(Corrects headline and lead to 'Western Europe's'. Moscow's Mercury City is taller.)
By Mark Anderson
LONDON, July 11 Greenpeace activists scaled Western Europe's tallest building in London on Thursday in a protest over plans by oil producer Royal Dutch Shell to carry out drilling in the Arctic circle.
The six women, who started their illegal climb in the early hours of the morning by climbing on the roof of London Bridge station, at the base of the building, hope to unfurl scenic posters of the Arctic within view of all of Shell's three London offices.
Ambulances waited below while the climbers posted live video of their ascent to Greenpeace's website. They face the possibility of being arrested after a gruelling 16-hour climb, Greenpeace spokeswoman Sara Ayech said.
"If we can get to the top of that skyscraper and do what we're planning then Shell's top executives will look out of their office windows and see the beauty of the Arctic towering above them," Victoria Henry, one of the climbers, said.
Greenpeace, which has long campaigned to seal off the Arctic from drilling, said the activists were carrying a "huge work of art" in their backpacks as they make their way up the building using safety ropes.
The newly built Shard stands 310 metres (1,017 ft) above the south bank of the River Thames, making it the tallest building in Western Europe.
A spokesperson for Shell said: "Recognising the right of individuals to express their point of view, we only ask that they do so with their safety and the safety of others in mind."
Shell canceled its 2013 Arctic offshore drill season after numerous troubles there last year. But it plans to send ships to study sites around oil prospects in the Chukchi and Beaufort seas, according to permit applications.
The Arctic may still hold 13 percent of the world's undiscovered oil and 30 percent of its gas.
"Shell is leading the oil companies' drive into the Arctic, investing billions in its Alaskan and Russian drilling programmes," Greenpeace said in a statement. (Reporting By Mark Anderson; Editing by Michael Roddy)