Because the sea absorbs 90% of the heat caused by human activity, its warmth is a central concern in climate science. The new work suggests that shallow layers bear the brunt of ocean warming. Scientists compared temperature data, satellite measurements of sea level, and results from climate models.
Both the papers appear in the journal Nature Climate Change. Specifically in the Southern Hemisphere where fewer measurements have been made, a team of researchers from the Lawrence Livermore National Laboratory in California investigated long-term warming in the top 700m of the ocean.
They wanted to compare published warming rates, based on the sparse temperature data recorded directly from southern waters, with what could be predicted based on more detailed observations in the north, together with climate models and precise sea-level measurements. Sea levels across the planet are accurately assessed by satellites, which bounce radio waves off the ocean surface. And sea level changes are closely related to ocean temperature, because the water expands as it warms up.