VIENNA — The climate rule book being drafted to keep a lid on Earth's rising temperatures should be finished by the end of the year — with or without the U.S. government's help.

Countries that ratified the Paris climate agreement will meet in December in Poland, where they're expected to put the finishing touches on transparency and verification measures ensuring industries and economies abide by emission rules. It's not yet clear how deeply the world's second-biggest greenhouse gas emitter will engage in the process after President Donald Trump announced his intention to withdraw the U.S. from the accord, said the United Nations' top climate official.

"The urgency of the issue, the high expectations that are around the process are putting strong pressure on the parties to really find ways of coming to compromises," Patricia Espinosa said. "It would be very difficult for any party to bear the responsibility of having obstructed an agreement."

Scientists predict higher frequencies of floods, famines and superstorms unless the world keeps temperature rises well below 3.6 degrees Fahrenheit this century. The risks posed by runaway climate change have mobilized trillions of dollars of investments by companies and economies transitioning to renewable energy, electric transport and more efficient technologies. The U.S. became the only major economy outside the deal in November and has pledged to double down on coal power, the world's biggest source of carbon emissions.

"I very much hope that we can engage with the U.S. administration, that we can address their concerns, their doubts about the commitments to the Paris Agreement," said Espinosa, a career diplomat from Mexico who heads the UN's Framework Convention on Climate Change. "I hope there will be time for reconsideration. We certainly don't want to see them depart from the Paris agreement."

Other countries don't have "any appetite" to reopen negotiations on the Paris accord, Espinosa said. Instead, they're concentrating on the painstaking task of writing the detailed rules that will bind countries to the agreement.