The security of Parliament Hill was called into question Monday as 19 Greenpeace activists pulled off an audacious stunt that one senior Liberal senator called "hugely embarrassing" for the government.

The activists, wearing blue coveralls, climbing harnesses and hardhats, made it to the roofs of both West Block and Centre Block and unfurled protest banners in a high-wire demonstration designed to grab the attention of federal politicians on the opening day of the UN climate change summit in Copenhagen.

Colin Kenny, the Liberal chair of the Senate committee on national security and defence, said Monday it's a good thing the protesters were armed with climbing ropes and not rifles.

"We're very lucky it was just Greenpeace," he said. "If there were 19 people arriving with AK-47s, you could have a hell of a mess on your hands."

Kenny questioned whether there are enough security officers stationed at each building entrance and whether police could get to the Hill quickly enough if there were a serious incident.

He also noted Parliament's aging buildings are in a prolonged reconstruction period and wondered if additional steps need to be taken while renovations are under way.

Scaffolding currently hugs the west side of West Block and there is speculation protesters may have climbed it in order to access the roof.

"It would appear that no special precautions were taken for the scaffolding," he said.

Greenpeace spokeswoman Jessica Wilson said 19 activists arrived and were in place on top of the buildings between 7 and 7:30 a.m.

But she wouldn't say how they got there.

"In terms of the hows, that's not something we tend to talk about mostly because it distracts from the whys," she said.

"I appreciate the intrigue, but you can't always pull the curtain back on the magic show."

Police learned there were people on the roofs of the West Block and Centre Block at around 7:15 a.m., but couldn't say exactly how they got there.

"That's what being investigated right now to make sure appropriate actions are being taken by the RCMP and other security to make sure it doesn't happen again," said RCMP Cpl. Caroline Poulin.

In a Greenpeace video shot from the Centre Block roof, two RCMP officers appeared to stroll by the building without noticing anything amiss as the demonstrators prepared for their publicity stunt at about 7:30 a.m. The video also appeared to show a ladder against the Centre Block.

The first arrests came at about 8:20 a.m. after a banner was displayed on Centre Block that read, in French, "Stop the tarsands."

The drama at the West Block played out longer. Six protesters who rappelled down the building's face unfurled their banners on the Wellington Street side by about 9:15 a.m. The banners read: "Harper/Ignatieff: Climate inaction costs lives."

Within minutes, firefighters used a bucket truck to remove the banners and then picked up the six activists.

In addition to the 19 protesters who made it to the roof, one Greenpeace organizer was plucked off the sidewalk and taken into custody as well.

Ottawa police Const. Alain Boucher said the protesters -- who ranged in age from 20 to 63 -- were charged with mischief and could face fines or jail time, depending on whether they have criminal records. None were from the Ottawa area.

Boucher said city police were notified about the incident at 7:42 a.m. and had the first log entry at 7:45 a.m.

Wilson, the Greenpeace spokeswoman, watched the protest from the sidewalk on Wellington Street and explained it was carefully planned as part of the environmental group's countdown to Copenhagen.

"We think this is a necessary tactic when our government refuses to listen to the scientific community and its own citizens and acts instead in the interests of big oil," she said. "Sometimes you need to take it up a notch to get attention."

Wilson said Greenpeace wants countries, including Canada, to commit to hard targets for lowering greenhouse gas emissions to between 25 and 40 per cent below 1990 levels by 2020.

Politicians responded to the protest largely along party lines. While New Democrat MP Charlie Angus said it reflects the frustration many feel that the Harper government is "little more than a front for the tarsands," Conservative MP Laurie Hawn walked by and scoffed.

"It's nice to see we haven't lost our supply of morons in this country," he said.

Security on Parliament Hill is a mess of jurisdictions. The RCMP is the lead agency, but the Ottawa police handle any criminal investigations related to the Hill. Inside the buildings, security is handled by Senate and House of Commons security units.

The security breach is believed to be the first major one on Parliament Hill since 2003, when a man drove through a chain barrier in front of the Peace Tower in a vehicle carrying two gasoline containers.

The Monday protest happened only two months after Greenpeace demonstrators climbed Britain's Parliament buildings and remained there overnight.

Scotty Greenwood, executive director of the Canadian-American Business Council, who was attending an international trade conference on the hill Monday, said protesters would never be able to scale buildings in Washington, D.C.

"I really noticed the differences between Canadians and Americans as I came to the building this morning," she said.

"Here in Canada, I would just observe that there were ... lots of emergency personnel, fire trucks, paramedics, etc., there to make sure they were OK should something happen, ensure their safety. In our place it would have been snipers. No kidding."

Police have released the names of the 20 people arrested. At least five of those names come up in news archives as people involved in other high-profile protests and actions across the country. The oldest person on the Parliament roof Monday was 63-year-old June Kendall from Hudson, Que. The only previous news archive reference for a person of that name appeared nine years ago for a woman on the flower and vegetable show committee of the Hudson Garden Club.

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Previous Parliament breaches

Monday's incidents were not not the first security breaches in the parliamentary precinct. Past incidents include:

August 2003: A disgruntled Ottawa man rammed his car through a chain-link barrier and reached the steps of the Peace Tower before he was arrested. Two cans of gasoline were in the trunk.

April 1989: A gunman protesting the death of Lebanese civilians in Syria held passengers hostage on a Greyhound bus on the front lawn of Centre Block for several hours before surrendering.

May 1966: Paul Chartier

died in a washroom outside the Commons public gallery after a bomb he intended to throw into the chamber exploded in his hands prematurely.

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Have Your Say on the protest, just look for this story on our website ottawacitizen.com

Watch video footage shot by Scott Parker on Parliament Hill

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