* U.N. has year-end deadline to agree 'rule book'
* G20 members, except United States, sign declaration of support
* Brazil pulls out of hosting 2019 talks
By Barbara Lewis and Anna Koper
KATOWICE, Poland, Dec 2 (Reuters) - Delegates from nearly 200 nations on Sunday began two weeks of talks to tackle deep political divisions at the most important U.N. meeting on global warming since the landmark 2015 Paris deal to shift away from fossil fuels.
Expectations are low that negotiations in Katowice, at the heart of Poland's coal region, will be sufficient to address concerns laid out in reports over recent weeks on the severity of rising greenhouse gas emissions.
The political climate has also been transformed since the Paris agreement and the fragile global unity that brought about that accord has shattered.
Fijian Prime Minister Frank Bainimarama declared the U.N. conference open on Sunday and handed over the presidency of the talks to Michal Kurtyka, Poland's deputy environment minster.
"We will all have to show creativity and flexibility," Kurtyka said.
Stoking the tensions, Brazil has gone back on an earlier promise to host next year's U.N. climate conference.
The United States, meanwhile, reiterated at the G20 summit in Argentina on Saturday its decision to withdraw from the Paris accord and a U.S. commitment to using all energy sources.
The other members of the group of industrialised nations - including the biggest polluter, China - reaffirmed their commitment to implementing the Paris deal, taking into account their national circumstances and relative capabilities.
The Katowice talks precede an end-of-year deadline to produce a "rule book" to flesh out the broad details that were agreed in Paris, aimed at limiting the rise in global temperatures to between 1.5 and 2 degrees Celsius.
To give the negotiations a better chance, the start of the Katowice talks was brought forward by a day.
Poland is hosting U.N. climate negotiations for a third time, but the nation remains hooked on coal, the most carbon-intensive fossil fuel. Coal provides about 80 percent of Poland's power and has been a major source of employment and national pride.
The younger generation is less emotionally attached to coal and is increasingly environmentally aware, though any phasing out of the fuel in Poland is likely to be slow.
The energy ministry said only last week that the country plans to invest in new coal capacity while its long-term energy strategy assumes it will still obtain about 60 percent of its power from coal in 2030. (Additional reporting by Wojciech Zurawski Editing by David Goodman)
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