Yes, the biosphere of Earth changes over time. I was thinking of an immutable limit in the context of the range of changes that would still allow human life as we know it to continue uninterrupted. It’s possible the Earth’s biosphere could become too hot for human life to be supported as an integrated function of natural life outside of some extraordinary artificial support. But, I don’t believe it’s inevitable that the Earth will become that hot. There are natural feedback processes that should limit how much global temperatures will rise. Nevertheless, the complexity of food production, resource extraction, and global organization that it takes to support seven billion or more humans on Earth is fragile and susceptible to collapse in an extreme climate context. Which would likely translate into the human population radically declining in numbers as part of the feedback adjustments.