Scientists generally expect fish on the high seas to be less affected by global warming than coastal and inland fisheries. The year-to-year variations in climate conditions appear to be much greater than the change expected from greenhouse gases over the next century. Nevertheless, oceanographers are currently unable to rule out the possibility that global warming may exacerbate El Niņo 
and other causes of fluctuation.
Warmer temperatures are likely to enhance fishing in many areas. Overall biological activity is greater at higher temperatures, more food is available, fish grow faster, and they reproduce at a younger age. The expected increase in fisheries from warmer temperatures may be partly offset, however, by a decline in the upward flow of deep ocean water to the surface (upwelling). These upward flows bring nutrients to the upper layers of the ocean, increasing the growth of the aquatic plants that form the base of the marine food chain.