That will be no problem, since we will have figured out how to use the oceans to create rain clouds way before 2100. The 350 M sq miles of the Sahara alone is enough to house the entire 7B population, every man, woman, and child, with a population density that is less than Ada County, Idaho. Just do the math. Zimbabwe used to be the bread basket of Africa before that troll Mugabe took over and spoiled it with his corruption.
Even better, you could house the world’s entire population in the state of Texas.
Texas has 261,797 square miles of land area
1 square mile = 27,878,400 square feet
So Texas has 7,298,481,484,800 square feet of land area
The world population is 6,706,993,152 / 4 = 1,676,748,288 households of 4 people each
Dividing the 7,298,481,484,800 square feet of land area in Texas by 3000 (3000 sqft. lots)
Giving us 2,432,827,161 1500 sqft homes on 3000 sqft lots,
Subtracting the 1,676,748,288 households from the 2,432,827,161 1500 sqft homes leaves us with
756,078,873 houses still empty.
Even better, you could stand the entire world’s population in Jacksonville, FL. (Jacksonville is the largest city by area in the continental US. It now has 840 square miles.)
840 square miles
23,417,856,000 square feet
3.5 square feet for each of 6,706,993,152 people