A new study by NASA (National Aeronautics and Space Administration) scientists has found that the contribution to sea level rise is only from the upper half (0-2,000m) of the ocean and the ocean below this depth has no role to play in sea level rise. This conclusion was arrived at by subtracting the sea level changes occurring at 0 to 2,000 metres depth from that of the entire water column. The subtraction provided only zero values.

Satellite altimetry

The total contribution to sea level rise from the entire water column was determined using satellite altimetry (measuring height) using NASA’s Jason-1 and Jason-2 satellites. Satellite altimetry measured the changes in sea level and annual mean sea level increases were obtained for the study period (2005 to 2013).

From the values obtained by this method the contributions due to thermal expansion as measured by the Argo array of floats were subtracted. Water expands as it gets warmer. The sea level is rising partly because of this expansion.

Argo array

Scientists have been recording the temperature and sea levels of the top half of the ocean directly since 2005, using a network of 3,000 floating temperature probes called the Argo array of floats. The Argo floats are used to measure sea level variations due to thermal expansion (steric sea level) of the ocean in the 0-2,000m ocean layer.

To subtract the sea level variations due to ice berg and glacier melt data from the GRACE (Gravity Recovery and Climate Experiment) of NASA were used.

These data also pertain to the upper (0-2000m) half of the ocean.

The two subtractions resulted in zero values indicating that the lower half (2,000 m to bottom) has no role to play in sea level rise due to both climate change derived melting icebergs, glaciers and thermal expansion due to rising temperatures (ocean warming).

The study, whose first author is William Llovell of NASA, was published recently in a paper in Nature Climate Change.