Could Earth become the next Sahara? Clues from vanishing grasslands

The recent discovery that the Sahara Desert was once home to lush grasslands and verdant pastures around 4,000 years ago has prompted scientists to delve deeper into whether Earth might experience a similar dramatic environmental shift as seen in northern Africa.

A new study has shed light on how the transformation from what was known as the “African humid period,” spanning from 15,000 to 5,500 years ago, led to the modern-day arid conditions in northern Africa. This change, which forced humans to migrate towards mountains, the Nile valley, oases, and deltas, is now viewed by scientists as a prime example of a climate tipping point in recent geological history.

Climate tipping points are critical thresholds that, once crossed, can lead to significant and often irreversible changes in the climate, establishing a new stable state.

The study, published in Nature Communications, found that prior to northern Africa becoming arid, its climate oscillated between two stable states before it permanently shifted to drier conditions. This phenomenon, known as climate “flickering,” was observed for the first time through this research, raising concerns among scientists about whether there will be advance warnings for future climate tipping points.

Key concerns include whether the crossing of the global warming threshold of 1.5˚C might lead to major tipping points such as collapsing ice sheets in Antarctica or Greenland, the sudden thawing of Arctic permafrost, or the widespread die-off of tropical coral reefs.

There’s debate among experts about whether Earth will provide clear warning signs before these significant climatic shifts occur. The ability to recognize such signs may vary depending on the nature of the tipping point, making interpretation challenging.

One crucial question is whether tipping points will be preceded by a period of flickering, indicating instability, or if the climate will seem stable right up until it tips.

To further explore these climatic shifts, an international team of scientists conducted fieldwork in the Chew Bahir basin in southern Ethiopia. They discovered evidence of a large lake that existed in the region during the last African humid period. The presence of this lake is recorded in the sediment deposits found beneath the current lake bed.

Today, the lake has largely dried up, but the sediment deposits remain accessible and can be economically drilled for study by locals.