A number of climate activists who rallied on Sunday in New York City for the largest climate change march to date, said they aren't convinced Hillary ClintonHillary Rodham ClintonFeehery: A March without purpose The Women's March was about tantrums, not women Of biscuits and footballs: The perils of presidents and the nuclear codes MORE is their candidate if she runs for president.
Founder of the prominent activist group 350.org, Bill McKibben, told MSNBC that the former secretary of State has a lot to prove.
“I think Hillary Clinton has an awful lot to demonstrate to environmentalists and people who care about climate change,” said McKibben, whose group helped organize Sunday's march.
“She oversaw the complete fiasco that was the Copenhagen Conference as secretary of State. That was the biggest foreign policy failure since Munich. It’s not a proud record," he added.
In a recent renewable energy speech in Las Vegas, however, a majority of Clinton's speech was dedicated to sounding the alarm on climate change.
In her book, "Hard Choices," the likely democratic front-runner in 2016, made the 2009 Copenhagen meeting the focus of one of the chapters, touting her work with President Obama to get critical conversations flowing between the U.S. and China.
Still, actor Mark Ruffalo isn't sure Clinton will get support from greens, a critical faction of the base that has helped Obama.
Clinton's problem is her stance on fracking for natural gas, a significant element of the U.S. energy boom, which Obama supports as well.
"Unless she changes that, the climate change voters, the people who take this very seriously, are not going to be able to get behind her,” Ruffalo told MSNBC.
“If someone can offer up another way forward, [climate voters] are going to get behind that person. Just like Obama, they got behind him,” Ruffalo added, suggesting Sens. Elizabeth WarrenElizabeth WarrenAT&T beefs up lobbying after merger proposal Sanders: I'll work with Trump on trade Poll: Warren could face rocky reelection path MORE (D-Mass.) or Bernie SandersBernie SandersThe Rockefeller scheme to attack Exxon Mobil AT&T beefs up lobbying after merger proposal HELP Committee won't hold second hearing for DeVos MORE (I-Vt.) as possible alternatives, according to MSNBC.
“These are people who get this, who are not beholden to this 100-year-old fossil fuel stranglehold on leaders like Hillary Clinton," Ruffalo said.