Justin Welby has hosted the Ecumenical Patriarch, sometimes known as "The Green Patriarch" as the Church meets to discuss what role it will play in the fight against climate change.
His All-Holiness Ecumenical Patriarch Bartholomew was introduced by the Archbishop of Canterbury as the man who "redefined" what it means to be a Christian leader.
The Ecumenical Patriarch has spent 24 years working with the environment and spoke strongly on the subject.
He stressed that clean air and clean water "should be available to everyone without discrimination."
He also told the audience, made up of bishops, faith leaders and MPs, that it is impossible to separate humanity and ecological conservation, saying the two are "forged together" and humans now will make the planet "ascent or descent."
His All-Holiness said that the current refugee crisis was a test of humanity and the way it treats the planet, saying the "world is overwhelmed by an unprecedented human crisis."
"Global warming is a moral crisis," he reiterated and economics, the environment, poverty and human rights are all inseparable.
He praised the last Century for the immense scientific progress that humans had made, but also lamented the immense destruction that had been caused.
"The choice is ours, our world is in deep crisis." The church has often reacted to matters rather than been at the forefront of change but he said humanity had an option; saying "never in history have human beings had so much opportunity to make such positive change."
He told the audience that interfaith discussions and solidarity were vital and that it is the responsibility of everybody to protect the planet for present and future generations: it is a "critical movement in history and the future of our planet."
His All-Holiness said that before people did not know that their actions were harming the planet for future generations, but now people can only pretend they do not know.
Speaking about the ties between religion and science he spoke passionately making clear it is an "ethical and honourable obligation" of church leaders.
"It's not too late to act, but we cannot afford to wait.
"Resources aren't limitless... we're all in this together."
Father John spoke on behalf of the Orthodox Church and repeated the Ecumenical Patriarch's approach of a multi-faith response.
Reference was made to Hindu, Muslim and Buddhist communities that are also holding talks and discussions on how they can each do their bit to slow down climate change.
He said it was easy to blame big corporations or politicians for climate change but that the time for this has passed and "collaboration is essential."
"Polluting creation is a sin.
"There's no simple way of resolving this crisis."
He told the audience that race, religion, culture and doctrine do not matter because every single person shares the "enjoyment and experience of our planet," and that Christians will be judged by the "tenderness" they show towards nature.
The conference also touched on the current refugee crisis and stressed the importance of the link between climate change causing famine or environmental degradation that leads to conflict or increased poverty and ultimately mass migration to other places.
Lake Chad was used as an example, a lake in Chad in central Africa.
Over a period of years it has been damaged by pollution and over fishing and surrounding countries like Sudan have drifted into conflicts as resources deplete and there is not enough water.
His All-Holiness concluded by saying that he has been preaching this message for the past three decades and that every human being has a right to a world "free of fantasists" and "free from pollution".
