The teenage environmentalist seized on buzz phrase used by the UK prime minister in April, when he referred to “no Planet B” and “net zero” and used pejoratives such as “bunny hugging”. She mocked Johnson by adding “blah, blah, blah”.
Giving a speech at the Youth4Climate summit in Milan, Italy, the Swedish activist said the words of leaders had led to “no action”.
The 18-year-old prompted applause from the audience when she took aim at the PM.
During her speech on Tuesday, she said: “This is not about some expensive, politically correct, green act of bunny hugging.
“Build back better, blah blah blah. Green economy, blah blah blah. Net zero by 2050, blah blah blah. Climate neutral, blah blah blah.
“This is all we hear from our so-called leaders.
“Words that sound great, but so far have led to no action.”
Last week, Johnson used a major speech to the United Nations General Assembly to challenge the message of Muppets character Kermit the Frog, who sang: “It’s not easy being green.”
“He was wrong,” he said of Jim Henson’s creation. “It is easy to be green.”
The premier added it was “easy, lucrative and right” to be green.
Thunberg’s speech comes ahead of the Cop26 international climate conference in Glasgow which will see world leaders pursuing a target of limiting any further temperature increase to 1.5C.
The summit will involve calls to accelerate the phasing out of coal, curtail deforestation, speed up the switch to electric vehicles and encourage investment in renewables.
UK ministers are keen for the Cop26 conference to involve face-to-face meetings and speeches after the event was delayed by a year because of the coronavirus pandemic.
Speaking about the words of world leaders on climate change, Thunberg said: “Our hopes and dreams drown in their empty words and promises.
“Of course, we need constructive dialogue – but they’ve now had 30 years of blah, blah, blah, and where has that led us.
“Over 50% of all our CO2 emissions have occurred since 1990 and a third since 2005.
“All this while the media is reporting what the leaders say they are going to do, instead of what they are actually doing.
“Don’t get me wrong, we can still do this. Change is not only possible but urgently necessary.”