Learning From the Argonauts
The best thing about doing climate science the way I do it is that I can study anything I want, and there is always so much more to learn … in the present instance, there’s another year of Argo data, so I thought I’d take another stroll through the world of Argo. The Argo floats sleep a kilometer down, and then every ten days they dive down another kilometer and slowly rise to the surface, measuring temperature and salinity as they go. Then they drop back down a kilometer, and go back to sleep. So start with, here a movie I made up that lets us go diving with the Argo floats down to 2000 metres and back up again …
Figure 1. Movie of the Argo temperatures at standard layers.
One thing I hadn’t realized was how the western sides of the oceans are generally warmer than the eastern sides. Makes sense, because the wind blows in that direction, piling up the warm surface water in the west, and as a result forcing warm water down to deeper levels … at least that’s how I interpret it. I was also surprised by how deep the warm water goes, it’s 18° or so down a couple hundred metres in many places.
The Argo floats are indeed a marvel, but they do have their limitations. One of the limitations is that there are only about 3,500 of them in the ocean at any one time, and the ocean is a very big place. As a result, I don’t know how much trust we can put in the results … but let’s look at them anyhow.
First off, here’s what’s going on at the surface. The data says that there is a small warming of about a tenth of a degree over the decade. But as with many things in climate, the reality is more complex. Here is a breakdown of the surface temperature into the seasonal and residual components:
Figure 2. Argo Surface Temperatures. Top panel shows raw data. Middle panel shows the average changes (seasonal component), month by month, as an anomaly. The bottom panel shows the raw temperature less the seasonal component, again as an anomaly.
Now, despite the fact that there is a trend visible, as detailed in the bottom of Figure 2, you can see that the temperature dropped from the beginning of the record in January 2005 to about January 2008. Then for two years, the temperature rose rapidly … and dropped again for the next two years, and then rose again to the end of the record.
Because of this variation, I’d say that drawing any conclusions from the apparent tenth of a degree per decade “trend” is very premature. Let me give you another example of this same problem. Figure 3 shows the temperature trends at the surface, in degrees per decade.
Figure 3. Surface temperature trends by area. Dark blue and green show cooling.
Now, there’s a number of interesting things about this map. First, most of the ocean isn’t doing a whole lot, either trivially warming (cyan) or trivially cooling (light green).
Next, there are isolated areas that are significantly cooling—off the southern tip of Africa, near China, down in the Antarctic, and most curiously, the North Atlantic.
Similarly, there are isolated areas of warming—west of australia, off of Japan, west of Panama, east of Argentina, and off the northeast US.
Finally, the tropics by and large is not warming in any significant manner. This is in line with my hypothesis that tropical clouds greatly constrain the temperature variations in the tropics.
Anyhow, that’s what I learned from looking at Argo. I learned once again that linear trends are always deceptive … and a lot besides that. Always more to find out in this field, I guess that’s why they call climate the “settled science” …
My best wishes to all of you, warm oceans and crisp evenings, and time with those you love,
w.
Note from the Author:
The Argo floats are technical marvels. They float around below the surface of the ocean, about a kilometre down, for nine days. On the tenth day, they rise slowly to the surface, sampling the pressure, temperature, and salinity as they go. When they reach the surface, they radio home like ET, transmit the data from the instrumental profiles, and they drop back down into the eternal darkness for another nine days. The first Argo floats were put into the ocean in the year 2000. In 2007, the goal of 3,000 floats was achieved.
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