The two young activists had a chance to meet in person while Thunberg was visiting the United Kingdom for a protest.
Thunberg had previously said Trudeau was "obviously not doing enough" about climate change.
The teenage climate activist has been immortalized at the Panoptikum wax museum in Hamburg, Germany.
Twitter critics suggested the US treasury secretary should get a science degree so he can finally understand climate change.
"Our house is still on fire": 5 key moments from climate activist's appearance as teenager scolds world leaders.
"It’s not about Meatloaf," the young climate activist tweeted. "It's not about me. ... It's all about scientific facts."
Greta Thunberg spoke to David Attenborough for the first time over Skype to talk about the climate change crisis and how they are each other's inspiration.
The Swedish climate activist has responded to two controversies as she travels home to Sweden for the holidays.
The 16-year-old environmental activist had a sassy response to Trump's "Chill Greta" attack.
The president's eldest son called the honour a "marketing gimmick" and said it should have gone to Hong Kong protesters.