After a summer of climate-related flooding, droughts and heatwaves in parts of Europe, a new ranking by WWF reveals the continent's worst climate polluting power stations.

Dirty Thirty ranks the least efficient among the biggest carbon dioxide (CO2) emitters and finds that 27 of the 30 dirtiest power plants are coal-fired, with Agios Dimitrios in Greece, Frimmersdorf in Germany, and Aboño in Spain heading the WWF table.

The global conservation organization looked at the absolute CO2 emissions of power stations (million tonnes of CO2 per year) in 25 EU countries and ranked the 30 biggest emitters according to their level of efficiency (grams CO2 per Kilowatt hour).

Most of the Dirty Thirty are located in Germany (9 plants), followed by Poland (5 plants), Italy, Spain, and the UK (4 plants each). Greece has two lignite plants ranked in first and fourth place.

According to scientists, CO2 emissions are the main reason for global warming and devastating climate impacts on people and nature.

"The power sector is responsible for 37 per cent of all man-made CO2," said Imogen Zethoven, head of WWF's global PowerSwitch! campaign.

"Coal-fired power stations rank dirtiest, because they use the most CO2-intense fuel. To switch off global warming we have to replace them with cleaner alternatives, such as gas and renewables."

Imogen Zethoven: "The power sector is responsible for 37 per cent of all man-made CO2."

Germany is home to five of the ten dirtiest plants, and four of those are run by the country's power giant RWE, which is the biggest CO2 emitter in the European power sector, said the WWF.

The ranking showed that only half a dozen companies account for 19 of the 30 dirtiest power stations - besides RWE, these include Vattenfall (Sweden), Enel (Italy), Endesa (Spain), E.ON (Germany) and EDF (France).

Over the next 20 years many of Europe's worst polluting coal power plants will be decommissioned, says the WWF. This will provide a historic window of opportunity to cut CO2 pollution, the conservation group noted.

The Dirty Thirty replacement scenarios show that a switch to highly efficient gas in the decommissioned plants would slash CO2 emissions by 47.8 per cent by 2030. Replacing them with new coal plants would result in a mere 13.5 per cent reduction of CO2, nowhere near the deep cuts required. Replacing the old plants with renewable energy sources would result in a massive 73.4 per cent cut in CO2 emissions.

"A crucial part of the solution to CO2 emissions from power production is the European Emission Trading Scheme," said Zethoven.

"WWF is pushing for strong pollution limits and clear incentives to invest in wind, water and sun to be included in the second phase. Only tough limits on CO2 will force the utilities to replace dirty coal plants with cleaner gas or clean renewables."