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Carbon dioxide isn’t just a greenhouse gas, warming the planet by trapping heat in the atmosphere. According to the US National Oceanic and Atmospheric Administration, one third of our estimated CO2 emissions end up in the ocean.

This leads to ocean acidification, which is harmful to marine life. But ocean acidification might also trigger another phenomenon: stronger lightning strikes. Bet you didn’t see that one coming.

On the one hand, the ocean absorbing CO2 might seem like a good thing because there’s less of it in the atmosphere to warm the planet. But on the other hand, CO2 that dissolves in the ocean becomes carbonic acid. And the more CO2 the ocean absorbs, the more acidic the water becomes.

This is bad news for corals and other shell-forming marine organisms, because they make their shells from minerals like calcium carbonate, which dissolve in acidic water. But that’s not the only effect decreasing the pH of the ocean might have. We think of pH as a measure of acidity, and that’s true.

But on a molecular scale, pH is actually a measure of the concentration of hydrogen ions in a solution. The more hydrogen ions, the more acidic the solution is. In the case of CO2, the carbonic acid splits apart into positively charged hydrogen ions and negatively charged bicarbonate.

The presence of those charged ions means the solution can also carry an electrical charge. A higher acidity, or a lower number on the pH scale, means more hydrogen ions in the solution, and more potential to conduct electricity. And that’s a big deal, because the ocean is getting more acidic.

Due to climate change, seawater has experienced a 0.1 unit drop in pH. Which seems tiny, but the pH scale is logarithmic. A pH of 6 is ten times more acidic than a pH of 7.

So that change of 0.1 in the oceans corresponds to a 30% increase in acidity! So if climate change is potentially affecting the electrical conductivity of the ocean, could it affect lightning? This led a group of scientists to look into the idea, publishing two papers on the subject in 2020.

Surprisingly, we don’t know a lot about what happens when lightning hits the ocean, even less than we know about lightning strikes in general, because almost all lightning strikes happen on land. For something so big, covering nearly two-thirds of the Earth, oceans are only struck by about 10% of all the lightning that occurs. We used to assume that all surfaces act as perfect conductors, whether that surface is rocks, soil, or water.

But while this assumption makes it easier to do calculations, it probably doesn’t reflect reality perfectly. In fact, models show that when lightning does hit the ocean, it could be more intense than on land, probably because salt water is a better conductor. So to test whether lightning could intensify as the ocean acidifies, the researchers carried out a simple experiment.

They filled a beaker with seawater and placed two electrodes in the water, about two centimeters apart. Then they ran power through the electrodes, forming sparks between them. Next, they changed the seawater's pH in two different ways.

First, they added hydrochloric acid directly to the water. This is a good way to change the pH of the solution, but it doesn’t reflect the real-world process of ocean acidification very well. Second, they decreased the pH by bubbling carbon dioxide into the water, which is pretty close to how ocean acidification actually works.

And they found that as the water got more acidic, the spark’s intensity did increase. The bubbling technique, which most closely replicates ocean acidification, made the spark twice as intense as the other method. That means ocean acidification could be making lightning stronger.

In fact, the researchers claim that if ocean pH keeps decreasing according to the worst case predictions, where CO2 emissions keep increasing unchecked, the intensity of ocean lightning strikes could increase by 30% by the end of this century. This is a definite concern for ships, oil rigs, and other ocean infrastructure. All of these structures already have some form of lightning protection.

But if lightning does get more intense with climate change, these protections might need an upgrade. But it isn’t just human-made structures that might be affected. Lightning strikes aren’t just shocking; they’re also loud.

So if lightning strikes are getting stronger, animals that use sound to navigate, like whales and dolphins, might have a harder time. But maybe we shouldn’t worry too much yet. Some researchers caution that while this study’s method does what it’s supposed to do, measuring a spark in a beaker of water might not be directly applicable to storms over the ocean.

Lightning produces very large sparks, up to several hundred meters long. Sparks this big might behave very differently from small sparks generated in a controlled environment like a laboratory. Lightning is also a hundred times more intense than the sparks these researchers produced.

So, comparing the two is a bit of a stretch. But these studies are laying the groundwork for future experiments. Which hopefully will spark more research.

Thanks for watching this episode of SciShow. Before you go, I just want to remind you that time is running out to grab. SciShow Space’s Pin of the Month for June!

It’s this charming little drawing of Surveyor 1, the probe that heralded the Apollo missions to the Moon. And you can only pre-order it until midnight, June 30th. After that, we’ll stop taking any more orders and start working on the next pin.

You can check it out at the link in the description, and stay tuned for next month’s pin, too! [♪ OUTRO].