Mexican President Felipe Calderon said Saturday that upcoming climate change talks in Mexico will produce "unprecedented results" but not a hoped-for legally binding treaty.
Later this month 194 countries will meet in the Mexican resort city of Cancun for a second attempt at hammering out an agreement to curb greenhouse gases after 2012, when the current arrangement expires.
The climate gathering takes place in the shadow of last December's Copenhagen summit, which ended in failure after China was accused of blocking a deal on binding commitments.
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"There are reasons that allow us to be moderately optimistic about what is going to happen there (in Cancun)," Calderon said in a speech to a business conference ahead of a Pacific Rim summit in Japan.
"It is not possible to expect the founding treaty of the future (with) the legally binding commitments that we all want," he said on the sidelines of the Asia Pacific Economic Cooperation (APEC) talks.
"The good news is that Cancun will certainly make unprecedented results in my opinion."
"We may not score a touchdown in Cancun but we will certainly make a significant first down with a very important advance in the negotiations," he said, using an American football analogy.
In Seoul on Friday, the world's 20 largest rich and emerging economies including China vowed to "spare no effort" at the Cancun talks, which run from November 29 to December 10.
However, China has routinely voiced reluctance to take the lead in curbing greenhouse gases, saying it is not to blame for the situation the world is in.
China and the United States clashed at a UN climate gathering last month in the Chinese city of Tianjin, accusing each other of blocking progress ahead of Cancun.
The United States wants China, the world's largest source of the greenhouse gases blamed for climate change, to commit to curbing carbon emissions and developing countries to agree to more scrutiny of their climate claims.
China has rejected pressure for outside verification, saying it is a US attempt to divert attention from the fact the United States has so far failed to get emissions-cut legislation through Congress.
As the prospect of a path-breaking deal in Cancun has dimmed, efforts have moved towards more modest and incremental steps.
