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. [50 Amazing Facts About Earth]

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. (The organization Global Footprint Network marks "Earth Overshoot Day" every year to draw attention to how fast humans use natural resources. In 2011, Earth Overshoot Day fell on Sept. 27, the day humans used up Earth's annual resources.)

The report scientists calculated the world's hogs when it comes to resources (called the ecological footprint) by determining each nation's productive land capacity and comparing it to the actual population and consumption per person. The United States has the fifth-largest ecological footprint of any nation on Earth, according to the report.

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In order from most to least, the top 10 greediest resource users per capita are:

Qatar Kuwait United Arab Emirates Denmark United States Belgium Australia Canada The Netherlands Ireland

[See full list of top and bottom resource users]

Struggling species

All of this resource use is taking a toll. The Living Planet report also tracks biodiversity and species populations across the globe. This year's report details a startling loss of biodiversity around the globe: A loss of 30 percent of biodiversity on average, meaning a major decline in the number of different species of plants, animals and other organisms. Temperate species are doing relatively well, Loucks said, but tropical species have declined by 60 percent since the 1970s. Freshwater tropical species are the hardest-hit, having declined by 70 percent in that time period.

Globally, terrestrial species declined by 25 percent between 1970 and 2008, WWF reports. Marine (non-freshwater) species declined by 20 percent.

Many of the group's proposed solutions to humanity's out-of-control resource use center around Rio+20, the upcoming United Nations Conference on Sustainable Development set for June 20, 2012. The meeting is designed to help create pathways for sustainable development in the future, said Kate Newman, WWF's managing director of public sector initiatives. She cited the example of Mozambique, a poor country that may be home to one of the largest natural gas fields in the world. As international companies arrive to exploit this resource, local planners are concerned about how to make sure the entire nation benefits, she said.

In the same way, global decision-makers need to think long-term, Loucks said.

"As we're approaching a planet with 9 billion people on it, we need to find a global solution," he said. "The challenge for us is this is a long-term problem. This is the Earth for millennia. We need to move beyond the election cycle, beyond the quarterly report cycle."

You can follow LiveScience senior writer Stephanie Pappas on Twitter @sipappas. Follow LiveScience for the latest in science news and discoveries on Twitter @livescience and on Facebook.

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