Long-time environmentalist and spiritual leader to the world's Orthodox Christians, Bartholomeos I, has urged attendees at the world's largest ecumenical conference to repent and change their lifestyle in response to threats posed by climate change.

Bartholomeos, known as the "Green Patriarch", warned more than 2,500 European Christian leaders on the threat of climate change to the survival of humanity and the need to respond immediately.

"There is no time for waiting or delay. Otherwise, we are willingly and irresponsibly, even dangerously, shutting our eyes," said Bartholomeos at the Third European Ecumenical Assembly in Sibiu, Romania, on Wednesday, according to Ecumenical News International.

"What must immediately take place is repentance, together with the change of life that accompanies repentance," he said.

The Orthodox patriarch was one of a number of speakers at the six-day ecumenical assembly organised by the Conference of European Churches and the Council of European (Roman Catholic) Bishops' Conferences (CCEE).

The Sept 4-9 assembly seeks to create stronger Christian unity across Christian traditions in Europe, bringing together the continent's Roman Catholic, Protestant, Anglican, and Orthodox churches.

During his talk, Bartholomeos chastised humans for "shamelessly" abusing God's creation.

"We are concerned about God's creation, which is constantly and shamelessly rendered the object of abuse," the ecumenical church leader said. "We are concerned about the elementary climate and other conditions - quite literally, about the air and the oxygen breathed by modern man and which future generation, as we fear will seek in vain.

"We are, finally, concerned about humanity's mere survival on this continent and our planet," he said.

From Sibiu, Bartholomeos is scheduled to travel to an interfaith symposium in the Arctic Circle to highlight the environmental damage face by the region's ecosystem.

Other notable figures at the Sibiu meeting include Cardinal Walter Kasper, the president of the Pontifical Council for Christian Unity; Metropolitan Kirll of Smolensk, the chief ecumenical officer of the Russian Orthodox Church; the Rev Samuel Kobia, the general secretary of the World Council of Churches; and the Bishop of London, the Rt Rev Richard Chartres.