Sunday on Twitter, Swedish teenage climate change activist Greta Thunberg slammed U.S. climate envoy John Kerry over his recent comments regarding climate change.

“I am told by scientists, not by anybody in politics but by scientists, that 50% of the reductions we have to make to get to net zero by 2050 or 2045, as soon as we can, 50 percent of those reductions are going to come from technologies that we don’t yet have,” Kerry told the BBC on Sunday. “That’s just a reality. And people who are realistic about this understand that’s part of the challenge.”

Thunberg responded by firing off a sarcastic tweet: “Great news! I spoke to Harry Potter and he said he will team up with Gandalf, Sherlock Holmes & The Avengers and get started right away!”

Last month on MSNBC’s Mehdi Hasan Show, Thunberg complained about Biden’s inadequate climate change policies. Asked how she would grade Biden so far on climate change, she replied, “I’m just a teenager, so I don’t have the mandate to sort of give grades like that. My opinions on this doesn’t matter​. You should rather look at the science and whether his policies are in line with the Paris agreements and to stay below 1.5 or even 2 degrees Celsius, and then you can clearly see that, no, it’s not nearly enough in line with the science. That’s not me saying, that’s just black and white, looking at the facts​.”

She went on to complain that the Biden administration is not treating climate change as an “existential threat”: “They are just treating the climate crisis​ ​as it was a political topic, among other topics. Treat it as a crisis, that’s the Number one step​ we need to do.”

When you’ve lost Greta Thunberg, you’re in danger of losing her generation of voters. Better hurry up and save the planet, Democrats!