The Washington PostDemocracy Dies in Darkness

Surprising study finds that solar energy can also cause climate change (a little)

In this photograph taken on August 23, 2015, a general view shows construction taking place at Roha Dyechem solar plant at Bhadla some 225 kms north of Jodhpur in the western Indian state of Rajasthan. MONEY SHARMA/AFP/Getty Images

Large solar arrays could have some surprising side effects, according to a new study, including causing changes in the local climate.

On a global scale, these changes will be minor compared to what would happen if humans continue to burn fossil fuel for energy instead, but are still worth watching, scientists say.

Figuring out how renewable energy sources will affect their local landscapes is an increasingly relevant challenge for scientists, as more and more nations are vowing to slash their carbon outputs and switch to alternatives, such as solar and wind energy. Previous studies have shown that both solar arrays and wind farms have the potential to cause regional changes in temperature and precipitation by altering the amount of solar radiation absorbed by the Earth or disrupting local airflow patterns.

With this in mind, Aixue Hu, a climate change research scientist at the National Center for Atmospheric Research, conducted a study, published Monday in Nature Climate Change, that attempted to predict the climatic effects of solar arrays. 

For their experiments, Hu and his colleagues assumed a low-carbon scenario, in which global greenhouse gas emissions would start to decline after the year 2020 as renewable energy sources are more widely used.

The researchers then carried out a series of simulations. The first simulation included solar panel installations across the world’s deserts — the parts of the world likely to receive the most sunlight — and throughout all the world’s urban areas.

The second simulation mimicked that scenario, but also assumed that the world would continue to consume a lot of energy through the use of air conditioning. 

The final simulation dropped the thermostat assumption and scaled back the number of solar panel arrays. This scenario is the “more realistic” of the bunch, according to Hu, and was meant to test whether a more modest solar panel installation would be able to address the global energy demand through the end of the century.

After running the simulations, the researchers found that the solar power generated in each of the experiments would be enough to satisfy global electricity demand by 2100. That was the good news. But the experiments also showed that the panels do have an impact on climate, at least regionally.

Solar panels change the way sunlight is reflected and absorbed by the Earth. Any radiation they take in is radiation that’s not being absorbed by the Earth. This leads to a cooling effect in the region surrounding the array. In fact, the first two simulations in this study, which assumed solar panel installations throughout the world’s desert and urban areas, produced a 2-degree Celsius regional cooling in the desert regions. This cooling was also associated with a 20 percent decrease in precipitation in the deserts. Other, slightly broader changes in precipitation and wind patterns occurred as a result in the regions surrounding the deserts.

In urban areas, the effects were a little different. In the first simulation, the model predicted a very small amount of cooling, with temperature falling approximately 0.26 degrees Celsius. In the second simulation, the one in which global thermostat regulation is significantly increased, the large amount of power consumed actually produced an urban heat island effect, in which human energy use releases heat into the environment and causes the regional temperature to warm up. In this scenario, the warming from the heat island effect essentially compensated for the cooling caused by the solar panels.

When considered on a global scale, these effects become much smaller. In the first simulation, the average change in global temperature is an average decline of about 0.34 degrees Celsius, relative to the temperature that would be expected under the same low-carbon climate scenario with no solar parks. In the second simulation, where the heat island effect is taken into account, there would be an average increase in global temperature of about 0.09 degrees Celsius. 

However, the authors acknowledge that it’s unrealistic to assume such widespread solar panel installations in the future. So they looked to the third simulation for a more realistic view of what’s to come.

In the third simulation, which included fewer solar panel arrays, the climate effects are scaled down accordingly. The average global cooling observed in this simulation is only a decline of about 0.04 degree Celsius. 

The study shows that, while large solar arrays can cause some significant regional changes in climate, “globally it will not affect the global climate much,” said Hu. “This is a big contrast with the fossil fuels.” According to most climate projections, human-caused global warming — the result of releasing greenhouse gases into the atmosphere — could lead to anywhere from 1 to nearly 3 degrees of global temperature increases under even moderate climate scenarios.

That said, the study does also provide some insight into how the local solar panel-induced climate effects might be minimized. The results suggested that local climate effects were smaller in urban areas than in the more remote desert areas and can be mitigated by the urban heat island effect. So while it’s tempting to place large solar arrays in desert areas, where they’re most likely to receive the greatest amount of interrupted sunlight, the authors note that “a more distributed solar panel installation could reduce the impact of the solar panels on regional and global climate.”

And being aware of the way certain regions could be affected by large solar deployments, could help policymakers make decisions about how to distribute panels in these places and how to prepare for the local changes that could occur as a result, Hu said.  

So future research may also examine how the distribution of solar arrays could be changed in order to maximize their positive effects on land use and minimize their negative ones.

In the meantime, this study reinforces the idea that a transition to renewable energy is imperative to protecting Earth’s climate future. While the transition won’t be without its own effects, the authors note that the alternative — a world in which fossil fuel burning is allowed to continue unabated — would be far worse.