Steric height since 2005
Key takeaways
- Warming of the upper 2000 m has raised sea level by about … mm since 2005.
- The ocean absorbs about 90 percent of the extra heat trapped by greenhouse gases.
- Thermal expansion accounts for roughly 40 percent of the rise we see today.
What is steric height?
Sea level rises not only when water is added but also when existing water expands. Warm water takes up more space than cold water, and changes in saltiness affect volume too. These changes are called thermosteric (temperature) and halosteric (salinity) changes. Together they make up steric height.
What are we looking at?
A global array of nearly 4,000 Argo floats drifts through the ocean, diving to 2000 m and surfacing every ten days to report temperature and salinity profiles. NOAA's National Centers for Environmental Information combine these with ship and mooring data to compute how much the upper 2000 m has expanded. The chart shows the change since early 2005, when Argo reached near global coverage.
Why do we care?
Steric height is a direct measure of the heat the ocean is storing. Because the ocean is so large and mixes so slowly, this heat keeps working its way to depth for centuries, which is one reason sea level will keep rising long after emissions fall.
Data: NOAA NCEI global steric sea level, 0 to 2000 m. Data files: ncei.noaa.gov.