The global climate movement has grown dramatic momentum in the last few years — hundreds of thousands of citizens around the world took to the streets to call for bold climate action in 2014, Pope Francis dedicated his papal encyclical to the care of our common home, and a record number of leaders came together in Paris to adopt a historic international agreement on climate change.

And yet, warns John Schwartz for The New York Times, “the movement that started with a straightforward mission — to get more people to appreciate the dangers of climate change as a precursor to action — is feeling growing pains. What may seem like a unified front has pronounced schisms, with conflicting opinions on many issues, including nuclear power and natural gas, that are complicating what it means to be an environmentalist in this day and age.”

Some of the most contentious issues at play here are the safety or potential risks of nuclear power, the politically contentious issue of natural gas and fracking, the value of interaction with fossil fuel companies, and insiders versus outsiders in the environmental movement.