The international community began a meeting Monday in Cancun for the U.N. Framework Convention on Climate Change.
World leaders are calling for a balanced set of decisions to find a common environmental agreement at the climate summit.
EU delegates downplayed the potential for a climate alliance with Beijing, noting pledges of support often conflict with reality.
"I'm not sure it's that easy," European Climate Action Commissioner Connie Hedegaard was quoted by EUobserver as saying. "There are many parties that we have to cooperate with."
Environmental advocates say it's up to the largest markets -- the EU, China and the United States -- to lead a low-carbon market. But the midterm elections in the United States brought many Republican lawmakers to office, whose constituency, a Pew research poll found, tends to not believe in man-made climate change.
Jason Anderson, an activist with the World Wide Fund for Nature, said the biggest world markets need the most pressure at Cancun.
"The biggest emitters -- China and the U.S. -- are the biggest players," he told EUobserver. "The key question at the moment is how to bring pressure on the United States."