Turning the Sahara Green: Some Unintended Consequences of Wind and Solar Farms

Reference:
Li, Yan, E. Kalnay, S. Motesharrei, J. Rivas, F. Kucharski, D. Kirk-Davidoff, E. Bach, and N. Zeng. “Climate model shows large-scale wind and solar farms in the Sahara increase rain and vegetation.” Science, vol. 361, issue 6406, 1019-1027.  DOI: 10.1126/science.aar5629.

 

A few days ago, the IPCC released a special report announcing that we only have about twelve years to act in order to avoid crossing the 1.5-degree warming threshold that many countries are trying to avoid.  We need to reduce our carbon emissions more urgently than ever, and some scientists have risen to this challenge with proposals so ambitious that they almost sound like science fiction.  One proposal is to cover much of the Sahara Desert with wind turbines and solar panels. A move this big could have many unintended consequences for the climate, but fortunately, a new study by Li Yan et al. suggests that enormous wind and solar farms could actually have positive impacts for those living around the Sahara.

Why build wind and solar farms in the Sahara?

According to the researchers of this study, the Sahara is the ideal setting for this kind of experiment.  It’s an enormous, mostly uninhabited expanse where both high winds and high insolation (i.e., exposure to sunlight) allow for wind turbines and solar panels to be very efficient without interfering with human development or agriculture.  Furthermore, the Sahara lies in close proximity to Europe and the Middle East, where many people live and demands for electricity are quite high.

In order to assess the impacts of building large wind and solar farms in the Sahara, Yan et al. simulated the evolution of air currents and temperatures by using a climate model.  They used a special kind of climate model that also simulates how plants respond to changes in climate. Plant life can be a very important component of climate models, especially near the edge of a desert like the Sahara.  For instance, plants can make a regional climate more humid and rainy simply because they are darker and wetter than desert sand, in a process known as albedo-vegetation-precipitation feedback.  The inverse of this process also helps us understand how a desert can grow, as sand particles can encourage a desert to expand simply because they are dryer and more reflective than plants.  This is particularly relevant to the Sahara, which has been expanding in recent years.

How can wind turbines and solar panels affect the climate?

Most of us are used to thinking about wind turbines and solar panels as remedies for climate change: rather than burning fossil fuels to produce energy, we convert energy either from the wind or the sun’s rays.  However, it turns out that both wind turbines and solar panels can actually affect our climate, and not always in the way we’d want.

Wind turbines.  Image credit: Wikimedia Commons.

Let’s start with wind turbines.  You might’ve heard some buzz last week about how wind turbines can actually result in warmer temperatures!  This effect is especially pronounced at night, when the surface tends to cool more rapidly than the air at higher elevations.  Wind turbines can make conditions more windy and mix the warmer air from above so that it comes closer to the ground, thereby warming us up.  Fortunately, Yan et al. found that this warming effect is very localized and much smaller than the warming from enhanced carbon dioxide. This means that, even in spite of their potential warming effects, wind turbines are still a plausible alternative to fossil fuels.  When they studied the possible effects of wind turbines in a climate model, Yan et al. found that increasing windiness in the Sahara has another side effect – more rain!

Solar panels.  Image credit: Wikimedia Commons.

While wind turbines might affect our climate by increasing the windiness of the lower atmosphere, solar panels might affect our climate by having such a dark color.  The very pale color of the Sahara’s sand makes it perfect for reflecting sunlight back to space, whereas the dark solar panels absorb more sunlight and more of the Sun’s energy.  As a result, Yan et al. expect that solar panels will also cause the Earth’s surface to warm. When air is warm, it rises, and any water vapor that’s contained in the rising air can eventually condense into water droplets and fall back to the earth as rain.

Yan et al. found that both of these geoengineering projects – large wind farms and large solar farms – placed strategically around the Sahara can have some unexpected effects on the local climate.  Firstly, wind and solar energy can actually warm the climate, and secondly – just for the Sahara – they might induce more rain, trigger the albedo-vegetation-precipitation feedback, and slow the expansion of the Sahara Desert.

Why is it so important that there might be rain in the Sahara?

During the last century, the Sahara has been expanding.  This has serious consequences for those who’ve made their livelihoods in the areas nearby, particularly in the Sahel, or the transition region between the Sahara Desert and the savannas further south.  Desertification, the conversion of previously arable land to desert, can result in food shortages, mass migrations, and increased vulnerability to armed conflict.

Lake Chad.  Image credit: Wikipedia.

The drying of Lake Chad is a particularly tragic example of the seriousness of this situation.  Over 21 million people rely on this lake as a water source, but in conjunction with the Sahara’s expansion, the lake has shrunk by 90% in the last 50 years.  In addition to facing food shortages, those living in this region have also suffered from armed conflict, including attacks by Boko Haram. According to the UN, over seven million people are now in dire need of food in that area.

Many inventive scientists and engineers have suggested feats of geoengineering as possible strategies for reducing our carbon emissions, but these proposals often come with unintended (and unwanted) consequences.  At least according to Yan et al., the construction of wind and solar farms in the Sahara is a rare example of a big dream that could have really positive side effects.

Featured image credit: Sahara Desert. Wikimedia Commons.

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Rohini Shivamoggi

I'm a PhD student studying atmospheric sciences at MIT. I study the formation of secondary eyewalls in hurricanes, which hopefully will help us improve our forecasts of hurricane intensity! Before I got to MIT, I grew up in Florida and studied Chemistry and Physics at Harvard University. My other interests include weather forecasting, photography, and encouraging diversity in STEM! You can find me on Twitter @RShivamoggi.

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