The Great Exodus

The Great Exodus was what some consider a mass evacuation of Earth, yet would be more accurately described as a resettlement of human species, due to it's considerable length.

This resettlement was started in the second half of 21st century, soon after Global Climate Change was designated as the first species-wide threat. It included transporting most surviving human settlements to Mars in hibernation devices, and their survival in dormant state until the planet was terraformed, or suitable shelters were built. The Great Exodus officially ended in January of the year 2200, although the last hibernation equipment was left unused as early as the first half of the year 2193. This still considerable time it took human species to relocate, was mainly caused by fragmentation of countries, and hence resources, combined with undeveloped interplanetary travel.

Most recovered records count the survivors in millions, contrasting the 10 billion that human species counted in the beginning of the Great Exodus. This was mainly due to strict population control, meant to lessen the strain on Earth's biosphere, and prolong the time it took for climate to no longer support human life. That happened somewhere around the year of 2160, when even healthy survivors remaining on Earth began rapidly developing respiratory diseases, and temperature on the planet's surface was in most places too high for humans to survive without additional equipment in prolonged exposure. This further culled the number of survivors to near, or even below the recorded estimates.