KAROLY, David. "There’s at least one – probably more – climate scientists in Europe that have said that the long-term sustainable population of people on the Earth is about 1 billion people in 2100 "

Professor David Karoly (climate scientist, honorary professor at the University of Melbourne and CSIRO's climate change hub leader) on the sustainable population of people on the Earth and in response to the question “Could the [present] mass extinction include humans?” : “So, we’re talking about break-up of the landscape corridors that would allow movement of animals, movement of plants, that would allow the connectivity to move southward [in the Southern Hemisphere] into cooler environments. That’s a critical factor. For people, we can move. But, certainly, there’s at least one – probably more – climate scientists in Europe that have said that the long-term sustainable population of people on the Earth is about 1 billion people in 2100 – not the foreshadowed United Nations population estimates of about 10 to 12 billion people. That’s not good news” (David Karoly in Q&A Science Special, Transcript, 17 June 2019: https://www.abc.net.au/qanda/2019-17-06/11191192 ).