In an open letter to The Times, Christian Aid and CAFOD said world leaders must "act before it's too late" on the issue.
The COP21 conference in Paris begins on Monday 30th and ends on December 11th. 196 countries are attending the event, and climate activists are hoping they will be able to reach a legally binding deal to lower carbon emissions to a necessary level.
That deal will be met with varying levels of resistance from the different countries represented, depending on the amount of money they have invested in energies and practices which damage the environment, and the amount they are currently experiencing the affects of climate change such as flooding or drought.
It is also hoped countries will be able to change their business methods, for example the way they make things and farm, to more sustainable options.
Coal will be under particular scrutiny, as it is widely seen as the most CO2-emitting fuel in use. Some countries still rely very heavily on coal.
Both the Anglican and Catholic Churches have been particularly outspoken on climate change. Pope Francis released an encyclical - the highest level of teaching a pontiff can issue - specifically on the environment earlier this year.
The open letter said: "Thousands of people will march in London today and in cities around the world this weekend, calling for action to tackle climate change.
At the talks in Paris, our leaders must confront the ecological destruction, poverty and injustice that climate pollution carries in its wake, and act before it is too late.
"We believe that hope lies in acting together to address the shared problems faced by humanity."
