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The warming of Earth is primarily due to accumulation of heat-trapping greenhouse gases, and more than 90 percent of this trapped heat is absorbed by the oceans. As this heat is absorbed, ocean temperatures rise and water expands. This thermal expansion contributes to an increase in global sea level. Temperature measurements of the sea surface, taken by ships, satellites and drifting sensors, along with subsurface measurements and observations of global sea-level rise, have shown that the warming of the upper ocean caused sea level to rise due to thermal expansion in the 20th century. Using measurements from Argo profiling floats, we know this warming has continued, causing roughly one-third of the global sea-level rise observed by satellite altimeters since 2004.