Mass Migration Coming

Spin a globe and you will see that most of the Earth will be blue and that's because 71% of Earth is sea which leave approximately a total land surface area of Earth of about 57,308,738 square miles but subtract from that the 29% which is desert and the 24% which is mountainous, that leaves us with a total land area of 24,642,757 square miles which is habitable and due to Climate Change, that is shrinking.
The United Nations have said that a large swathe of the Global population, as many as three billion people, are expected to be displaced by the effects of Global Warming by the end of the century, and these people are going to have to go somewhere in a mass migration but the problem is that every inch of land is already occupied and the World is split up into nations with borders.
I have already set out my idea's for the World to come together as one nation with no borders and with as many as a third of the population being forced to migrate due to global temperatures increases, sea level rise and extreme weather in lands which will become increasingly more difficult to live in,
it may be an idea which will have to happen.  
In 2021, there were 90 million people displaced by Climate disasters such as floods, heat, drought, fires, storms and coastal erosion and in 2022 there was 100 million with more people now dying from heatwaves than wars which led the UN appeal to global leaders to ease the Climate Change migration
as: 'We cannot leave millions of displaced people to face the consequences of a changing climate'.
The problem is our political borders stopping peoples movement so we may have to reconsider them and think on a global borderless scale because it is not a problem which will go away, the issue is coming due to our carelessness towards our own environment over centuries and each year it will
grow into more of a problem as billions of people are forced out of the land they live in and it will up to us to help our fellow humans and not squabble over which nation will take them inside their borders because through no fault of their own, they literally have nowhere else to go.