A building under construction is seen amidst smog on a polluted day in Shenyang, Liaoning province November 21, 2014.REUTERS/Jacky Chen ROME, Jan 15 - Human activity has pushed the planet across four of nine environmental boundaries, sending the world towards a "danger zone", according to a study published on Thursday in the journal Science. Climate change, biodiversity loss, changes in land use, and altered biogeochemical cycles due in part to fertiliser use have fundamentally changed how the planet functions, the study said.