By Richard Black
Environment correspondent, BBC News website
The IEA says governments must act fast - and protestors say they are not
The global recession provides a window of opportunity to curb climate change and build a low-carbon future, says the International Energy Agency (IEA).
It calculates that global greenhouse gas emissions will fall by 3% this year - an increase on previous estimates.
If governments take this opportunity to invest in clean technology, the global temperature rise can be kept below the G8 goal of 2C (3.6F), the agency says.
The findings were released at UN climate talks in Bangkok.
"The message is simple and stark: if the world continues on the basis of today's energy and climate policies, the consequences of climate change will be severe," said IEA executive director Nobuo Tanaka.
"Energy is at the heart of the problem - and so must form the core of the solution."
The recession is likely to mean emissions being 3% lower this year than last - and it will have a longer term impact, the IEA says, with emissions in 2020 projected to be 5% less than they would have been without an economic dip.
The biggest carbon cuts will come from improving energy efficiency, it says.
Slash, not burn
The agency presents a series of policy measures for different regions of the world and for countries at various stages of economic development.
Its prescription would lead to greenhouse gas concentrations being stabilised at the equivalent of 450 parts per million (ppm) of carbon dioxide - a level that, according to some analyses, offers a good chance that the rise in the global average temperature since pre-industrial times could be kept within 2C.
Without these policies, the agency calculates that concentrations will soar to 1,000ppm by mid-century - levels that, in many scientists' views, would lead to catastrophic and irreversible consequences.
But political and financial capital needs to be invested soon if the world is to follow the 450ppm path, it says, with emissions needing to peak around 2020.
The IEA sees carbon reductions coming mainly through higher efficiency
Developed countries, which it defines as those in the OECD and/or EU, will have to slash energy-related emissions by 17% in the next 11 years and by 50% by 2030.
Other major emitters such as China, India and Brazil would have to keep the rise in their emissions to 14% above current levels by 2030.
Countries in earlier stages of development would be able to increase their greenhouse gas output.
Globally, clean energy technologies would expand rapidly.
In the decade after 2020, the IEA's prescription includes a threefold expansion of nuclear power, a fourfold growth in the renewables sector and a 14-fold expansion of clean coal technologies.
The cost of this transformation would be $10 trillion between 2010 and 2030, the agency says - but improving energy efficiency would save virtually the same amount.
In a foreword to the report, Yvo de Boer, executive secretary of the UN climate convention (UNFCCC), warned that all of this was contingent on tying up an ambitious global deal during December's UN climate conference in Copenhagen.
"These results should motivate us all to step up efforts to reach an agreement with the requisite ambition," he said.
The IEA says low-carbon avenues would be explored for all walks of life
"The cost of addressing climate change is manageable. The cost of not doing so is unaffordable."
Mr de Boer is currently in Bangkok, chairing a preparatory meeting of officials from governments inside the UN convention.
On Monday, China and Sudan - which chairs the G77/China bloc of primarily developing nations - accused rich countries of trying to "kill off" one of the fundamentals of the Kyoto Protocol - that emission targets should be legally binding in some way.
They accuse western countries such as the US and Australia of wanting to make targets more flexible, which they fear will allow "wriggle room".
The IEA's analysis forms part of its annual World Energy Outlook, and has been released early in order that it can be discussed in the Bangkok talks.
Selected headline figures, including the recession's projected impact on emissions, were made public last month.