Source, in full
Samira Ahmed may have been thinking of a Thunberg quote from section 4.1 which did indict "capitalist consumerism", though it also criticized other "current political ideologies": "Leaving capitalist consumerism and market economics as the dominant stewards of the only known civilization in the universe will most likely seem, in retrospect, to have been a terrible idea. But let us keep in mind that when it comes to sustainability, all previous systems have failed too. Just like all current political ideologies – socialism, liberalism, communism, conservatism, centrism, you name it. They have all failed. But, in fairness, some have certainly failed more than others." On 2 Nov 2022 Thunberg referenced this section of the book in a tweet which criticized "climate deniers and delayers" for making up false quotes and attributing them to her.
Variants
suggesting Thunberg had said we needed to overthrow the “whole capitalist system” have been attributed to her, as in this Unherd article which includes the comment 'Only overthrow of "the whole capitalist system" will suffice', and this Telegraph article which comments on 'the “whole capitalist system” Ms Thunberg referred to', and this Washington Examiner article which says Thunberg was 'calling for a total upheaval of the "the whole capitalist system."'. These articles are discussing her speech and talk at the launch of her book The Climate Book which can be seen in this youtube video. In fact the quote came from Samira Ahmed who was interviewing her, who was discussing a section of the book and said at 59:20 "You say, 'humankind has not created this crisis, it was created by those in power to create unimaginable amounts of monies and to maintain a system that benefited them', you say we need to change the whole capitalist system." The last part of the sentence seems to be Ahmed's own summary of her reading of Thunberg's message rather than a direct quote, since Thunberg's comment in section 3.1 of The Climate Book did not refer to "the capitalist system": "Humankind has not created this crisis – it was created by those in power, and they knew exactly what priceless values they were sacrificing in order to make unimaginable amounts of money and to maintain a system that benefitted them. It is – among other things – the social and economic structures which generate such perverse inequalities that are driving us towards the ecological precipice. It is the idea of infinite growth on a finite planet."