Churches in London are to be given advice on how to be more environmentally friendly.
The guide hopes to help churches reduce carbon emissions
"For Creed and Creation: A simple guidebook for running a greener church" has been launched by London's mayor.
It gives suggestions on everything from ways of reducing heating bills through to introducing car sharing schemes.
The Bishop of London, Dr Richard Chartres, said churches had a "pivotal role to play in tackling the stark reality of climate change".
The guide has been written by Dr Gillian Straine, who has a doctorate in climate science, and Nathan Oxley from consultancy Futerra.
Dr Staine has already been involved in running sustainability audits at a number of London's churches and the guide is designed to help all parishes understand and act on cutting their energy use.
Dr Chartres met mayor Ken Livingstone at City Hall on Wednesday to launch the guide.
He said: "London's churches reach out to hundreds of thousands of people every week and, according to the last census, 58% of the capital's population is Christian.
"We should be making our presence felt on the crucial issue of the environment."
Mr Livingstone said: "This green guide is a valuable tool for churches and their congregations to use to reduce their energy use.
"As a major world city what happens here can be an example that others follow."
The guide will be distributed free to over 4,000 churches in London.
It is hoped it will ultimately be adapted to encompass other religions and faiths, and be supported by a telephone advice line.