The future may be renewable, but evidence of ancient civilizations isn't always reparable.

"Time for Change; The Future is Renewable" was the message of Greenpeace activists protesting at the ancient Nazca Lines UNESCO World Heritage Site in the Peruvian desert on Monday.

The activists placed yellow letters next to a famous hummingbird design, and now Peruvian authorities are threatening to sue Greenpeace and criminally charge the activists with "attacking archaeological monuments," according to The Associated Press

The demonstration was timed to coincide with United Nations' Lima Climate Change Conference ending Friday.

"It's a true slap in the face at everything Peruvians consider sacred," Deputy Culture Minister Luis Jaime Castillo told The Associated Press of the activists' decision to enter a "strictly prohibited" area next to a famous hummingbird design.

"You walk there, and the footprint is going to last hundreds or thousands of years," Castillo told the AP. "And the line that they have destroyed is the most visible and most recognized of all."

Located about 400 kilometers south of Lima and covering about 450 square kilometers, the Lines and Geoglyphs of Nasca and Pampas de Jumana World Heritage Site has geoglyphs and lines dating from 500 B.C. through A.D. 500.

Artwork that is made from placing or moving stones, earth or other objects, geoglyphs in the area fall into two general categories, according to the site's UNESCO listing. One type is representational, featuring animals, plant life and other extraordinary figures. The other consists of the lines, mostly straight lines crossing the region's pampas in different directions. Some are long -- several kilometers -- and form shapes. The designs are believed to have had ritual astronomical functions.

Greenpeace has apologized for the action. "Without reservation Greenpeace apologises to the people of Peru for the offence caused by our recent activity laying a message of hope at the site of the historic Nazca Lines," the organization said in a statement . "We are deeply sorry for this.

"Rather than relay an urgent message of hope and possibility to the leaders gathering at the Lima UN climate talks, we came across as careless and crass."

Greenspace says it has met with the government to apologize and will cooperate with any investigation and face "reasonable and fair consequences."

The group says its international executive director, Kumi Naidoo, is in Lima this week to personally apologize and to participate in discussions with the Peruvian authorities.