Thermal expansion happens when water gets warmer, which causes the volume of the water to increase. About half of the measured global sea level rise on Earth is from warming waters and thermal expansion. The ocean absorbs greenhouse gases and stores heat until the temperature rises. As a result, the expansion of water causes the sea level to rise. The average global sea surface temperature has increased about 1.5oF since 1901, an average rate of 0.13oF per decade.Thermal ocean expansion is one of the major contributors to sea level changes during the 20th and 21st centuries. Salinity changes within the ocean also have a significant impact on the local density and thus local sea level, but have little effect on global average sea level change.