Reactions to the first draft text released over the weekend were measured. The outlines left many options open and did not suggest any timeline for governments to reach a final, legally binding global treaty.

Government ministers will be arriving in Mexico this week to begin the earnest phase of a U.N. climate summit and thrash out a package of measures to confront global warming.

Negotiators from more than 190 countries have already been in Mexico’s Cancun since November 29, and voiced some optimism that they are making progress. Ministers arrive Tuesday, looking to turn that progress into a concrete deal by the summit’s end on Friday.

Agreeing on a new global treaty that would curb climate change was never in the cards in Cancun, but governments and environmentalists have hoped for movement on some of the building blocks of a treaty that failed at last December’s U.N. summit in Copenhagen.

“The pressure is very high” on governments, said Artur Runge-Metzger, the European Union’s chief negotiator.

Reactions to the first draft text released over the weekend were measured. The outlines left many options open and did not suggest any timeline for governments to reach a final, legally binding global treaty. Some have pushed for a deadline of the end of 2011.

“There are a lot of options in the text that we generally support, and we ask negotiators to go for the strong options,” said Gordon Shepherd of the World Wildlife Fund.

Among the text’s proposals was a review to see whether countries’ actions to cut greenhouse-gas emissions were enough to avert climate change’s worst consequences by keeping global temperatures from rising more than 2 degrees Celsius.

Governments first laid out plans to cut emissions at last year’s Copenhagen summit. Environmentalists complained the new Cancun text did not recognize existing U.N. studies showing countries’ efforts to date have fallen far short of meeting that temperature goal.

A final deal will likely rest with the United States and China, the world’s two largest emitters. U.S. officials last week spoke of progress in talks with China and said they believed a final package would be agreed by the summit’s end. China signalled a willingness to open up its own actions on climate change to increased international scrutiny, a key U.S. demand.

But Japan, Russia and Canada dealt a blow to the conference by opposing a renewal of the Kyoto Protocol unless the United States and China sign onto a new accord.

Kyoto, which targets greenhouse-emissions of industrial nations, expires in 2012. Developing countries, including China, have insisted it be renewed before they consider an accord that would clamp down on their own emissions.

There is also an expectation that ministers will close deals on setting up key mechanisms for tackling climate change. That includes a Green Fund to help poor countries deal with warming, an incentives programme to tackle deforestation, and a network of technology centres to improve cooperation on new forms of renewable energy.

But Greenpeace warned over the weekend that the deforestation programme was being watered down, and it also singled out an effort to include clean-coal projects in developing countries as part of aid that wealthy countries are providing to tackle global warming.

Controversial technologies to sequester the carbon dioxide emissions from coal plants have been slammed as merely a dream by some environmentalist groups, including Greenpeace. Others have said efforts to produce “clean coal” will be an essential part of the climate puzzle in the years to come.