The oceans slow the rate of climate change by storing large amounts of heat and carbon dioxide: more than 93% of the extra heat energy stored by the climate system over the last 50 years is found in the ocean, and the oceans absorb about 30% of human carbon dioxide emissions. These services come at a cost, in the form of sea level rise through thermal expansion and ocean acidification. Ocean observations provide compelling evidence that the oceans have changed in recent decades. The oceans have warmed, become more acidic, and regional changes in salinity provide evidence of changes in evaporation and precipitation over the ocean.

Global mean sea level has risen by 0.19 [0.17 to 0.21] m over the period 1901−2010 and there is medium confidence that the current centennial rate of global mean sea level rise is high in the context of centennial-scale variations over the last two millennia. There is high confidence that observed changes in the ocean and sea level reflect a human influence. Climate model projections indicate that the ocean will continue to warm and sea level will continue to rise during the 21st century. The rate of sea level rise will very likely exceed that observed since the 1970’s due to increased ocean warming and loss of mass from glaciers and ice sheets.

It is virtually certain that global mean sea level rise will continue beyond 2100, with sea level rise due to thermal expansion to continue for many centuries. Observed and projected changes in the ocean and sea level provide strong support for the AR5 assessment that climate is changing, that humans have contributed substantially to the changes observed, and that higher carbon emissions will mean faster rates of change in the future.