Marine energy is one of the most widely available forms of renewable energy; the seas encompass 71% of the Earth's surface, which could theoretically meet all of the world's electricity needs. Researchers and industry developers from all over the world are interested in the promising future of marine energy. Wave, tidal stream, tidal range, ocean thermal, ocean current, run-of-river, and salinity are all examples of marine energy (or ocean energy) that can be harnessed from oceans. Marine energy will help to reduce global carbon emissions. The development of large-scale marine energy projects will have unforeseen environmental consequences, the majority of which have been thoroughly evaluated. Several phenomena, such as salinity gradient (energy derived from the difference in salt concentration between seawater and freshwater), temperature gradient, waves, and ocean currents, can be used to extract energy from the sea. Ocean waves, for example, have enormous promise as a renewable energy source.