A simple laboratory experiment has sparked new insight into the potential impact of climate change on the intensity of ocean lightning. A team of researchers in Israel gradually changed the acidity of a beaker of water while shooting it with an electrical spark. As the water became more acidic, the flash become brighter. If what they observed in the lab is indicative of how lightning acts in nature, ocean lightning could become around 30% more intense by century’s end under a worst-case climate scenario, according to the scientists.
Such a rise in intensity could threaten the safety of marine life and oceangoing vessels alike, the authors of a new paper in Scientific Reports argue. But other experts in the field caution that this makeshift lightning in a beaker could behave very differently than real-world lightning in the atmosphere.
An Illuminating Line of Inquiry
The idea for the experiment started with a conversation over lunch between lead author Mustafa Asfur, a lecturer at Israel’s Ruppin Academic Center, and Jacob Silverman, an ocean biogeochemist with the National Institute of Oceanography in Haifa. “I started to ask innocent questions about what happens to seawater when lightning strikes it,” Silverman said.
When Asfur and Silverman began digging into the scientific literature, they were met with a surprising answer: Nobody knows. The prevailing assumption in the field was that any surface on Earth—rock, soil, ocean, or lake—could be considered a perfect conductor. But data show lightning behaves differently over land and sea—it is far more frequent over continents, and evidence suggests it is often more intense over the ocean.
A 2019 paper in the Journal of Geophysical Research: Atmospheres mapped the global distribution of a kind of lightning known as a superbolt, which is 100 to 1,000 times brighter than an ordinary lightning bolt. Researchers found that almost all superbolt hot spots were over oceans and seas, but they had no ready explanation for why that might be the case.
Silverman and Asfur wondered whether the ocean itself could have something to do with the pattern. “I have a feeling that maybe we’re missing something,” Silverman said. “Maybe the conductivity of the ground does matter.”
A Strikingly Simple Setup
To test the idea, Asfur and his team came up with a simple laboratory setup that replicated lightning striking the ocean. They filled a beaker with water and suspended one electrode about a centimeter above the water and another about 3 centimeters below, in a setup that produced a 1-million-volt spark with a current of about 20 amperes. They measured the sparks’ intensity using an optical fiber spectrometer that measured relative irradiance units.
The team first measured how salinity affected the brightness of the spark, zapping water ranging from normal tap water to a salty sample from the Dead Sea. Sure enough, the sparks in the saltier beakers produced brighter flashes, the team reported in a study published last year.
Next, researchers turned their attention to another property of water that can change its conductivity: acidification. They used two methods of changing the pH of the water in the experiment by adding a strong acid and by bubbling carbon dioxide. Like salinity, acidification had a measurable impact on the brightness of the sparks. Surprisingly to the researchers, the spark intensity increased more than 2 times faster using the carbon dioxide bubbling method to lower the pH.
These results “caught me off guard at first,” said Earle Williams, a physical meteorologist with the Massachusetts Institute of Technology who was not involved in the study. “My expectation was that it wouldn’t matter much what the material was.”
More Than Just a Flash in the Beaker?
If lightning is, indeed, growing more intense over the oceans as climate change makes oceans more acidic, shipping vessels, oil rigs, and other ocean infrastructure might need to update their lightning protections. More intense lightning over the oceans could also produce louder booms that stress out sea creatures already harried by human noise pollution.
But it’s not time to start implementing new lightning protections just yet, according to Vernon Cooray, a lightning physicist with Uppsala University in Sweden who was not involved in the study. Cooray said that a spark of a few centimeters interacts with water very differently than a spark of several hundred meters.
“The methods are sound, and the conclusions made about the laboratory discharges are correct,” he said. “Unfortunately, the results cannot be extended to lightning.”
Williams also advised caution about applying the lab results to real-world lightning, which is not only much longer but at least 100 times more intense. Even so, he considers the new research to be valuable.
“It’s an important contribution whenever you have results in the lab where you can measure things that shed important light on large-scale phenomena,” he said. “A simple experiment goes a long way towards provoking ideas and provoking further work.”
—Rachel Fritts (@rachel_fritts), Science Writer
Fritts, R. (2021), More acidic water might supercharge lightning, Eos, 102, https://doi.org/10.1029/2021EO154061. Published on 01 February 2021.
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