Bill Nye is done being the nice guy.

While discussing climate change on Sunday's "Last Week Tonight With John Oliver," the famous "Science Guy" didn't hold back on the state of the Earth.

"The planet's on (expletive) fire," Nye said, point-blank.

Oliver invited the science educator on his HBO show after wading through the Alexandria Ocasio-Cortez-backed Green New Deal, which calls for shifting completely from fossil fuels to renewable energy in the coming years and prescribes a broad platform that includes free housing, medical coverage and higher education for all Americans.

Citing a study that warned of food shortages and wildfires as soon as 2040, Oliver brought on Nye to de-mystify carbon pricing, an economist-backed method of reducing global warming by charging those who emit carbon dioxide.

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But Nye wasn't feeling as jovial as usual.

"By the end of this century, if emissions keep rising, the average temperature on Earth could go up another four to eight degrees. What I'm saying is the planet's on (expletive) fire," said Nye, actually setting fire to a globe.

"There are a lot of things we could do to put it out – are any of them free? No, of course not. Nothing's free, you idiots. Grow the (expletive) up. You're not children anymore. I didn't mind explaining photosynthesis to you when you were 12. But you're adults now, and this is an actual crisis, got it? Safety glasses off, (expletives)," Nye said, attempting to blow out the fire on display.

"I think we've all broken Bill Nye," declared Oliver.