UPDATE: I forgot to note that the data in Figure 1 have been zeroed at the year 2003. That was done to simplify the illustration.
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The National Oceanographic Data Center (NODC) recently updated their ocean heat content and vertically averaged temperature data for the oceans to depths of 2000 meters. See the NODC data webpage here. Alarmists are having a grand time trying to scare their readers with their chicken-little end-is-near proclamations. Example: see the post titled “The oceans are warming so fast, they keep breaking scientists’ charts” at SkepticalScience here and The Guardian here. Also see Joe Romm’s post ‘Hottest Year’ Story Obscures Bigger News: Ocean Warming Now Off The Charts at ClimateProgress.
Of course, the alarmists present the ocean heat content data, not the vertically averaged temperature data. Why? The oceans have an extremely large heat capacity, so a very slight increase in the temperature of the oceans to depths of 2000 meters represents a very large uptake of heat when placed in terms of 10^22 Joules…the units used by the NODC. So to counter the alarmists, we present the NODC data in terms of deg C (data here), because people are more familiar with temperature. We also break the data down into basins and subsets to show that the warming rates are not uniform, which is tough to explain with greenhouse gas-driven human-induced global warming. So here’s a general introductory discussion of that NODC temperature data to depths of 2000 meters.
Reasonably complete temperature samples of all the ice-free oceans to the depths of 2000 meters (about 6600 feet or about 1.25 miles) have only been available for the past decade or so. Those new sensors were deployed as part of the ARGO program in the early 2000s and did not have complete coverage of the oceans until about 2003. The U.S. National Oceanographic Data Center (NODC) uses those temperature samples for a number of datasets, including their vertically averaged temperature data for the depths of 0 to 2000 meters.
Before the early 2000s, even the IPCC calls into question the usefulness of the sparse temperature measurements of the deep ocean. They note that before ARGO the data cannot be used for attribution studies. In other words, because the data are so sparse, they cannot be used to determine the cause of the warming. Also see the post here. It shows how sparse the pre-ARGO data are.
As shown in Figure 1, the ARGO-era temperature data for those depths show the South Atlantic and Indian Oceans have warmed, while the North Atlantic and the largest ocean on our planet, the Pacific, show very little warming over the past 12 years.
The pie chart in Figure 2 helps to put that in perspective. It illustrates the surface areas of the Indian, South Atlantic, North Atlantic and Pacific as percentages of their total surface area. (Source of the surface areas is here.) The North Atlantic and Pacific Oceans cover almost two-thirds of those oceans and they have warmed very little in 12 years to depths of about 2 kilometers (1.25 miles). Now look again at the graph in Figure 1, this time concentrating on the scale of the vertical axis (y-axis) and on the listed warming rates. For the South Atlantic and Indian Oceans, the warming rates measured in one-hundredths of a deg C/decade, while for the North Atlantic and Pacific, the trends are in one-thousandths of a deg C/decade.
Something else to consider: the raw ARGO-based temperature data don’t show that much warming. The data have to be adjusted to show those warming rates.
The other problem: manmade greenhouse gases are said to be well-mixed, meaning they’re spread pretty evenly above the Earth’s surface. It’s difficult at best, therefore, to imagine how manmade greenhouse gases could be warming one-third of the oceans to depths of more than a mile but not the other two-thirds.
The other problem: I had explained the difference in the warming rates between the Indian and Pacific Oceans a number of years ago. See the discussion of Figures 19 and 20 and Animations 1 and 2 in the post Is Ocean Heat Content Data All It’s Stacked Up To Be? But because manmade greenhouse gases are said to be evenly mixed, the multi-model mean of the climate models used by the IPCC (for attribution studies and projections of future climate) show a relatively uniform warming of the oceans. Yet in the real world that is not the case. See the illustration here from Durach et al. (2014) Quantifying underestimates of long-term upper-ocean warming. The multi-model mean basically represent how the oceans should have warmed if they were warmed by manmade greenhouse gases. It’s difficult at best, therefore, to imagine how climate modelers will attempt to explain how manmade greenhouse gases could be warming one-third of the oceans to depths of more than a mile but not the other two-thirds when their models show a more uniform warming.
For more info on the problems with ocean heat content data see the post Is Ocean Heat Content Data All It’s Stacked Up to Be?