Population growth and unsustainable consumption are driving Earth towards "unprecedented" environmental destruction, the UN said in a report Wednesday ahead of the Rio Summit.

Of 90 key goals to protect the environment, only four have seen good progress, the United Nations Environment Programme (UNEP) said in a planetary assessment issued only every five years.

"If current trends continue, if current patterns of production and consumption of natural resources prevail and cannot be reversed and 'decoupled,' then governments will preside over unprecedented levels of damage and degradation," said UNEP Executive Director Achim Steiner.

The phonebook-sized report, the fifth edition of the Global Environment Outlook (GEO), was issued ahead of the June 20-22 UN Conference on Sustainable Development -- the 20-year follow-up to the landmark Earth Summit, also in Rio.

Preceded by a series of forums gathering as many as 50,000 policymakers, business executives and activists, the summit aims at plotting a course for green development over the next two decades.

But the report warned of many challenges, painting a tableau of a planet whose resources were being stressed into the red zone.

Since 1950, the world's population has doubled to seven billion and is on course for around 9.3 billion by 2050 and some 10 billion by 2100.

At the same time, use of natural resources has zoomed as emerging countries follow rich economies in a lifestyle that is gluttonous on energy and use of water, habitat and fisheries.

"The scale, spread and rate of change of global drivers are without precedent. Burgeoning populations and growing economies are pushing environmental systems to destabilizing limits," said the report.

It analyzed 90 objectives for the environment identified by UN members.

Only four have seen significant progress: scrapping CFC chemicals that damage Earth's protective ozone layer; removing lead from fuel; increasing access to clean water for the poor; and boosting research to reduce marine pollution.

In 40 goals that UN member states asked to be monitored, there was "some" progress, such as expanding national parks and tackling deforestation.

But there was little or no progress in 24 others, including curbing climate change, fisheries depletion and desertification.

"The scientific evidence, built over decades, is overwhelming and leaves little room for doubt," Steiner told a press conference in Rio.

"The moment has come to put away the paralysis of indecision, acknowledge the facts and face up to the common humanity that unites all peoples," he said.

"Rio+20 is a moment to turn sustainable development from aspiration and patchy implementation into a genuine path to progress and prosperity for this and the next generations to come."

For climate change, the last decade was the warmest on record, and in 2010 emissions from fossil fuels were the highest ever.

"Under current models, greenhouse-gas emissions could double over the next 50 years, leading to (a) rise in global temperature of three degrees Celsius (5.4 degrees Fahrenheit) or more by the end of the century," UNEP said.

"The annual economic damage from climate change is estimated at 1-2 percent of world GDP by 2100 if temperatures increase by 2.5 C (4.5 F)," it warned. The UN's target is 2 C (3.6 F).

However, there have been gains in energy efficiency and "some progress" towards meeting emissions targets under the Kyoto Protocol, UNEP said.

For eight goals, including preservation of the coral reefs, things have deteriorated.

The world fell far short of meeting a Millennium Development Goal (MDG) of significantly reducing destruction of biodiversity by 2010.

"Around 20 percent of vertebrate species are under threat," said UNEP.

"The extinction risk is increasing faster for corals than for any other group of living organisms, with the condition of coral reefs declining by 38 percent since 1980. Rapid contraction is projected by 2050."

Data was insufficient to enable a judgment on the 14 other goals.

The GEO report proposed a panoply of remedial measures for Earth's population to start living within its means, including more efficient use of energy and eco-friendlier resources.

Also important was to redefine human progress so that it goes beyond the simple yardstick of economic growth to included quality of life issues.

The Rio Summit is to assess progress since the 1992 Earth Summit, considered a landmark for creating awareness on climate change and biodiversity.

Among ideas that are being debated for the summit is to set down "Sustainable Development Goals" that would succeed the MDGs when their deadline comes up in 2015.