the quote I see in a BBC interview is: “we are close to the tipping point ... could push the Earth over the brink, to become like Venus, with a temperature of 250 deg, ....”
The placement of the commas is important. Venus having a temperature of 250 degrees and Earth becoming like Venus in terms of lifelessness are different things. The surface temperature of Venus is a function of more than its atmospheric gas composition and some of those contributors can not or do not exist in the Earth and I’d bet that Hawking understood that and did not intend to infer that Earth would achieve 250 deg surface temperatures by 2600. The Earth will achieve surface temps of 250 deg but that’s about 1.5 billion years out and will be due to things other than human contributions to atm composition.
Conversely, humans may cause problems that lead to unsustainability of a large population but that will not involve such a large temperature increase.
Mixing those things up is propagandist fear mongering that makes the argument uncredible and is part of the reason that some folks auto dismiss climate change arguments.
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