When disturbance of local ecosystems exceeds 50% they may suddenly collapse into simpler, less biodiverse systems with the loss of many species. An interdisciplinary team of scientists published a report in Nature today warning that they have found evidence that the global ecosystem can transition the same way with potentially catastrophic consequences for human populations. The scientists aren't able to predict when the transition will happen because it happens suddenly at some point from 50% to 90%. Presently 43% of earth's land surface has been changed to urban or agricultural use and much of the rest is fragmented by roads.
Localized ecological systems are known to shift abruptly and irreversibly from one state to another when they are forced across critical thresholds... the global ecosystem as a whole can react in the same way and is approaching a planetary-scale critical transition as a result of human influence.
“It really will be a new world, biologically, at that point,” warns Anthony Barnosky, professor of integrative biology at the University of California, Berkeley, and lead author of a review paper appearing in the June 7 issue of the journal Nature. “The data suggests that there will be a reduction in biodiversity and severe impacts on much of what we depend on to sustain our quality of life, including, for example, fisheries, agriculture, forest products and clean water. This could happen within just a few generations.”When the tipping point is crossed it could be similar to a collapse described by Jared Diamond in his book, but on a global scale.
The authors note that studies of small-scale ecosystems show that once 50-90 percent of an area has been altered, the entire ecosystem tips irreversibly into a state far different from the original, in terms of the mix of plant and animal species and their interactions. This situation typically is accompanied by species extinctions and a loss of biodiversity.Currently, to support a population of 7 billion people, about 43 percent of Earth’s land surface has been converted to agricultural or urban use, with roads cutting through much of the remainder. The population is expected to rise to 9 billion by 2045; at that rate, current trends suggest that half Earth’s land surface will be disturbed by 2025. To Barnosky, this is disturbingly close to a global tipping point.
“Can it really happen? Looking into the past tells us unequivocally that, yes, it can really happen. It has happened. The last glacial/interglacial transition 11,700 years ago was an example of that,” he said, noting that animal diversity still has not recovered from extinctions during that time. “I think that if we want to avoid the most unpleasant surprises, we want to stay away from that 50 percent mark.”