The world is facing a bill of $500 billion (£300 billion) for every year that it delays in reaching a global deal on climate change, the International Energy Agency (IEA) said yesterday.

Fatih Birol, chief economist with the IEA, told The Times that the annual cost of inaction — roughly equivalent to the annual GDP of Switzerland — would result from a steady build-up of additional concentrations of greenhouse gases in the atmosphere as the burning of fossil fuels accelerates.

“We need to make a major transition,” he said, speaking at the launch of the IEA’s 2009 World Energy Outlook in London. “But this will only happen if we get a global agreement as soon as possible.”

Last week, negotiators at United Nations climate talks in Barcelona conceded that the world would need another six to twelve months to reach a legally binding deal to curb greenhouse gas emissions, despite hopes that such a deal could be agreed next month at a meeting in Copenhagen.

Mr Birol said that every delay of a year beyond 2010 would add an extra $500 billion to the expected investment of $10.5 trillion required between 2010 and 2030 to cut emissions by building more low-carbon sources of renewable and nuclear power and reducing energy waste.

Nobuo Tanaka, executive director of the IEA, said that a deal at Copenhagen was vital, adding that all nations belonging to the Organisation for Economic Co-operation and Development (OECD) needed to commit to reductions to ensure a peak in global fossil fuel consumption before 2020.

“Governments must reach clear agreements to improve efficiency and develop alternative forms of energy, including nuclear, which do not emit so much greenhouse gas,” he said.

In the absence of a deal, the IEA said that global emissions of carbon dioxide from the burning of fossil fuels including oil, gas and coal were set to rise by almost 40 per cent by 2030, from 28.8 gigatonnes per year to 40.2 gigatonnes.

The IEA said that this rapid increase would trigger a rise in average global temperatures of about 6C (43F) by the end of the century — “with catastrophic consequences for our climate”.

The agency, the energy watchdog for the OECD, said that overall global energy demand was on track to increase by 40 per cent by 2030, with 90 per cent of this increase coming from emerging economies, especially China and India.

Coal is the fuel set for the biggest growth in consumption. Its use is expected to rise by 53 per cent to nearly seven billion tonnes per year by 2030. “Coal remains the backbone fuel of the power sector worldwide,” the IEA said.

The rise in the use of coal is expected to be followed by natural gas, where the IEA predicted growth in consumption of 42 per cent over the same time frame.

In recent weeks, the UN climate talks have stalled amid a deepening division between rich and poor nations as they struggle to agree to firm cuts in carbon dioxide emissions and how to allocate the burden of reducing energy use.

The IEA said that a deal in Copenhagen was critical to prevent an increase of no more than 2C (36F), which is considered an acceptable level of global warming.

Officials said that the worldwide economic downturn had actually triggered a 3 per cent fall in carbon emissions this year but that this trend was likely to reverse next year as economic growth returned.

The agency also pointed out that the financial crisis had led to a collapse in investment in the energy industry. It estimated that global investment in the oil and gas industry has fallen by 19 per cent or $90 billion this year compared with 2008.

“We think this is very risky when you look at the challenges ahead,” Mr Birol said.

He pointed out that by 2030 the world would need oil production equivalent to four times the output of Saudi Arabia in order to plug a yawning gap as production from existing fields is depleted.

Mr Birol said: “The fields which are producing today are going to significantly decline. We are very worried about these trends.”

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