The Earth and the Roman Empire

I suppose that one might predict that the UK's PM, with his Classics degree, would try to produce a glib analogy between the collapse of the Roman Empire and the potentially devastating effects of climate change (https://www.theguardian.com/environment/2021/oct/29/boris-johnson-cop26-climate-warning-rome-g20-dont-act-now-too-late). The consequences of failure of Cop26 would, however, be on an entirely different scale. Romans were simply replaced by other groups of dominant humans and cultures/civilisations reasserted themselves. Climate change, however, offers no such guarantee of a potential transition. Humans might well find survival difficult enough (if not impossible). The UK PM's claim that Cop26 "must mark the beginning of the end of climate change" is true but overly simplistic. 'Greenhouse gases' remain in the atmosphere for extended periods. Even if their release stopped tomorrow, climate change would carry on. The PM's boosterism and his suggestion, to children, that we should feed humans to plants are distinctly unhelpful. Johan Rockstrom of the Potsdam Institute For Climate Impact Research also states that "The rise of 1.5C is not an arbitrary number. It is not a political number. It is a planetary boundary"(https://www.theguardian.com/environment/2021/oct/30/climate-experts-warn-world-leaders-15c-is-real-science-not-just-talking-point). Rockstrom then somewhat demolishes his own argument, by saying that "Every fraction of a degree more is dangerous". 1.5C was originally a tacked-on aspiration, over and above a mandate to keep global heating to less than 2C above pre-Industrial levels. It has become increasingly apparent since the Paris Accord, however, that a 2C rise would be catastrophic. So, 1.5C (the new but unlikely target) clearly was a somewhat arbitrary number.