Overconsumption has led to an estimated 33 percent decline in the natural wealth of the world’s ecosystems over the past 30 years, according to a report released by the World Wildlife Fund on Friday. If current patterns continue, humans would need an additional two planets in order to survive, WWF said. The group measured the “ecological footprint” of various countries — their per capita consumption of food, materials, and energy — and found, not surprisingly, that the footprints of rich nations are about four times larger than those of small nations. The United Arab Emirates, Singapore, and the U.S. have the biggest footprints, while Namibia, Bangladesh, Afghanistan, and Eritrea have the smallest. “It is the consumers of the rich nations of the temperate northern regions of the world who are primarily responsible for the ongoing loss of natural wealth in the tropics,” said Jonathan Loh, editor of the report.