UNITED NATIONS — More than 100 world leaders attending this month's Earth Summit must tackle the double threat of widespread poverty and increasing environmental devastation that has left billions of people facing food and water shortages, a new U.N. report said Tuesday.

The report reviews the most authoritative data from U.N. and international organizations about the use of natural resources and presents a sobering assessment of a planet in peril and in need of a massive global commitment to secure the future for the world's children.

According to its findings, forests are being destroyed, drought is becoming more intense, sea levels are rising, agricultural production can't keep up with the demand for food, many plant and animal species are at risk of extinction, and air and water pollution are killing millions of people.

"The real threat that we face now is the insidious global spread of poverty and environmental stress — and that is the real security threat that we need to address," said U.N. Undersecretary-General Nitin Desai, who will chair the Earth Summit in Johannesburg from Aug. 26 to Sept. 4. He told a news conference launching the report that there have been excellent small-scale initiatives to tackle many of the problems, and the great challenge of Johannesburg is to mobilize governments, voluntary organizations, and the private sector to implement these initiatives on a large scale.

Another challenge is to connect the agenda to preserve the world's natural resources with the goals adopted by more than 150 world leaders at the U.N. Millennium Summit in 2000, he said. Those goals include cutting the number of people living in poverty in half and giving every child an elementary school education by 2015. "You can't reduce poverty unless you also address land and water," Desai said. "You can't improve children's health without addressing sanitation and air quality."

The report by the U.N. Department for Economic and Social Affairs, which Desai heads, said the need to feed a rising global population — now more than 6 billion and projected to reach 8 billion by 2025 — is exacerbated by an increase in food consumption. At the same time, it said, the capacity to produce enough food is diminishing, especially in developing countries, and almost 800 million people are chronically undernourished, though the number is declining.

Desai said close to 30 percent of the 1.5 billion hectares of agricultural land in the world "is in some ways under stress — either soil erosion stress, salinity stress, even chemical pollution stress — and we have to address this."

The report found that global water use has increased sixfold over the last century, at twice the rate of population growth, and that agriculture represents 70 percent of this consumption. The greatest drain on the world's freshwater supplies is inefficient agricultural irrigation systems.

Meanwhile, about 40 percent of the world population — more than 2 billion people — face water shortages, and by 2025 that figure is expected to increase to 50 percent, the report said.

Signs of climate change linked to global warming are also taking a toll: droughts have increased in frequency and intensity in parts of Asia and Africa, and sea levels are rising, the report said.

Fossil fuel consumption and carbon emissions continued to rise in the 1990s, particularly in Asia and North America. Desai said another priority must be to promote renewable energy sources such as water, wind, and solar power.

During the 1990s, the report said, 220 million acres of forests — an area larger than Venezuela — was destroyed, almost all in tropical regions in Africa and Latin America.