Two documents totalling 68 pages also laid out choices on controversial issues such as nuclear power, emissions trading, forests, shipping or aviation in a new UN global warming pact due to be agreed in Copenhagen in December.

"Key UN negotiating texts, which will form the basis of an ambitious and effective international response to climate change...are now available," the UN Climate Change Secretariat said in a statement on its website.

Negotiators say little has been agreed in talks launched in late 2007 -- the tough decisions will be made in Copenhagen.

One text outlined ranges for cuts in greenhouse gases by industrialised countries beyond 2012 under a successor to the Kyoto Protocol. Kyoto binds 37 nations to cutemissions by an average of 5 percent below 1990 levels by 2008-12.

One suggestion is for rich nations to more than halve their emissions below 1990 levels by 2018-2022 to rein in global warming that the U.N. Climate Panel says will cause rising sea levels, heatwaves, floods and droughts.

Such deep cuts -- favoured by some developing countries which blame the rich for causing global warming since the Industrial Revolution -- are far bigger than those foreseen by developed nations struggling with economic recession.

President Barack Obama, for instance, aims by 2020 to cut U.S. emissions to 1990 levels, about 14 percent below 2007 levels.

A separate U.N. draft looking at possible actions by developing nations, led by China and India, will be published on May 18. All texts will discussed at a next set of U.N. climate change talks in Bonn from June 1-12.

"It's certainly a big moment for the talks," Yvo de Boer, head of the Secretariat, told Reuters on Tuesday when asked about the publications.

"The texts will provide governments with the basis to get down to the real nitty gritty of identifying where they agree, where they disagree and what they can do to turn disagreement into an agreement," he said.

Friday's texts outline possible ways of widening a scheme that allows developed nations to claim carbon trading credits from green investments in poor countries, for instance in hydropower or wind farms.

Some countries would like to see such credits expanded to nuclear power plants or to projects to capture and bury heat-trapping carbon dioxide released by burning fossil fuels in power plants or oil refineries. Others are strongly opposed.

Three options for nuclear power and carbon capture were acceptance, rejection or shelving decisions until 2010 or 2011.

The documents also lay out options on how to account for forestry or land use changes in developed nations -- plants soak up carbon dioxide as they grow and release it when they decay or are burnt.

And the texts include proposals by the European Union to add international shipping or aviation to carbon trading schemes. Fuel burnt on planes and ships on international routes are exempt under Kyoto.