The former Archbishop of Canterbury, Dr Rowan Williams, led prayers at a climate change protest in front of the Houses of Parliament on Wednesday.
Dr Williams, Chair of Christian Aid, said people needed to be "truthful" about the consequences of their own actions and "act courageously" in order to limit the harm caused by climate change.
"It's clear that the impact of climate change on the poorest people in the world drives instability, injustice and conflict," he said.
He added: "We need the churches, we need our political leaders, we need civil society, we need our own hearts to be touched.
"If we are to respond effectively to the challenges of our world, we need to respond with our spirits cleared and our action open, courageous and lucid."
Hannah Abban, a member of Christian Aid's Prophetic Activists scheme, said it was important that everyone see themselves as part of the solution.
"Climate change is a human problem," the 23-year-old said.
"Even as an activist, as I speak to you all today I stand here with privilege. I don't go outside and see my crops have failed. I don't live in a low-lying country where citizens live in perpetual fear.
"We can technically go on the way we are living in, wastefully and in luxury without having to fear immediate repercussions.
"It's important for us to educate ourselves on the problem at hand but also to explore solutions and what part we can play within the bigger picture."
The vigil marked the launch today of a nationwide prayer chain across the UK for tougher action on climate change ahead of the COP26 summit taking place in Glasgow later this year.
Among those present at the vigil were bishops from the Diocese of Southwark and MP David Lammy.
Individuals and churches can sign up to be a part of the prayer chain at caid.org.uk/prayerchain.
