Rep. Alexandria Ocasio-Cortez (D., N.Y.) said Wednesday that Miami has only a few years left on this planet.

At an NAACP forum, the democratic socialist touted the Green New Deal, her radical climate change plan many have criticized as unrealistic. Economists, investors, and energy industry experts have frequently noted the plan's astronomical costs and the unreliability of renewable energy, but Ocasio-Cortez said her critics are the ones who are "not realistic."

"When it comes to climate change, what is not realistic is not responding … with a solution on the scale of the crisis—because what's not realistic is Miami not existing in a few years," she said to applause.

"We need to be realistic about the problem," she added.

Ocasio-Cortez proposed the Green New Deal as an "aspirational" plan and even resisted Republicans' desire to vote on it, but fellow democratic socialist Sen. Bernie Sanders (I., Vt.) released a fleshed-out version of the plan as part of his presidential platform. Sanders's plan would cost $16 trillion—more than 20 times as expensive, adjusted for inflation, as Franklin Roosevelt's New Deal.

Sen. Kamala Harris (D., Calif.) has also made the Green New Deal part of her presidential platform, saying she will end the filibuster and "do whatever is necessary" to pass the plan.

The plan has received plenty of pushback, even from those who want government intervention to stop climate change. Writing in the Wall Street Journal, Greg Ip said the government must take action on climate change but the Green New Deal's provisions "seem engineered to be as expensive as possible."

Ocasio-Cortez has welcomed opposition from leaders in the energy industry, which she blames for pollution and climate change. They have argued the specifics of her plan are unrealistic.

"I think one of the reasons why you're not hearing a lot about it is because it's so unrealistic," Mike Sommers, the president of the American Petroleum Institute, told CNBC.

"When talking about the Green New Deal, I think for most of our members, yes, they take it seriously from a public relations perspective, but you look at what it actually means, and more than anything, it's a plan to have a plan right now," Sommers added.