Stephanie Keith/Getty Greta Thunberg
Teenage climate activist Greta Thunberg told U.S. lawmakers on Thursday morning to "use your common sense" and take action to limit and ultimately eliminate the country's fossil-fuel emissions.
"I'm not even going to explain why we need to make real drastic changes and dramatically lower our emissions in line with the overall current, best available science," Thunberg, 18, said while testifying during a virtual congressional hearing on the climate.
"It is the year 2021," continued the former TIME Person of the Year, who built an international profile with her blunt warnings on the issue. "The fact that we are still having this discussion — and even more that we are still subsidizing fossil fuels directly or indirectly using taxpayer money — is a disgrace."
Thunberg's virtual appearance on Capitol Hill comes the same day that President Joe Biden welcomed global and national leaders for the first "Leaders Summit on Climate," taking place Thursday and Friday.
Politicians like Canadian Prime Minister Justin Trudeau, German Chancellor Angela Merkel and New Zealand Prime Minister Jacinda Ardern were among the virtual attendees, along with Russian President Vladimir Putin (despite tensions with Biden) and Brazilian President Jair Bolsonaro, and Chinese President Xi Jinping.
"No nation can solve this crisis on our own, as I know you all fully understand," Biden, 78, told his counterparts at the summit. "All of us, all of us — and particularly those of us who represent the world's largest economies — we have to step up."
Biden laid out a plan, he said, to be a net-zero emissions economy by 2050 — though he implored other countries to follow suit, noting the U.S. makes up only 15 percent of the world's emissions. (It's still the largest emitter worldwide.)
Thunberg, who has been famously direct in her criticism of what she calls hesitancy to embrace the science and risks of climate change, told lawmakers in her testimony she was not holding her breath on such promises.
"I don't believe for a second that you will actually do this," she said.
Drew Angerer/Getty Greta Thunberg
She laid out what she says major world powers like the U.S. need to do to start relieving the world of the dangerous effects of climate change. Those critical of her calls for reform say the changes would too seriously hurt the economy — to which she has responded that a changing climate is far more dangerous.
"We have to end fossil-fuel subsidies, stop new exploration and extraction, completely divest from fossil fuels and keep the carbon in the ground, now," Thunberg said on Thursday. "Especially the U.S., taking into account the fact that it is the biggest emitter in history."
As Thunberg's prominence rose in recent years, she found herself on the receiving end of mockery by former President Donald Trump, who has played down climate change.
Thunberg, for her part, responded to Trump's barbs with her own.
The teen gave Biden her endorsement last October, saying she typically avoids getting involved in politics but Trump's beliefs on climate change made "the upcoming US elections is above and beyond all that."
Since Biden was sworn in, Thunberg has amped up her pressure on the new administration.
RELATED VIDEO: Teenage Environmental Activist Alexandria Villasenor Supports Being a 'Stubborn Teenager'
After Biden issued a slate of new drilling permits a week after taking office, Thunberg tweeted "while we do appreciate beautiful speeches and promises - we prefer action."
She also warned other climate activists to not think of Biden "as a savior," in an interview with Teen Vogue on Thursday.
"We must continue to push even harder and still call out Joe Biden because, of course, he's not good for the climate either," she said. "Just because he's a bit less bad doesn't mean that he's good for the climate."
The Biden White House disagrees, noting the president has made climate change a priority — organizing this week's climate summit and creating a new "climate envoy" position in his Cabinet, to which he appointed former Secretary of State John Kerry.
Nonetheless, taking her own advice, Thunberg pressed U.S. lawmakers on Thursday to take greater action on what she views as the world's gravest issue.
"Sooner or later, people are going to realize what you have been doing all this time — that's inevitable," she said. "You still have time to do the right thing and to save your legacies, but that window of time is not going to last for long. What happens then?"
She continued: "We, the young people, are the ones who are going to write about you in the history books. We are the ones who get to decide how you will be remembered. So my advice for you is to choose wisely."