The United States will stay out of any deal to curb emissions of global-warming gases unless countries like China and India join, a prominent Democratic senator said Thursday, according to dpa. Senator John Kerry's remarks during a UN climate conference injected caution into hopes pinned on president-elect Barack Obama, who has pledged to make the United States a leader in fighting climate change. "The United States will assume its responsibilities - I am confident - for mandatory reductions," Kerry told reporters. "But we will not pass a treaty unless it is a global solution." Any global warming treaty requires approval by two-thirds of the 100 US senators. Kerry traveled to Poznan, Poland, for the finale of this year's main UN climate meeting, where nations are setting the course for tough negotiations on an emissions-cutting accord due next December. He said he would report to Obama on his talks, which included meetings Thursday with officials from China and Sweden and UN Secretary General Ban Ki-moon. Kerry's comments gave a sense of where US debate on global warming may head after Obama's planned January 20 inauguration. "All countries need to be on notice," said Kerry, who ran for president in 2004 and is set to chair the Senate Foreign Relations Committee. He mentioned China and India, two key countries not covered by binding emissions cuts under the UN treaty known as the Kyoto Protocol. China has surpassed the US as the biggest emitter of greenhouse gases by some measures. Obama, a Democrat, has energized global climate talks with promises to take US policy far beyond efforts during President George W Bush's eight years in office. He has pledged to cut US emissions to 1990 levels by 2020 and to launch a nationwide system of trading in emissions permits. He has a Democratic majority in both houses of Congress. Obama's arrival is also likely to spark cooperation on climate change with European governments, Kerry said. "Europe is a vital partner," he said. "I think Europe has been waiting with bated breath for some period of time for someone to partner with." Kerry said the US Congress is committed "to move on mandatory goals as rapidly as possible," with the exact levels to be determined. He suggested that an emissions trading plan, known as cap-and-trade, would be slower to emerge. He said the world is emitting carbon dioxide, the main global- warming gas, four times faster than in 1990. He pointed to a scenario of rising global temperatures well beyond what scientists have identified as safe. "That is beyond unacceptable - that is catastrophic in its implications," he said.