In a rejoinder to President Trump, 16-year-old climate activist Greta Thunberg on Tuesday embraced a sarcastic description of herself by the president that followed her impassioned — and somewhat fatalistic — plea to global leaders at the United Nations.

Trump had responded to Thunberg’s appearance Monday at the U.N. climate summit with a late-night tweet, mocking her pessimistic tone earlier in the day.

“She seems like a very happy young girl looking forward to a bright and wonderful future. So nice to see!” Trump said on Twitter shortly after 11:30 p.m. Monday.

He attached a news account of Thunberg’s remarks to the gathering in New York that highlighted a dire quote: “People are suffering, people are dying, entire ecosystems are collapsing. We are in the beginning of a mass extinction, and all you can talk about is money and fairy tales of eternal economic growth.”

News cameras captured climate activist Greta Thunberg staring at President Trump as he walked by her at the U.N. climate summit on Sept. 24. (AP)

On Tuesday, Thunberg altered her Twitter profile, describing herself to her 1.9 million followers as “a very happy young girl looking forward to a bright and wonderful future.”

In her panel appearance on Monday, Thunberg chastised leaders for praising young activists like herself while failing to deliver on drastic actions needed to avert the worst effects of climate change, and she warned that if the world continued with business as usual, her generation would face an insurmountable catastrophe.

“This is all wrong,” a visibly emotional Thunberg, her face flushed and tears in her eyes, said in her speech.

Cameras caught Thunberg giving Trump an icy stare as he arrived at the U.N. gathering earlier in the day.

Trump, who in the past has called climate change a “hoax,” gave scant attention to the issue that dominated the day on Monday.

After scheduling one of his administration’s marquee events — a forum on religious freedom — during the U.N. climate summit on Monday, he dropped by the climate event for 14 minutes in a surprise visit. He did not speak and left after listening to remarks from Indian Prime Minister Narendra Modi and Angela Merkel, the outgoing German chancellor.

Merkel and French President Emmanuel Macron offered far different reactions on Monday to Thunberg, who began skipping school in her native Sweden a year ago to protest inaction on climate change.

Merkel met with Thunberg and posted a photo of her impromptu summit with the young activist.

Macron appeared to respond to Thunberg less than an hour later when he addressed the gathering in French and called on his fellow leaders to take more ambitious action given the urgency of the climate threat

“We’ve seen the emotion this morning,” Macron said. “We cannot let our youth spend every Friday demonstrating for the climate and simply answer, ‘Everything is fine, we are doing everything right.’ We are still far from the account.”

Rep. Eric Swalwell (Calif.), a former Democratic presidential candidate, reacted to Trump’s tweet about Thunberg with one of his own early Tuesday morning.

“By rallying the world to save itself, she’d already make a better @POTUS than you,” he wrote, adding: “(Also, she’s not a liar, a crook, or a whiny toddler.)”

Juliet Eilperin and Seung Min Kim contributed to this report.