Hugh Pickens writes "The UC Berkeley News Center reports that a prestigious group of 22 internationally known scientists from around the world is warning that population growth, widespread destruction of natural ecosystems, and climate change may be driving Earth toward an irreversible change in the biosphere, a planet-wide tipping point that would have destructive consequences absent adequate preparation and mitigation. 'It really will be a new world, biologically, at that point,' warns lead author Anthony Barnosky. '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.' 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. Humans have already converted about 43 percent of the ice-free land surface of the planet to uses like raising crops and livestock and building cities. This situation typically is accompanied by species extinctions and a loss of biodiversity. 'My view is that humanity is at a crossroads now, where we have to make an active choice,' says Barnosky. 'One choice is to acknowledge these issues and potential consequences and try to guide the future (in a way we want to). The other choice is just to throw up our hands and say, 'Let's just go on as usual and see what happens.'"