The oceans have a mass 1000 times that of the atmosphere. So if they were predicting 2C increase in the heat of the atmosphere wouldn't that be .002 deg Celsius in the ocean? Can you even measure that give the vastness of the ocean?
So when I said that the ocean has 1000x the mass of the atmosphere, I did the math earlier to get the total mass of both. That is a different calculation than the below per unit of volume measurement.
Sea water has a mass of ~1000kg/m^3. Sea level air has a mass of 1.2kg/m^3. How does it only take 4 times as much energy to heat up a cubic meter of seawater than a cubic meter of air? Wouldn't it be ~820 times as much?