The world\'s biodiversity is down 30 percent since the 1970s, according to a new report, with tropical species taking the biggest hit. And if humanity continues as it has been, the picture could get bleaker. Humanity is outstripping the Earth\'s resources by 50 percent — essentially using the resources of one and a half Earths every year, according to the 2012 Living Planet Report, produced by conservation agency the World Wildlife Fund (WWF). Colby Loucks, the director of conservation sciences at WWF, compared humanity to bad houseguests. \"We\'re emptying the fridge, we\'re not really taking care of the lawn, we\'re not weeding the flower beds and we\'re certainly not taking out the garbage,\" Loucks said. Burning through resources The biannual Living Planet report is designed to call attention to the Earth\'s \"invisible economy,\" said Emily McKenzie, the director of the WWF\'s Natural Capital Program. Natural resources — and the rate at which humans burn through them — rarely appear on policymakers\' balance sheets, McKenzie said. But humanity is essentially in debt to Mother Earth, conservationists find. As of 2008, the most recent year for which data is available, humans were outstripping Earth\'s biocapacity by 50 percent. Biocapacity is the amount of renewable resources, land, and waste absorption (such as sinks for carbon dioxide) the Earth can provide. In other words, it takes the planet 1.5 years to restore what humanity burns through in a year.