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Africa’s Sahara desert is a prime location, some say, to build arrays of solar panels and wind turbines. But scientists are aware that building these structures can potentially have large-scale effects on the surrounding environment that are worth studying first.

Hosted by: Hank Green

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Sources:
https://science.sciencemag.org/content/361/6406/1019
https://science.sciencemag.org/content/sci/suppl/2018/09/05/361.6406.1019.DC1/aar5629_Li_SM.pdf
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Africa’s Sahara desert is wide open and sparsely populated, a great source of sun and wind, and a prime location, some say, to build arrays of solar panels and wind turbines. And while replacing fossil fuels is great for fighting climate change, these power plants could bring more to the region than just tons of green energy.

According to computer modeling, they could indirectly alter the region’s climate for the better. Researchers say the Sahara is a great choice for energy production because not many people or animals live there, and it’s adjacent to lots of much more populated areas that need energy, and will need more as time goes by. But building renewable energy extraction methods isn’t as simple as plopping them down wherever it’s super sunny or windy.

Scientists are aware that building these structures can potentially have large-scale effects on the surrounding environment. So they run climate models using supercomputers to see what those effects might be. In a 2018 study, one team of researchers used such computer models to determine what could happen if humans scattered the Sahara with wind turbines, solar panels, or both.

One thing was certain:if they were real, those solar panels and wind turbines would produce tons of power. Like, over four times what the entire human race uses in an average year. And that’s a conservative estimate, using stats for mid-range commercial solar panels that only convert 15% of the Sun’s energy they absorb into electricity.

But that wasn’t all these power plants would do. The team used climate data from the entire twentieth century to make sure the model had a good grasp of the real world, and then let it simulate the next one hundred years. And they found some surprising changes to the Sahara’s climate.

For one, it got hotter. That’s largely because solar panels can decrease the albedo, or reflectivity, of the surface, because they absorb more sunlight. And tall structures like wind turbines affect the overall air flow over the land, which can indirectly raise temperatures, too.

So installing either type of power plant can actually make the region around them hotter. When the team modeled installing either solar or wind farms, or both types together, the local average temperatures increased by roughly one to three degrees Celsius. But the simulations had a different fate for the region to the Sahara’s south.

It’s known as the Sahel, and serves as a semi-arid transition between desert and savanna. Down there, temperatures slightly decreased. The culprit?

An increase in plant coverage. But where did the plants come from? An increase in rain.

Rainfall actually increased in both the Sahara and the Sahel, compared to a control simulation with no power plants. But the Sahel saw more. The power plants caused an initial increase in surface friction and decrease in albedo.

That allowed more water to collect in the air above the region, and that means more precipitation. With more rain comes more plants. But the plants themselves reduce the areas’s albedo and increase surface friction, so they cause even more precipitation.

It’s a positive feedback loop. In fact, these models showed that 80% of the increase in rainfall was driven by the new plant life. That shows how shiny new tech can have ripple effects we don’t always expect, and sometimes those things can be positive, sometimes they can be negative, but they need to be explored!

It is important to note that there were a lot of variables for the researchers to account for in their simulation. Like how they physically spaced out their wind farms and what percent of land was covered by solar panels. Or how efficient the panels are at converting sunlight into electricity instead of heat, and how reflective they are.

Tinker with any of that and the results could change. But altogether, the solar and wind farms could increase rainfall in the Sahel region by twenty to fifty centimeters per year. Talk about blessing the rains down in Africa...

That much rainfall would drastically affect the ecology of the region and the lives of people living there. Like changes in agricultural yields and access to fresh water. We’re not qualified to say whether such deliberate climate manipulation is a good idea, since the effects are so complicated.

And it’s not clear who’d actually get to use the energy produced. Those calls are best left to the people actually living there. But computer simulations like these can show us just how much our tech can affect the planet -- and at a potentially remarkable scale.

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