By Laura Barron-Lopez - 09/22/14 09:35 AM EDT
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 ClintonCould President Hillary heal a divided nation? Trump lands first major newspaper endorsement Clinton: Trump's election talk poses 'threat to our democracy' 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 WarrenSchilling lashes out: 'I'm apparently an anti-Semite' for asking questions Curt Schilling to Jake Tapper: How can Jews be Democrats? Small donors aren’t revolutionizing Congress. At least not yet. MORE (D-Mass.) or Bernie SandersBernie SandersCould President Hillary heal a divided nation? Clinton camp oppo research: Sanders has 'no accomplishments' Heck's rejection of Trump imperils Nevada Senate race 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.