LONDON - The world will have to spend an extra $500 billion to cut carbon emissions for each year it delays implementing a major assault on global warming, the International Energy Agency said on Tuesday.

At United Nations climate talks in Barcelona last week negotiators from developed countries said the world would need an extra six to 12 months to agree a legally binding, global deal to cut carbon emissions beyond a planned December deadline.

The IEA, energy adviser to 28 industrialized countries, said the world must act urgently to put greenhouse gases on a track to limit global warming to no more than 2 degrees Celsius.

Every year's delay beyond 2010 would add another $500 billion to the extra investment of $10,500 billion needed from 2010-2030 to curb carbon emissions, for example to improve energy efficiency and boost low-carbon renewable energy.

Much more needs to be done to get anywhere near an emissions path consistent with ... limiting the rise in global temperature to 2 degrees, said the IEA's 2009 World Energy Outlook. Countries attending the U.N. climate conference must not lose sight of this.

U.N. talks meant to agree a deal in Copenhagen in December to extend or replace the existing Kyoto Protocol have struggled to overcome a rich-poor rift on how to split the cost of curbing carbon emissions, for example from burning fossil fuels.

Developed countries accept that they have to take the burden of cutting carbon emissions, but want developing nations to accept binding actions too under a new treaty.

Poor countries want financial help to implement carbon emissions cuts and prepare for unavoidable global warming, including droughts, floods and rising seas.

The IEA report estimated that the world needed to invest an extra $197 billion annually by 2020 to make the necessary emissions cuts in developing countries, compared with a global total of $430 billion by then.

The Copenhagen conference will provide important pointers to the kind of energy future that awaits us, it said.

To continue present trends of energy demand and burning of fossil fuels would lead almost certainly to massive climatic change and irreparable damage to the planet, it said.

To implement swinging carbon cuts, on the other hand, would require a huge shift in the world's energy system.

That would raise, for example, the share of non-fossil fuels to 32 percent of total primary energy in 2030, from 19 percent in 2007. The share of the internal combustion engine in new car sales would fall to 40 percent by 2030 from more than 90 percent under current trends.