It will not cool the globe, but the new world climate accord may temper Washington's political heat for Barack Obama and it has crucially given him a deal he can defend at home.

The US president engineered the compromise with rising powers China, Brazil, South Africa and India, at the tense UN climate summit in Copenhagen.

"For the first time in history all major economies have come together to accept their responsibility to take action to confront the threat of climate change," Obama said, putting the best possible spin on an agreement that many said fell short of the summit goals and what science demands to stem global warming.

An obvious flaw: the pact is not legally binding, and while it commits to limit warming to two degrees Celsius, it fails to set targets for greenhouse gas emissions cuts.

But that very omission may make the accord palatable in Washington, where climate change scepticism is rising and critics warn Obama's energy revolution could squelch frail economic growth.

Obama came to Denmark under pressure to make concessions to Europe and developing states - but stuck by his offer to only cut US greenhouse gas emissions by 17 per cent from 2005 levels by 2020.

He also dodged saying how much the US would pay as part of a deal to help developing states tackle warming.

Holding that line may help preserve fragile support for a deal in the US Senate.

Copenhagen was another lesson for Obama in the application, and limits of US power.

He has smashed records for travel by a first-year president, but Obama has few foreign policy triumphs. Iran has spurned his hand of engagement, the Afghan war got worse, and his Middle East peace drive is stalled.

Domestic foes brand him a soft touch on the world stage and mock his failure in Copenhagen to win the 2016 Olympics for Chicago.

So going home empty-handed would have been another devastating blow, and Obama's dwindling approval ratings may benefit from accounts painting him as a diplomatic maestro behind the accord.

Copenhagen Accord

US President Barack Obama reached a climate agreement last Friday with India, South Africa, China and Brazil. The deal outlined fell far short of the ambitions for the Copenhagen summit.

Here are key points from the agreement, which is titled 'Copenhagen Accord'.

Long-term goals

'Deep cuts in global emissions are required according to science... with a view to reduce global emissions so as to hold the increase in global temperature below 2 degrees Celsius.'

Legally binding deal?

A reference in an earlier draft to adopt a legally binding climate agreement by next year was missing in the final draft. This upset the EU and some other nations, such as the Pacific island country of Tuvalu, which fears being swamped by rising sea levels.

Emissions reduction

Details of mitigation plans are included in two separate annexes, one for developed country targets and one for the voluntary pledges of major developing countries.

These are not binding, and describe the current status of pledges - ranging from 'under consideration' for the US to 'Adopted by legislation' for the EU.

Verification

A sticking point for a deal, largely because China refused to accept international controls, the section on monitoring developing nation pledges is one of the longest.

It says emerging economies must monitor their efforts and report the results to the UN every two years, with some international checks to meet Western transparency concerns but 'to ensure that national sovereignty is respected'.

Financing for poor nations

The text says: 'Developed countries shall provide adequate, predictable and sustainable financial resources, technology and capacity-building to support the implementation of adaptation action in developing countries.'

It mentions as particularly vulnerable and in need of help the least developed countries, small island developing states and Africa.

'Developed countries set a goal of mobilising jointly $100 billion a year by 2020 to address the needs of developing countries. The funds will come from a wide variety of sources, public and private, bilateral and multilateral.'

An annex carries the following short-term financing pledges from developed countries for 2010-2012:

EU - $10.6 billion
Japan - $11 billion
US - $3.6 billion

Forest protection

The accord 'recognises the importance of reducing emissions from deforestation and forest degradation and the need to enhance removals or greenhouse gas emission by forests', and agrees to provide 'positive incentives' to fund such action with finance from the developed world.

Carbon markets

Mentioned, but not in detail. The accord says: 'We decide to pursue various approaches, including opportunities to use markets to enhance the cost-effectiveness of and to promote mitigations actions.'