The transformation of the Sahara Desert occurred between the end of the last ice age, approximately 11,000 to 5,000 years ago.

Bright green vegetation grew on top of the dunes, and increased rainfall transformed the arid depressions into lakes.

Approximately 9 million square kilometers of northern Africa transformed into an oasis during the Green Sahara period, attracting herds of animals like hippos, antelopes, and elephants to thrive on abundant grasses and shrubs.

Although this lush paradise has vanished, there is a possibility of its return. Kathleen Johnson, a professor at the University of California, suggests that the Green Sahara phenomenon is linked to the Earth's oblique axis, which constantly changes its rotational orbit in a pattern repeating every 23,000 years.

However, the timing of the Sahara turning into a new oasis remains uncertain due to a crucial factor—human-induced greenhouse gas emissions causing unpredictable and uncontrollable climate change.

The Sahara desert became an oasis because of a change in the angle of tilt of the earth's axis.

About 8,000 years ago, the tilt of the earth's axis went from about 24.1 degrees to 23.5 degrees today, a small change in angle that has a big impact.

Today, the northern hemisphere is closest to the sun during the winter months. But during the Green Sahara, the Northern Hemisphere was closest to the Sun during the summer months.

This resulted in an increase in solar radiation to the Earth's northern hemisphere during the summer months. This increase in solar radiation also enhances the African monsoon.

The increased heat above the Sahara creates a low-pressure system that draws moist air from the Atlantic Ocean into the desert.

The transformation of the previously arid Sahara into a grassy, shrub-covered savannah resulted from increased moisture. This environmental shift attracted a variety of beasts, and as their numbers grew, humans followed suit, eventually domesticating sheep.

The change in the Earth's oblique axis, according to Peter de Menocal from Columbia University's Lamont-Doherty Earth Observatory, is influenced by gravitational interactions with the moon and other massive planets. These interactions lead to periodic changes in the Earth's orbit, including the "wobble" of the Earth's oblique axis.

This wobble causes the northern hemisphere to move closer to the sun in the summer every 23,000 years. Scholars speculate that during the Green Sahara period, solar radiation in the Northern Hemisphere was 7 percent higher than it is today.

This increase in thermal energy could have increased monsoon precipitation in Africa by 17 to 50 percent, according to a 1997 study in the journal Science.

The green Sahara lasted only 200 years, Johnson said. The change in solar radiation was gradual, but the change in the landscape was sudden. The next time the green Sahara reappears is expected to be in 12,000 or 13,000 years in the park, 10,000 years later.

But what scientists can't predict is how much greenhouse gases will affect this natural climate cycle.