In what’s been described as a historic turning point, nearly 200 nations agreed in Paris Saturday to a global accord to rein in rising greenhouse gas emissions blamed for warming the planet. The accord was reached at the conclusion of the two-week U.N. climate change conference, known as COP21. Under the deal, nations will make voluntary commitments to begin cutting emissions. In addition, the deal provides billions more dollars to help poor nations cope with the transition to a greener economy powered by renewable energy. “What we saw in the last two weeks was that every country around the world agreed we have to do much, much more to fight climate change effectively, and to begin to set up a dialogue and mechanism for rich countries to aid the poor countries, and to make room for continuous ambition moving forward,” says Michael Brune, executive director of the Sierra Club and author of “Coming Clean: Breaking America’s Addiction to Oil and Coal.” But climate justice activists disagree on how effective the agreement will be in rolling back the effects of climate change. “What I see is an agreement with no timetables, no targets, with vague, wild aspirations,” says British journalist and author George Monbiot, columnist with The Guardian and author of the 2006 book, “Heat: How to Stop the Planet from Burning.” “I see a lot of backslapping, a lot of self-congratulation, and I see very little in terms of the actual substance that is required to avert climate breakdown.” We speak with both Brune and Monbiot about the agreement.