Salinity gradient power (or blue energy) is a renewable energy source mentioned in the literature since the 1950s. It refers to the production of electricity by mixing of two solutions with different salt concentrations, for example river and sea water. The global potential of salinity power has been estimated in the 1970s as substantial, but the state of membrane technology at that time - crucial for energy recovery - did not permit the practical use of this resource. More recently, the interest in salinity power has been growing because of the need for carbon neutral, renewable sources of electricity. This study aims to assess the potential of salinity-gradient power for reducing emissions of CO2 and non-CO2 greenhouse gases. First, we discuss the global technical potential for blue energy, i.e. the maximum amount of energy that could be retrieved at the current state of technology. We focus on rivers as source of fresh water and seas as source of saline water. The analysis is based on global datasets of annual river discharges for more than 5000 world rivers. The resulting estimates of global and regional potentials for salinity gradient power are used to estimate the potential for reducing greenhouse gases, assuming that salinity power would reduce the need for fossil fuels. The results are shown for global totals, regional totals and selected rivers.