the atmosphereâ€”so the more COâ‚‚ in the air, the more the atmosphere will tend to warm up. Scientists attribute climate change to human activity mainly because people have been responsible for large increases in COâ‚‚. At the start of the industrial revolution, in about 1800, there were 280 parts per million (ppm) of COâ‚‚ in the atmosphere. That had been the level for most of human history. This year, however, concentrations exceeded 400 ppm, the first time it had reached that level for a million years.
Most of the increase has been caused by people burning fossil fuels. In the United States, for example, 38% of the COâ‚‚ produced in 2012 came from generating electricity and 32% came from vehicle emissions (the rest came from industrial processes, buildings and other smaller COâ‚‚ production). People also produce COâ‚‚ when they cut down forests for farmland and pasture