The young Swedish activist made the comments at the Youth4Climate conference taking place in Italy ahead of pre-COP26 talks, which will start in the same venue from Thursday.
Speaking below a screen on which the UK’s COP26 president Alok Sharma appeared on a video link, Thunberg quoted statements made by the prime minister: “This is not 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.”
“This is all we hear from our so-called leaders”, she said, “words that sound great but so far have not led to action. Our hopes and ambitions drown in their empty promises.”
Thunberg also took aim at the youth conference itself, saying "so-called leaders have cherry picked young people to meetings like this to pretend they are listening to us, but they are not listening".
The activist’s latest comments follow a speech made by Johnson last week at the United National General Assembly, where he drew out a metaphor of humanity being in its adolescence, “old enough to get ourselves into serious trouble”, but about to reach a “critical turning point” at COP26.
For the adolescents and young people at this week’s Italian conference, how to secure a bigger role in decision-making is what they will be debating, as well as their role in helping to transform energy use, nature conservation and climate adaptation, and how education can create a climate-conscious society.
Thousands of activists have gone to Milan, with some 400 from about 190 countries, set to engage with policymakers to discuss proposals for possible solutions.
Thunberg told her audience that “we can still turn this around – it is entirely possible. It will take immediate, drastic annual emission reductions”.
“But not if things go on like today,” she warned. “Our leaders’ intentional lack of action is a betrayal toward all present and future generations.”
The prime minister has called for all governments to “step up” ahead of COP26 and commit to substantial reductions in carbon emissions, and said in his UNGA speech that in his view this can be done by making commitments in four areas: “coal, cars, cash and trees”.
With a recent commitment made by China to put an end to building foreign coal energy plants, analysts have expressed hope that progress will indeed be possible at COP.
However, with carbon emissions on track to rise by 16% by 2030, according to the UN, tougher pledges at COP26 are going to be required in order to keep the Paris Agreement goal of 1.5C within reach.