It's hard to imagine an orderly retreat to more habital climates for that number of people. I think you underestimate the synergy between war, famine, and disease.
In this case the "royal we" is hiding a lot of death. I'm sure even in a 5 deg C worst case model maybe a couple of hundred million people can survive by the poles. But that means 90-95% population die-off. That's ignoring trophic web collapses and ecological damage to the world that human beings have adapted to for hundreds of thousands of years.
I think the previous poster is being charitably vague, so that the reader can substitute in their own interpretation whether resulting pressures on people will result in orderly migration, displacement, or warfare. If history is any indication, the answer likely to be a mix of the above.
But their interpretation shows a more nuanced understanding than those who seem to suggest masses of people will die in situ, or driven to the fringes of the planet to seek relief from the heat. People and societies are quite adaptable, provided they have the means to modify their immediate environment. Billions of people live in states that will likely fare all right, because they can mitigate impacts with modest effort and resource cost, despite the presence of political movements that are fixated with collective guilt.
The other billions who are less fortunate will be subject to intense pressures for their survival. We've seen this before, and should know what to expect. It's just that we're uncomfortable talking about it.
In this case the "royal we" is hiding a lot of death. I'm sure even in a 5 deg C worst case model maybe a couple of hundred million people can survive by the poles. But that means 90-95% population die-off. That's ignoring trophic web collapses and ecological damage to the world that human beings have adapted to for hundreds of thousands of years.