* EU, U.S. oppose call to assign historic responsibility for warming
* EU says could delay climate deal due in 2015
OSLO, Nov 15 (Reuters) - The European Union and the United States opposed on Friday a call by developing countries to measure each nation's historical responsibility for global warming to guide a U.N. deal in 2015 to cut future greenhouse gases.
Rich nations fear that any scientific study that might blame rich nations most since they have burnt fossil fuels since the Industrial Revolution could further delay sluggish U.N. talks.
Brazil won backing from more than 100 developing nations at the Nov. 11-22 meeting in Warsaw to ask the U.N.'s scientific panel of climate experts to look into each nation's share of past responsibility for spewing out greenhouse gases.
Such a study could then guide the new deal, due to be agreed in 2015 and to enter into force from 2020.
But it also risks opening a political and legal can of worms. Assigning "responsibility" could be taken as an admission of liability for causing more droughts, heatwaves, floods and rising sea levels.
"We are not finding a positive response on the side of the developed countries ... which is very surprising to us," Brazil's delegation leader José Antonio Marcondes de Carvalho told a news conference.
"Why are they rejecting to at least talk?" he said, adding the developed nations would continue to push the idea.
But the European Union said that a study might take too long and risked being too narrowly focused.
"We do fear the current proposal on the table carries a risk of politicising the process and missing the (2015) deadline," Juergen Lefevere, head of the European Commission delegation.
"The discussion should be about a much broader set of indicators, not just historical emissions," he said.
Other factors could include current and future emissions, projected economic growth, population growth, development needs, and the capacity and cost to cut emissions, he said.
China is the top annual emitter of greenhouse gases, ahead of the United States, the European Union, India and Russia.
And China's fast economic growth means that it is catching up with the United States and the European Union as the largest cumulative emitters since 1850.
That could profoundly affect its "historic" role.
The total share of global emissions from developing countries is likely to reach 51 percent by 2020, up from 48 percent now, according to the study by the PBL Netherlands Environment Assessment Agency, research group Ecofys and the European Commission's Joint Research Centre.
Niklas Hoehne, an author of the study at Ecofys, said the issue of historical responsibility boiled down to political choices rather than scientific ones.
Developing nations, for instance, argue that "historical responsibility" stretches right back to the Industrial Revolution.
Developed nations tend to say it should start only from the mid-1990s, when scientists first decided that the balance of evidence indicated that global warming was man-made.
"All the data is available," Hoehne said. "How it is interpreted is a political question."
(editing by Ron Askew)