Proposed plan to dim the sun: is it sci-fi or solar geoengineering?

It’s time for some sun science, and it’s easiest to just dive right in. Solar irradiance is a bit confusing, but it is an essential term for understanding solar energy. Basically, it is the measure of light (sun) energy within a certain amount of space. The amount of solar irradiance is important; the more there is, the more energy solar panels can produce. 

Solar radiation, on the other hand, is a more technical term for the sun’s rays, and it differs from solar irradiance because it refers to the sun’s energy in general. Solar irradiance is a measure of solar radiation technically measured by a wavelength of light. For our purposes, we just need to know that it is the amount of sunlight that falls onto your solar array at any given time. 

According to a new study, solar irradiance has been on the decline in many locations, with pollution stemming from forest fires and car exhaust fumes as the main drivers. We will talk about why that is, what it means, and what a proposed plan for deliberately dimming the earth’s sunlight might mean for the future of solar power. 

What affects solar irradiance? 

Solar irradiance can be altered by aerosols, a catch-all term that describes particles within the atmosphere. These particles are things like salt from the ocean floating in the atmosphere, water droplets that make up clouds, and even black carbon emitted from fossil fuel plants. 

Climate science is convoluted, and studying how aerosols interact with the atmosphere is no different. Another layer to understanding aerosols is to understand albedo. Albedo refers to certain surfaces on the earth’s ability to reflect sunlight back into space. 

Aerosols can alter the albedo effect in different ways. Generally, lighter surfaces like ice caps reflect sunlight back into space, cooling the planet. But dark surfaces, like a deep dark ocean, actually absorb more heat. 

Believe it or not, black carbon and pollution from things like coal mine exhaust and sulfur dioxide following a volcano erruption, have a slight cooling effect. The dark aerosols block the sunlight from reaching the earth, as seen with the eruption of Mt. Pinatubo - the sulfur dioxide that was emitted cooled the entire earth due to the sheer amount of aerosols. 

So, can black carbon actually cool the planet? 

Now here’s where it gets even more confusing. One of the issues with pollution, like coal exhaust, is that it absorbs heat. So while pollution aerosols reflect sunlight back into the atmosphere, the sunlight that is reaching the earth is absorbed by the particles - similar to how CO2 absorbs heat - and contributes to global warming.

Overall, however, aerosols are believed to have a stronger cooling effect on the planet that outweighs their warming effect. For example, the pollution from forest fires in California in 2020 actually cooled the entire United States for a few days. 

But that pollution from the burned trees (and the carbon that was emitted from the burning) stays within the atmosphere. On top of that, the trees no longer exist, so they can’t absorb the excess CO2. 

So yes, aerosols can cool the planet, and there are proposed ideas to use this concept as a way to mitigate certain effects of climate change - more on that later.

What does this mean for solar? 

Compared to long-term averages, over the last 10 years, solar irradiance was down about 7-10% in the United States’ western states, Australia, and India. In India, pollution was the main cause of this, while smoke from forest fires dimmed the sun in the United States and Australia. 

There aren’t many studies showing whether or not pollution has affected solar panel output, but one can assume that with less sunlight reaching the earth's surface, solar panels will perform at less than their peak. 

With that said, there are studies that show the potential effect of solar geoengineering on solar performance. 

What is solar geoengineering? 

Solar geoengineering, on a broad scale, refers to a method that intentionally alters the earth’s climate to attempt to reduce the harms of climate change. 

There are a few proposed methods of geoengineering, but the one that is particularly concerning is the idea of spraying aerosols - specifically sulfur dioxide - into the atmosphere in a deliberate attempt to block the sun’s rays. So, solar geoengineering would deliberately add aerosols (similar to pollution aerosols) to the atmosphere. 

As we said earlier, this would have a cooling effect on the planet as a whole, but it would dim the sun and reduce solar irradiance at the same time. This would hinder solar panels from generating electricity by as much as 10%, according to one study.

This does not necessarily mean that if there is pollution, solar should not be used. It just adds another layer to the mix in determining how well solar arrays will work across their lifetime. The more solar panels, the less pollution from power plants, so hopefully the problem can work itself out. 

Other issues with solar geoengineering

First, this is a completely new technology, which typically comes with a slew of issues to work out. It’s currently in the testing phase and is not yet a viable option that can be deployed right now.

Second, because aerosols generally reduce temperatures in localized areas, the sheer amount of aerosols needed to block the sun globally would need to be emitted to the tune of 50 million metric tons a year. Technology to do this does not yet exist. 

Also, studies researching impacts of this show that there is potential for a reduction in the ozone layer, and that it could cause a change in rainfall patterns globally, making some places more arid and some more wet. 

What’s next for solar? 

There is no neat tie-up to end this, just to say that pollution and geoengineering could reduce solar panel output. But, one can argue that pollution will continue to decline if we shift towards renewable energy through solar power, wind power, and the use of EVs. 

What’s tough is climate change has been shown to cause more frequent and intense wildfires, which clog up the sky with smoke and reduce the ability for solar panels to absorb energy. 

The true irony would be if the world does not act on climate change quickly enough by reducing fossil fuel use, and solar geoengineering winds up being a last-ditch effort to stop the planet from heating up more. On a large scale, geoengineering would reduce the ability of one of our main fighting agents against fossil fuel emissions; solar. 

It would also likely give governments and businesses an excuse to drag their feet even longer, continuing to push away climate action because, “The sun is being dimmed, so why stop burning fossil fuels?” All in all, there are plenty of “what if’s” and none of them seem ideal - except for reducing fossil fuel use globally.