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Scientists Discover A Climate Tipping Point Could Be Far Worse Than We Thought
The Sahara's climate influence is far larger than we thought.
The great Sahara is one of planet Earth’s most prominent land features. This mega desert sprawls across almost the entire of North Africa, and we have known for years that it helps to cool and temper much of the world’s climate. Yet, we also know that climate change is slowly eroding this African giant, turning its dusty plains greener, and one day it could lead to a catastrophic climate tipping point as the Sahara ceases to cool the planet. Sadly, recent research has shown that this looming threat could be even more destructive than we thought, as they have found yet another way the Sahara has been helping to keep climate change at bay.
Okay, so that is rather a lot to unpack, so let’s start at the beginning. What is a climate tipping point? A climate tipping point is a critical threshold that, when crossed, leads to extensive and often irreversible changes in the climate system. For example, permafrost melting. The Arctic permafrost contains billions upon billions of tons of frozen carbon dioxide and methane. At a certain level of global warming, these frozen stores will thaw and suddenly release insane levels of carbon emissions, causing unimaginably destructive dramatic and sudden climate change.
The Sahara has its own tipping point. You see, it helps cool the planet (which I will get onto in a second), but as the planet warms, it could disappear. This is because a warmer climate will accelerate the water cycle around the Sahara, shifting the African monsoons northwards and transforming the desert into a verdant green wonderland. We know this because it has happened before, during the African Humid Period 11,000 to 5,000 years ago. Back then, natural oscillations in the Earth’s orbit around the Sun slightly warmed the Earth’s climate, causing the Sahara to turn into a vast grassland.
So as we heat the planet up, the Sahara should turn green again. We are already seeing this, as satellite images have shown the desert has been getting greener year-on-year for over 15 years. As the dust desert reduces, so too does its cooling effect, accelerating its demise until eventually, the Sahara is no more, and our climate is significantly warmer.
Okay, so how does the Sahara cool the planet? And at what level of global warming does this destructive feedback loop start to happen?
We previously only knew of two ways the Sahara cooled the planet: fertilisation and light blocking.
Firstly, fertilisation. The Saharan dust is rich in iron, phosphorus and other nutrients, making it an incredible fertiliser. The prevailing winds blow this dust over the Atlantic and into the Amazon. The dust that settles in the Atlantic drives plankton to bloom. These microscopic plants suck carbon dioxide out of the air to fuel themselves and build their bodies. Some of this absorbed carbon is released back into the atmosphere, but some sinks to the ocean floor, where it remains for millions of years, creating a natural carbon sink. Studies have estimated that the Saharan dust increases the carbon sequestration rate (the rate the carbon sink stores away carbon) by 4.5% on average, while in some locations, it is boosted by 20%!
What’s more, the nutrients flowing to the Amazon from the Sahara match the amount of nutrients flowing out of the Amazon into the ocean. In other words, the Saharan dust is keeping a nutrient equilibrium in the Amazon, allowing the Amazon rainforest’s massive, complex, carbon-rich ecosystem to thrive. The Amazon contains around 123 billion tonnes of carbon, and if the Saharan dust were to stop flowing to it, the ecosystem would slowly starve of nutrients, wither away and release this back into the atmosphere, causing a significant level of climate change.
The second way was light reflection. Saharan dust is very reflective, so as it travels through the wind, it bounces solar energy back into space, reducing the amount of solar energy being trapped in our atmosphere by greenhouse gases. A previous study found that the sunlight-blocking effect of Saharan dust caused a cooling of the North Atlantic of 0.32 to 0.4 degrees Celsius between June 2005 and 2006 and accounted for approximately one-third of the total sea surface cooling effect in the North Atlantic.
This is where this new study comes in. You see, it turns out that the Sahara has a third cooling effect. Its dust actively destroys one of the worst greenhouse gasses and is literally holding back man-made climate change.
This started when scientists found that methane was disappearing over the Caribbean far faster than it should be. They quickly discovered that it strongly correlated with the amount of Saharan dust in the air over the Caribbean. It turns out that Saharan dust is combining with salty sea spray to make Mineral Dust-Sea Spray Aerosol (MDSA). The chemistry of the dust reacting with the sea salt creates an abundance of chlorine radicals. This chlorine then reacts with the methane in the air, binding to it and removing it from the atmosphere.
Now, we humans and our livestock pump out a massive 73 tons of methane every day. Annoyingly, this gas is about 100 times more potent a greenhouse gas than carbon dioxide. It does naturally remove itself from the atmosphere, but it takes about a century. This means our methane emissions are a serious driving force of climate change. So the fact that the Sahara is actively reducing the amount of methane in the air means it has been holding back man-made climate change.
As this discovery is so new, we don’t yet know how powerful this effect is and where else in the world it is taking place. But it means that if the Sahara turns green and disappears, the fallout could be far worse than we thought.
Now, ready for the kicker?
The level of global warming that the Sahara turns green, and this climate tipping point is reached, has been calculated at between 2 and 3 degrees Celsius. We have already experienced just over a degree of climate change, and current studies suggest we will see 3 degrees of climate change by the end of the century.
We still don’t know how much Saharan greening will increase global temperatures. I mean, there may have been even more ways the Sahara influences our climate that we are still ignorant of. This is why, despite our super-computer-driven climate models, scientists say we are now entering uncharted climate territory. We only have a vague idea of what impacts await us as the globe warms, so we could very easily stumble into a climate tipping point we had no idea of and spark Armageddon. All the more reason for us to reach net-zero as soon as possible.
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