Global warming alarmists have been hard pressed to explain the lack of warming over the past 15 years or so, even though the carbon dioxide content of the atmosphere has been steadily rising. One of their contentions is that the heat is hiding in the deep oceans. That heat must be a wily beast because it is very good at hiding. This subject continues to be very controversial and exacerbated by the fact that we really did not have good data on deep ocean temperatures until very recently.
Prior to 1969, there was almost no data. Starting in 1969, the majority of the temperature measurements at depth were taken by Expendable BathyThermograph (XBT) devices. These were instruments dropped over the side of a ship, attached by wire, and with an alleged known sinking rate. They would record temperatures as they sank. The obvious problem with this method, is that XBTs were used only where ships traveled, so there are no measurements for most of the ocean.
Beginning in the 1990s, a new system, ARGO, was developed as an international project. The ARGO system consists of a series of floats that would rise and fall measuring temperatures and salinities as they went. The data are transmitted to satellites. By about 2003, the ARGO system provided relatively good coverage and there are now more than 3,000 ARGO devices throughout the world’s oceans.
To begin analysis of the mystery, I present a graph of ocean temperatures prepared by Bob Tisdale, proprietor of Climate Observations, and a specialist in matters of ocean temperature and heat content, as well as the El Nino oscillations that drive our weather. According to this graph, there has not been much change in global ocean temperature since 1955 when the graph starts.
The graph above shows a rough average of global ocean heat content. No apparent missing heat there, but individual ocean basins and hemispheres show a more complicated story.
Switching now to just the ARGO data, we see that the heat may be hiding in the Southern Hemisphere. How could well-mixed carbon dioxide in the atmosphere accomplish that trick, especially since most carbon dioxide emissions come from the Northern Hemisphere? As we will see below it might depend on who is presenting the data. The graph below is a version using “corrected” data from the U.S. National Oceanographic Data Center (NODC).
ARGO data show warming in the Indian Ocean, but cooling of both the north Pacific and north Atlantic oceans.
Just where the heat is and how much there is seems to depend on who is doing the modeling. The U.S. National Oceanographic Data Center ARGO data shows a slight rise in global ocean heat content, while the British Met Office, presumably using the same data shows a slight decline in global ocean heat content.
As far as I can tell, the question of whether or not there is “missing heat” and if so, where it is hiding remains an open question. Solving the mystery of ocean heat content is more complicated that just measuring temperatures. It may depend on basin configuration and the effects of solar-driven oscillations such as El Nino and the Indian Monsoons. Is carbon dioxide induced heating of the deep ocean hiding just in computer models rather than in Nature?
One other complication: The ARGO buoys have an uncertainty range of about 0.1̊C. As you can see on the last graph, that uncertainty range could encompass almost the entire range of alleged variation in deep ocean temperature.