Hot air is troubling yet another round of UN climate talks, but this time, in Doha, it is in the guise of carbon credits that some countries wish to bank, rather than the usual diplomatic bluster.

"Hot air" is the name given to Earth-warming greenhouse gas emission quotas that countries were given under the first leg of the 1997 Kyoto Protocol and did not use -- some 13 billion tonnes in total.

The credits can be sold to nations battling to meet their own quotas, meaning that greenhouse gas levels decrease on paper but not in the atmosphere.

Poland and Russia emitted much less than their lenient limits, and are insisting in Doha on being allowed to bank the difference beyond 2012 -- a move vehemently opposed by most other parties.

"There is enough hot air in the process... we do not need any more!" said Seychelles climate negotiator Ronny Jumeau on behalf of the Alliance of Small Island States at high risk of global warming-induced sea level rise.

Agreement on hot air is key to the Doha delegates extending the life of the Kyoto pact, whose first leg expires on December 31.

"I am afraid this will remain a major issue right until the end" of the discussions in the Qatari capital, which are supposed to end in a deal by Friday, said French climate ambassador Serge Le Peletier.

The Kyoto Protocol is the world's only binding pact on curbing greenhouse gases, but locks in only developed nations and excludes major developing polluters such as China and India, as well as the US which refused to ratify it.

The annual UN climate huddle seeks to extend Kyoto into a "second commitment period" for developed countries leading up to a new, universal pact for all the world's nations that must enter into force in 2020.

The United Nations is targeting a manageable global warming limit of two degrees Celsius (3.6 F) on pre-industrial levels, but science shows that Earth may be heading for double that.

To achieve 2C, scientists say emissions must fall to less than 35 billion tonnes per year in 2030, but a report this week said levels are likely to plateau at around 50 billion tonnes in the coming decades, probably higher.

Under Kyoto, industrialised nations were given assigned amount units (AAUs) which each correspond to a tonne of CO2 equivalent -- a measure of greenhouse gas.

Former East Bloc countries were given high quotas in exchange for joining the protocol and to compensate for the fact that burning fossil fuels, including at coal-fired power stations, was key to their economic development.

Poland emitted 800 million tonnes fewer than its quota and Russia, which will not take on a binding commitment under the Kyoto follow-up, 5.8 billion tonnes.

Most parties in Doha, particularly countries most at risk of warming-induced droughts, floods, rising seas and storms, insist that the excess be dropped or at least reduced post-2012.

But the European Union says retaining the credits would have no practical effect, as EU legislation does not allow them to be counted towards the bloc's target of reducing emissions by 20 percent from 1990 levels by 2020.

Australia, the second major carbon market, has a similar stance.

Climate analyst Alden Meyer of the US-based Union of Concerned Scientists, however, believes Poland and Russia may be taking a longer-term, post-2020 view.

"I think they both would like to be able to carry those credits forward... into whatever new agreement is negotiated," he told AFP.

"They either want to be able to use those credits to meet any obligations they negotiate under that long-term deal, or to sell them in the market."

Emmanuel Guerin, of France's Institute for Sustainable Development and International Relations, said the credits may be much more valuable in the future.

According to NGO group Carbon Market Watch, the AAU price has dropped from 13 euros ($17) in 2008 to less than 50 cents this year because of over-supply.

"They (Poland and Russia) believe that in future, other countries that take on more serious engagements may need the credits, and that they will be worth more," said Guerin.

Asked this week about Russia's post-2020 AAU plans, climate envoy Alexander Breditsky said: "We are not there yet."