The earth's environmental systems "are being pushed towards their biophysical limits", the United Nations Environment Program says.
In a 525-page report on the health of the planet, the agency paints a grim picture.
It says: "Several critical global, regional and local thresholds are close or have been exceeded.
"Abrupt and possibly irreversible changes to the life-support functions of the planet are likely to occur."
The report, which was released overnight, says changes include rising oceans, increased frequency and severity of floods and droughts, and the collapse of fisheries.
The report, which compiles three years of work by 300 scientists, says about 20 per cent of vertebrate species are under threat of extinction, coral reefs have declined by 38 per cent since 1980, greenhouse gas emissions could double over the next 50 years, and 90 per cent of water and fish samples are contaminated by pesticides.
It says little or no progress has been made over the past five years on nearly a third of the main environmental goals, including global warming. Significant progress has been made on just four of the 90 most important goals, the report says.
"This is an indictment," UNEP executive director Achim Steiner said at a news conference in Rio De Janeiro.
"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.
"Once the tipping point occurs, you don't wake up the next morning and say, 'This is terrible, can we change it?' We are condemning people to not having the choice.
"Change is possible. Given what we know, we can move in another direction."
The report was released in the run-up to the UN Rio+20 conference on June 20 and 21.