Of the young people invited to speak before the congress, Greta Thunberg was first out. But she immediately explained that she had not made a speech.

Instead, she wanted to pay attention to leadership meetings on the UN Climate Panel's report on what happens at 1.5 degree warming, from October 2018.

"This report is my testimony," said Thunberg.

"Take real action"

Thunberg also said she wants congressional leadership meetings to unite behind the research in the report.

"Then I want you to take real action," she said.

Thunberg was later asked by one of the congressional leaders about why they should listen to the research, to which she replied that she "did not see a reason not to listen."

- These are not political opinions. It's not my opinions, it's science, Thunberg said.