LONDON: Prime Minister Gordon Brown said securing a deal on climate change was going to be "very difficult," as he arrived in Copenhagen late Tuesday for the crunch talks. But Brown said he was determined to work with all countries to get the job done, despite the "many issues to be sorted out" at the UN summit in the Danish capital ahead of the Friday deadline. "I accept it?s very difficult for ... there are a number of problems that still have got to be sorted out, but we will be doing everything we can," Brown told the BBC. "We will be working with all countries to make sure we get an agreement, and I?m determined to use all my efforts over the next few days, with meetings tonight and early tomorrow morning, to get the agreement that we need." He also said: "It?s possible that we will not get an agreement and it?s also true that there are many issues to be sorted out." UN chief Ban Ki-moon earlier urged world leaders to put aside selfish national interest and halt the juggernaut of climate change. But China and the United States -- the world's two biggest carbon polluters -- brushed aside European calls for concessions on emissions reductions, the thorniest issue of all. The summit aims to seal national pledges to curb the heat-trapping carbon gases that cause climate change, and set up a mechanism to provide billions of dollars for poor countries facing worsening drought, flood, and rising seas. Brown earlier said he "wholeheartedly" supported proposals put forward during a meeting with Ethiopian Prime Minister Meles Zenawi to assist African nations in meeting the challenge of global warming. Brown also slammed climate change skeptics, saying the consequences of global warming were already hitting Africa. "Climate change in Africa is not a matter of dispute between science and pernicious ignorance," he said in a statement released by Downing Street. "It is happening now, felt every day by millions of people as drought and water scarcity and visibly changing seasons."