That brought a new response from Ms. Nixon, who blasted Mr. Cuomo’s new energy-efficiency goals as “rehashed,” and criticized other elements of his environmental record, saying that polluters were “still being given free rein under the Cuomo administration.”
Mr. Cuomo’s campaign then responded by pointing out a range of his environmental accomplishments, including banning fracking in 2014, a plan to close down the Indian Point power plant, and a regional cap-and-trade program.
“We welcome anyone to this critical effort as we work to protect our environment for future generations and create a cleaner, greener New York,” said Abbey Fashouer, a spokeswoman for Mr. Cuomo’s campaign.
Administration officials also noted that several of Ms. Nixon’s proposals — including divestiture from fossil fuel companies and efforts to uphold the Paris Accord — have already been in the works under Governor Cuomo.
Since entering the race for governor a month ago, Ms. Nixon has been consistent and forceful in her criticism of the governor, saying he “governs like a Republican” and calling him “Andrew the bully,” a reference to his sometimes blunt political tactics.
With nearly five months until the September primary, polls have shown Mr. Cuomo, who is seeking his third term, with a commanding, but narrowing, lead in the polls.
Mr. Cuomo’s decision to ban fracking won wide praise, particularly among the progressive voters whom he has sometimes struggled to please — and whom Ms. Nixon is seeking to win over in her challenge from the left.
As a means to getting to 100 percent renewable energy, Ms. Nixon said her top priority as governor would be to pass the Climate and Community Protection Act, which calls for the state to transition to clean energy across all sectors, including transportation and buildings, by 2050. (The bill, which offers directives, goals and oversight, but little practical advice, has passed the Democrat-dominated Assembly, but died in the Republican-controlled Senate.)
It’s an idea touted by groups like Environmental Advocates of New York, whose executive director, Peter M. Iwanowicz, hailed Ms. Nixon for recognizing “that for New York to be considered a true climate leader, the state needs to have its goals in law not subject to the whims of the governor.”
Blair Horner, the executive director for the New York Public Interest Research Group, added the state was right to do something on a global issue that President Trump has expressed deep skepticism of.
“The planet is heating up, the experts say we have to stop burning fossil fuel, and New York has to be a leader,” Mr. Horner said. “Because Washington has checked out.”
Ms. Nixon also described climate change as a visceral danger — “This stuff is really scary,” she said — and as an economic and social issue, saying that poor neighborhoods often bore the brunt of the impacts of climate change.
“I’m an optimist at heart, but I’m also a realist,” she said. “And I know it’s going to get so much worse if we don’t act today.”