Jeremy Faludi reports:
A common stereotype in the US is that Christians are conservative, and people who care about the environment are atheist liberals, or at least non-Christian. In fact, however, there are thousands of Christians worldwide, even socially conservative ones, who are concerned about saving the environment. There are dozens of faith-based environmental activism groups worldwide. Even if there weren’t, the impressive social leverage and organization of churches is not to be underestimated as a way to change the world, so it should receive more attention.
In the US, the larger regional/national organizations tend to be multi-faith (though most of their members are Christians, due to US demographics). Some, like National Religious Partnership for the Environment or Web of Creation, act as networks and clearinghouses of information, while others, like California Interfaith Power and Light are action-based and grassroots, helping members to perform energy audits of their churches and make efficiency improvements to their buildings, as well as educating.
There are many faith-specific organizations as well, such as the Evangelical Environmental Network (coiners of the phrase "What Would Jesus Drive?"), or the Lutheran Earthkeeping Network of the Synods; a good denomination-specific list can be found at Eco-Justice Ministries.