# Ocean Temperature And Heat Content

**The upper ocean temperature was roughly flat from 1993-1998. Then it increased by about one tenth of a degree in the next five years to 2003, and has been about flat since then.**

Anthony has an interesting post up discussing the latest findings regarding the heat content of the upper ocean. Here’s one of the figures from that post.

*Figure 1. Upper ocean heat content anomaly (OHCA), 0-700 metres, in zeta-joules (10^21 joules). Errors are not specified but are presumably one sigma. SOURCE *

He notes that there has been no significant change in the OHCA in the last decade. It’s a significant piece of information. I still have a problem with the graph, however, which is that the units are meaningless to me. What does a change of 10 zeta-joules mean? So following my usual practice, I converted the graph to a more familiar units, degrees C. Let me explain how I went about that.

To start with, I digitized the data from the graph. Often this is far, far quicker than tracking down the initial dataset, particularly if the graph contains the errors. I work on the Mac, so I use a program called GraphClick, I’m sure the same or better is available on the PC. I measured three series: the data, the plus error, and the minus error. I then put this data into an Excel spreadsheet, available here.

Then all that remained was to convert the change in zeta-joules to the corresponding change in degrees C. The first number I need is the volume of the top 700 metres of the ocean. I have a spreadsheet for this. Interpolated, it says 237,029,703 cubic kilometres. I multiply that by 62/60 to adjust for the density of salt vs. fresh water, and multiply by 10^9 to convert to tonnes. I multiply that by 4.186 mega-joules per tonne per degree C. That tells me that** it takes about a thousand zeta-joules to raise the upper ocean temperature by 1°C**.

Dividing all of the numbers in their chart by that conversion factor gives us their chart, in units of degrees C. Calculations are shown on the spreadsheet.

*Figure 2. Upper ocean heat content anomaly, 0-700 metres, in degrees C. *

I don’t plan to say a whole lot about that, I’ll leave it to the commenters, other than to point out the following facts:

• The temperature was roughly flat from 1993-1998. Then it increased by about one tenth of a degree in the next five years to 2003, and has been about flat since then.

• The claim is made that the average temperature of the entire upper ocean of the planet is currently known to an error (presumably one sigma) of about a hundredth of a degree C.

• I know of no obvious reason for the 0.1°C temperature rise 1998-2003, nor for the basically flat temperatures before and after.

• The huge increase in observations post 2002 from the addition of the Argo floats didn’t reduce the error by a whole lot.