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.

Related: Most mammals won't flee climate change fast enough

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.

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

1. Qatar
2. Kuwait
3. United Arab Emirates
4. Denmark
5. United States
6. Belgium
7. Australia
8. Canada
9. The Netherlands
10. Ireland

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.

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