Activists briefly blocked traffic outside Helsinki's parliament and protested in Espoo, the seat of Fortum, the Finnish energy group whose subsidiary Uniper runs the Datteln IV power plant in Germany's western state of North Rhine-Westphalia (NRW).
In parallel acts Friday, Germany's BUND branch of Friends of the Earth handed over a 41,500-person petition to the Finnish embassy in Berlin, while alongside the plant itself protesters in canoes paddled the adjacent Dortmund-Ems canal.
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The petition called on Finnish Prime Minister Sanna Marin to quickly decommission the plant, which only went online in May. BUND's Antje von Broock describing Datteln as "superfluous," given Germany and Finland's policies on climate warming.
Chancellor Angela Merkel's government, currently holding the EU's rotating presidency, began its term in July on vows to make climate policy its central focus.
Despite recent booms in renewable energy sources such as wind and solar power generation, coal still covers about a quarter of Germany's energy usage.
The federal and regional NRW governments argue that Datteln's combustion efficiency enables the decommissioning of older plants as part of Berlin's plan to exit coal-generated power by 2038.
That scenario includes major financial compensation for traditional brown and stone-coal extraction regions in Germany's east and west.
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'Not soon enough'
Critics argue this plan should apply far earlier, with BUND's director in NRW Dirk Jansen on Friday urging intervention by German rail operator Deutsche Bahn.
"Datteln 4 currently produces its electricity almost exclusively for Deutsche Bahn," Jansen said.
"If the railways were to stop consumption of the dirty coal-fired power, this could mean the end of the power plant responsible for excessive energy supply.''
On Friday, federal government spokesman Steffen Seibert said Merkel would hold "informal" talks next Thursday in Berlin with young climate activists, including Sweden's Greta Thunberg and Germany Luisa Neubauer.
Both are leading figures in the Fridays for Future movement.
ipj/mm (epd, AFP, dpa)