RIO DE JANEIRO >> 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.

“In 1992 (when the first of the agency’s five reports was released) we talked about the future that was likely to occur. This report 20 years later speaks to the fact that a number of the things that we talked about in the future tense in 1992 have arrived,” Steiner said. “Once the tipping point occurs, you don’t wake up the next morning and say, ‘This is terrible, can we change it?’ That is the whole essence of these thresholds. We are condemning people to not having the choice anymore.”  

Steiner called for immediate action to prevent continued environmental degradation, with its ever-worsening consequences.

“Change is possible,” he said, adding that the report includes an analysis of a host of environmental preservation projects that have worked. “Given what we know, we can move in another direction.”

The United Nations’ upcoming Rio+20 conference on sustainable development would be the ideal forum to spearhead the kind of global action that’s needed if the worst is to be avoided, Steiner said.

However, the run-up to June 20-21 conference has been plagued with problems, as developing and developed countries continue to bicker over what the objectives of the event should be.

Speaking in New York on Wednesday, U.N. Secretary-General Ban Ki-moon acknowledged that negotiations on a final document for the conference have been “quite difficult” but he said he was “cautiously optimistic” that the 193 U.N. member states will reach agreement.

“We live in a world of economic uncertainty, growing inequality and environmental decline,” Ban told a news conference at U.N. headquarters. “This (conference) is a once in a generation opportunity. … We need leaders to have political commitment and political courage and vision. Short-term measures will not be the answers. You need to have mid- and longer-term visions for sustainable development.”

UNEP spokesman Nick Nuttall said the agency deliberately scheduled the release of its report to coincide with the run-up to the conference.

“It tells, we hope in a polite way, but in a scientifically honest way, world leaders who are coming in a few weeks’ time why they are coming and why they need to define an impressive outcome for everybody in the world,” Nuttall said at the Rio news conference.

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Associated Press writer Edith M. Lederer at United Nations headquarters contributed to this report.