VANCOUVER — Greenpeace celebrated its 40th anniversary in Vancouver on Thursday, with the environmental group praising the Canadian city's role in spawning a global movement at the forefront of green activism.

It was from Vancouver that a boat named "Greenpeace" set off on September 15, 1971 for Amchitka Island, Alaska, to protest American nuclear testing. The US Coast Guard blocked it, but the campaign helped end the atomic tests in 1972.

Young sunburned activists in jeans joined the remaining and increasingly elderly Greenpeace founders, many still sporting the long hair of Vancouver's counter-culture hippie days, in the Canadian city to mark the anniversary.

"They said by putting our lives and bodies on the line, we can make a difference," Greenpeace International director Kumi Naidoo said to loud applause, noting that their example had inspired millions.

City officials planted a yellow cedar tree and proclaimed the environmental group's birthday "Vancouver Greenpeace Day."

"Greenpeace literally changed the world," said Mayor Gregor Robertson, citing its campaigns to end nuclear tests, oppose whaling, protect oceans and natural habitats, preserve the Antarctic, and end use of drift nets for high-seas fishing.

Naidoo praised Vancouver, known as a green city for its relatively low carbon output, for officially recognizing the organization -- but sharply criticized Canada's recent environmental record.

For its opposition to global measures to reduce climate change, and support of Alberta's oil sands development, Canada "is on the wrong side of history," he said, describing the federal government's positions as "pathetic."

Although Greenpeace was founded in Vancouver -- partly by Americans who moved here to oppose the war in Vietnam -- the organization quickly outgrew the city, with its international headquarters now in Amsterdam and with offices worldwide.