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In contrast to ocean circulation signals, ocean tides are already well detectable by electromagnetic measurements. Oceanic electric conductivities from the Coupled Model Intercomparison Project Phase 5 (CMIP5) climate simulations are combined with tidal currents of M2 and O1 to estimate electromagnetic tidal signals and their sensitivity to global warming. Ninety-four years of global warming leads to differences of +/- 0.3 nT in tidal magnetic amplitudes and +/- 0.1 mV/km in the tidal electric amplitudes at sea level. Locally, the climate-induced changes can be much higher, e.g., +1 nT in the North Atlantic. In general, all studied electromagnetic tidal amplitudes show large-scale climate-induced anomalies that are strongest in the Northern Hemisphere and amount to 30% of their actual values. Consequently, changes in oceanic electromagnetic tidal amplitudes should be detectable in electromagnetic records. Electric and magnetic signals, as well as tides of different frequencies, contain complementary regional information.

Plain Language Summary Ocean water is a good conductive medium. Ocean water flow through Earth's ambient magnetic field generates measurable electromagnetic signals. By using state of the art Coupled Model Intercomparison Project Phase 5 climate predictions, climate change-induced variations in seawater electric conductivity are calculated. Since these conductivity variations are slow and hard to separate in electromagnetic observations, the derived electric conductivity is combined with ocean tide velocities. Tides are since long detectable with magnetometer observations. We calculate the respective electromagnetic ocean tidal signals and relate their anomalies to climate change. We conclude that climate impact should be detectable in electromagnetic observations, even from space.