The earth's environmental systems ``are being pushed towards their biophysical limits,'' beyond which loom sudden, irreversible and potentially catastrophic changes, the United Nations Environment Program warned Wednesday.

In a 525-page report on the health of the planet, the agency paints a grim picture:  The melting of the polar ice caps, desertification in Africa, deforestation of tropical jungles, spiraling use of chemicals and the emptying out of the world's seas are just some of myriad environmental catastrophes posing a threat to life as we know it.

``As human pressures on the earth ... accelerate, several critical global, regional and local thresholds are close or have been exceeded,'' the report says. ``Once these have been passed, abrupt and possibly irreversible changes to the life-support functions of the planet are likely to occur, with significant adverse implications for human well-being.''

Such adverse implications include rising sea levels, increased frequency and severity of floods and droughts, and the collapse of fisheries, said the report, which compiles the work of the past three years by a team of 300 researchers.

The bad news doesn't end there. The report says about 20 percent of vertebrate species are under threat of extinction, coral reefs have declined by 38 percent since 1980, greenhouse gas emissions could double over the next 50 years, and 90 percent of water and fish samples from aquatic environments are contaminated by pesticides.

It adds that of the 90 most crucial environmental goals, little or no progress has been made over the past five years on nearly a third of them, including global warming. Significant progress has been made on just four of the objectives, the report says.

``This is an indictment,'' UNEP executive director Achim Steiner said at a news conference in Rio De Janeiro, which is to host later this month a U.N. conference on development that protects the environment. ``We live in an age of irresponsibility that is also testified and documented in this report.