Climate Change of over 20 °C Induced by Continental Movement on a Synchronously Rotating Exoplanet

It is generally believed that the addition of continents cools the climate of an aquaplanet with a similar orbit to Earth; this is because continents have a higher surface albedo than oceans. A similar effect has been shown in climate simulations for exoplanets. Here we demonstrate that the influence of a continent on ocean circulation could have a dominative effect on the climate of a synchronously rotating exoplanet compared with the effect of the surface albedo, especially when the rotation of the exoplanet is relatively slow (e.g., the rotational period is 40 Earth days). The global mean surface temperature could vary by more than 26° C, simply by moving a small continent to a different location. The ocean circulation on a synchronously rotating exoplanet is characterized by a strong westerly jet along the equator and one large gyre in each hemisphere. The surface temperature decreases when the equatorial westerly or the western branch of either of the gyres is blocked by a continent or an island arc chain. However, if the continent blocks the eastern branch of the gyre, the equatorial westerly is strengthened and the climate warms. A large number of potentially habitable exoplanets have been found orbiting around M-dwarfs in a tidally locked manner; our results indicate that their climates, as well as their atmospheric chemistry, may deviate from previous estimates if a small continent, or even an island arc chain, is present.