* EU close to meeting 2020 carbon goals already
* Commission expected to proposed 2030 targets around year-end
* U.N. climate deal expected in 2015
* Environmentalists say cost is false debate, want efficiency goal
BRUSSELS, Oct 24 (Reuters) - The European Union needs to cut greenhouse gas emissions by 50 percent from 1990 levels by 2030 to avoid the worst effects of climate change, according to a British government paper, likely to fuel debate on whether deeper cuts are affordable.
Energy costs have shot up the political agenda across Europe, where power prices are around double those in the United States.
Some EU states and industry have blamed green energy subsidies for stoking prices and say competitiveness is a more pressing concern in fragile economic times than emissions cuts.
The European Commission, the EU executive, is expected to unveil proposed 2030 green energy goals around the end of this year.
"The EU needs to be prepared to offer an international greenhouse gas mitigation target of 50 percent reduction on 1990 emissions," the British paper, seen by Reuters, says on the EU 2030 targets.
No one from Britain's Department of Energy and Climate Change was immediately available to comment.
The paper refers to scientific modelling on how to cap global warming at 2 degrees Celsius, the limit scientists say would prevent the most devastating effects of climate change.
EU sources have said the Commission is looking at a 40 percent cut in domestic greenhouse gases versus 1990 levels by 2030. It could be supplemented by up to 10 percent more cuts achieved by buying CO2 credits on the international market.
Britain itself has committed to deep emissions cuts to reach a goal of an 80 percent reduction by 2050.
As a whole, the European Union has already nearly met a target to cut 1990-level emissions by 20 percent by 2020, as a result of lower energy demand following recession and a shift towards green power, such as solar and wind.
But Poland, for instance, which is heavily reliant on carbon-intensive coal, has sought to make any further EU promises conditional on the rest of the world pledging to do more. Next month, it hosts U.N. climate change talks in Warsaw as a step towards a new global deal in 2015.
Existing 2020 goals to cut carbon emissions by 20 percent compared with 1990 levels, increase renewable energy use to 20 percent and to achieve energy savings of 20 percent were agreed before the economic crisis struck.
For 2030, the Commission is expected to propose only two targets - one on emissions and one on renewable power.
While keen on lowering emissions, with the help of nuclear power, Britain does not want a renewable energy goal. Germany, which is working on its Energiewende, or shift from nuclear towards renewable power, does.
Political will on a 2030 efficiency target is all but non-existent because member states are unwilling to invest in the necessary steps, such as better building insulation.
Environmentalists say that is a huge error when increased efficiency would solve all the European Union's problems by cutting fuel bills, lowering emissions and curbing dependency on imported oil and gas. ($1 = 0.7256 euros)
(Additional reporting by Nina Chestney in London; Editing by Susan Fenton)