ALBANY — In her first major environmental proposal, Cynthia Nixon, who is challenging Gov. Andrew M. Cuomo for the Democratic nomination, called on New York State to commit to 100 percent renewable energy sources by 2050, a benchmark that has been something of a Holy Grail for activists concerned about the warming of the planet as a result of the burning of fossil fuels.

Her announcement on Friday came just hours after the governor’s office had issued its own call for increased efficiency targets to right “the devastating effects of climate change.” Both moves seemed calculated to coincide with Earth Day on Sunday, but also as a means of upstaging the other’s initiatives.

Ms. Nixon called for a complete embrace of renewable energy, like that produced by wind, water or solar. Mr. Cuomo has, to this point, committed to 50 percent renewable energy by 2030.

Speaking to a crowd in Rockaway Beach, Queens, which was badly damaged by Hurricane Sandy in 2012, Ms. Nixon said that action to prevent climate change “can’t fall victim to business as usual in Albany and a political system that caters to the needs of corporate donors over the future of New York’s children.”