The salt water comprising Earth’s oceans is an excellent conductor of electricity. When salty seawater moves through Earth’s naturally occurring magnetic field, it forms tiny electric fields and magnetic fields of its own within the ocean.
This process generates electromagnetic signals, which can be detected by power cables along the ocean floor, sensors on land, and satellites up in space. New satellite missions, such as the European Space Agency’s Swarm (named for the way its three satellites zip around the globe, hovering hundreds of kilometers above Earth’s surface), are able to detect these signals with increasing precision.
Because these electromagnetic signals are known to vary depending on seawater temperature and salinity, scientists think they could be useful for monitoring changes in ocean climate. Using a state-of-the-art model of the Earth’s ecosystems, Saynisch et al. simulated how ocean warming due to climate change over the next 94 years will affect the electromagnetic signals emitted by ocean tides.
During that time period, the electromagnetic signals emitted by the world’s ocean tides will change by very small amounts, the authors found: about 0.3 nanotesla and about 0.000001 volt per kilometer. When examined locally, however, the changes will be much higher. For example, the magnetic field in the northern Atlantic will increase by a full nanotesla.
Overall, ocean warming due to climate change will cause small electromagnetic anomalies, compared to Earth’s background magnetic field, but the anomalies will occur across large areas of the world’s oceans, especially in the Northern Hemisphere. The researchers think these disturbances would be detectable using modern technology and are likely to show up in electromagnetic observations. The study is a promising step toward developing a powerful, precise tool to help monitor Earth’s changing climate. (Geophysical Research Letters, https://doi.org/10.1002/2017GL073683, 2017)
—Sarah Witman, Freelance Writer