The Sahara’s Green Transformation Could Shift the Climate Worldwide

How the Sahara’s Green Past Shaped Climates Across Continents

I was speaking with a friend in Valencia. Yes, the flooded Valencia.

She was telling her all about people who had been trapped in their houses without food, water, or electricity for days. About 96-year-old grandmothers are being rescued and spending days in a shed house in the attic of a building.

About those who, without knowing any better, resourced to get in their cars to escape the situation just to find themselves trapped in a river of mud. The last rides of their lives. About people who draw in subterranean parking lots still filled with water and mud. Their bodies are trapped for days.

And the worst, about even infant lives being lost.

Growing up not that far from the catastrophe, it hit home for me. She could recognize herself in these people’s faces.

The good news is that people are mobilizing across the country, and her family is participating in all the fundraising initiatives, but she wished she could do more.

My friend told me that the biggest issue was that people were unprepared. The region, usually semi desertic, saw a year’s worth of rain in a few hours, something never seen before. Without knowing any better, they resourced to get in their cars and leave when the winning move would have been to get as high up in buildings as possible. Spanish buildings have strong foundations.

But among everything, these taught us, as scientists, that climate change can have unpredictable consequences and that even the most unexpected areas can be affected by changes happening everywhere else in the world. Today’s story highlights it very well.

Imagine the Sahara Desert — vast, arid, and mostly lifeless. Now, picture it covered in green shrubs, stretching for miles. It may sound surprising, but the Sahara wasn’t always the dusty expanse we know today. Not by far.

In fact, between 5,000 and 11,000 years ago, during the mid-Holocene, the Sahara saw a period of intense greening, largely driven by a natural uptick in solar energy that boosted monsoon rains across northern Africa. Scientists have discovered that his unique transformation, known as the African Humid Period, led to a fascinating climate impact on regions far beyond Africa’s borders.

When The Sahara Wasn’t a Desert

A series of scientific discoveries tell us a story that not everybody knows about the Sahara Desert

Recent research published in Climate of the Past used climate models to look at how this “greener Sahara” affected the Northern Hemisphere, especially in summer.

Dr. Marco Gaetani and colleagues ran simulations that revealed something unexpected: the expansion of vegetation in the Sahara wasn’t just a local change. In fact, the team found that Saharan greening had a lasting effect on atmospheric circulation and climate patterns across much of the hemisphere.

“African Sahara ‘greening’ can alter Northern Hemisphere climate,” noted the authors, highlighting the wide-reaching implications of this ancient shift.

To investigate these impacts, researchers relied on advanced climate models that mimicked two scenarios from the mid-Holocene: one without any green in the Sahara and one with prescribed vegetation and reduced dust emissions.

By comparing these models, they aimed to understand the role that a lush Sahara might have played in altering temperature, precipitation, and wind patterns thousands of miles away. This approach allowed them to observe how a change in one part of the world could ripple across continents, affecting the climate in areas like North America, Europe, and Asia. Quite a well-structure study design, if you ask.

And what did they find?

The models showed that a green Sahara had a significant impact on the Walker Circulation, an atmospheric loop that transports warm air and moisture from the west to the east.

This circulation shifted westward During the event, creating new patterns in the Northern Hemisphere jet streams. In summer, the North Atlantic jet stream shifted and strengthened, while in winter, the North Pacific jet stream took center stage. These changes in atmospheric flow had visible effects on climate across the hemisphere, altering temperature and rainfall patterns from season to season. A series of ripple effects.

But what types of changes are we talking about? I know you’re wondering!

Specifically, summers in regions like Scandinavia and parts of North America became warmer and drier, while winters in Western Europe got colder. The Mediterranean turned chillier and wetter than usual, while Asia saw warmer winters and cooler, wetter summers.

By shifting the North Atlantic Oscillation, a key pressure system, the Saharan greenery caused a flip from a positive to a negative phase in the NAO. This shift led to colder winters and drier conditions in Scandinavia, but warmer and wetter seasons in places like northern Europe and parts of North America.

The diversity of effects shows how interconnected our climate systems truly are. We must remember that what happens in one part of the world, especially if it’s a vast area, has consequences everywhere else.

This “green Sahara” had another side effect: reduced dust levels. Vegetation naturally keeps dust down, which lead to an 80% reduction in dust emissions from the Sahara. This change, paired with a drop in surface reflectivity (albedo) from the plants, amplified the warming across the tropics.

With less dust to block sunlight and more greenery to absorb solar energy, temperatures increased and water recycling improved. In short, Saharan vegetation kept drought conditions at bay across the region, creating a cycle that supported further greening, just like we see in the Amazon today.

You may be asking, what’s the takeaway from all this?

The findings highlight the incredible interconnectedness of Earth’s systems. A greening Sahara didn’t just impact Africa; it triggered climate changes across continents, affecting everything from the jet streams to seasonal rainfall patterns.

This study offers a glimpse into how changes in one part of the world — especially in tropical and subtropical regions — can send waves across the planet. In today’s context, this research suggests that shifts in vegetation and atmospheric circulation in response to climate change could have far-reaching consequences, some of which might be challenging to predict without advanced models.

As Dr. Gaetani’s team pointed out, the interconnected nature of the atmosphere and oceans suggests that the impact of Saharan greening is just one piece of a larger climate puzzle. Changes like this one remind us that even transformations in desert landscapes can shape the global climate in unexpected ways.

In our current era of climate change, understanding the effects of the green Sahara showcases how Earth’s systems have long worked together to create the climates we know — and how they might continue to surprise us in the future, for better or for worse.