"It's not just a question of throwing more money at the problem," the UN's climate change chief, Yvo de Boer, told Reuters.

"(It's) incredibly important to put in place policies and measures that guide those investments in the right direction."

The report said emissions have to drop in the next 25 years to 2004 levels. Some 68 percent of emissions cuts must take place in developing countries, it added.

The fight against global warming has two parts, curbing the greenhouse gas emissions which are causing the problem, and preparing for climate change that is now unavoidable.

Curbing greenhouse gas emissions alone will cost some $210 billion annually by 2030, through measures such as investing in energy efficiency and low-carbon renewable energy, the report said.

"To meet the main part of this goal of returning emissions to 2004 (levels) by 2030, you don't mainly need extra money but a shift in investments away from building new power generating capacity towards improving energy efficiency," said de Boer.

Adapting to climate change was more difficult to estimate, but would run into several tens of billions of dollars annually by 2030.

Emissions of the commonest greenhouse gas carbon dioxide are rising in large part because developing countries like China and India are fuelling rapid economic growth by burning coal.

China will likely overtake the United States as the world's biggest carbon emitter this year, if it hasn't already done so, analysts say.

The answer is both foreign aid for the world's poorest nations, and domestic action such as eliminating policies which favour fossil fuels over renewable energy, the UN report said.

Another solution was carbon trading, whereby rich countries meet domestic emissions goals by buying carbon offsets from developing nations.

"It's a question of putting in place smart policies ... including, very significantly, the carbon market," said Yvo de Boer, who is head of the UN body which administers carbon trading under the Kyoto Protocol.

Thursday's report estimated carbon trading could deliver between 400 million and 6 billion tonnes annual greenhouse gas emissions cuts, in carbon dioxide equivalent, by 2030. At present Germany has annual emissions of 1 billion tonnes.