>Ocean Areas in IPCC TAR Figure 2.9(c) That Cooled From 1946 to 1975


Of all the graphs contained in the Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report (TAR), I’ve always found the third cell of the IPCC TAR Figure 2.9 the most interesting. Refer to Figure 1.

Figure 1

Quoting text from the IPCC TAR illustration, it identifies land and sea surface areas that “show widespread cooling in the Northern Hemisphere relative to much of the Southern”. Refer to:

There were few if any explanations provided for the SST cooling during this period. Thermohaline Circulation (THC) and Meridional Overturning Circulation (MOC) were not discussed. While the effects for many areas are the result of THC/MOC, climatologists try to match the drop in temperature with aerosols.


Figure 2 shows nine areas blocked off for a second look.
Figure 2

The coordinates used were:
Area A = 40 to 60N, 120W to 180
Area B = 30 to 60N, 75W to 10E
Area C = 25 to 45N, 145E to 180
Area D = 10 to 40N, 100 to 135W
Area E = 5 to 30N, 15 to 45W
Area F = 15S to 15N, 135 to 170W
Area G = 10 to 30S, 100 to 145W
Area H = 15 to 55S, 70 to 80W
Area I = 10 to 40S, 80 to 110E

For those interested in the SSTs for those areas, I’ve prepared Figure 3. The Equatorial East Pacific (Area F) is logically warmest, and the Northeast Pacific (Area A) is coolest.
Figure 3

Figure 4 is a colorful spaghetti graph of the areas that cooled from 1946 to 1975 according to the IPCC illustration. It covers the period of January 1854 to May 2008. I provided the two vertical black lines to ballpark 1946 and 1975.
Figure 4

In Figure 5, the Northeast Pacific (Area A, Blue), the Mid-Latitude North Atlantic (Area B, Red), and the Mid-Latitude Northwest Pacific (Area C, Green) SST anomalies are shown from January 1854 to May 2008. All three signals have THC/MOC signatures. From 1885 to 1910, the Northeast Pacific SST plummeted more than 1.2 deg C, and from 1946 to 1975, it dropped more than 0.5 deg C. The other two variables dropped but to lesser amounts over both periods.
Figure 5

Figure 6 shows the SST anomalies for the Low Latitude Northeast Pacific (Area D, Purple), Low Latitude Northeast Atlantic (Area E, Maroon), and the Equatorial East Pacific (Area F, Bronze). Consistent with upwelling areas, the Low Latitude Northeast Pacific and the Low Latitude Northeast Atlantic also show signs of THC/MOC. The Equatorial East Pacific shows a negative trend from 1854 to the mid-1930s. All three data sets illustrate drops in temperature from 1946 to 1975, but the Low Latitude Northeast Atlantic and Pacific are on the order of 0.2 deg C, while the Equatorial East Pacific dropped only about 0.05 deg C.
Figure 6

The final illustration, Figure 7, shows the SST anomalies from January 1854 to May 2008 for the Low Latitude Southeast Pacific (Area G, Yellow), the Southwest Coast of South America (Area H, Orange), and the Mid Latitude Southeast Indian Ocean (Area I, Black). Apparently, I misread the indicators of cooling in the Southeast Indian Ocean, since its temperature rose from 1946 to 1975. The other two data sets did cool from 1946 to 1975: the Low Latitude Southeast Pacific around 0.1 deg C, and the Southwest Coast of South America approximately 0.3 deg C. But prior to that, from 1890 to 1900, the Southwest Coast of South America dropped more than 0.8 deg C. Over the same period, the Low Latitude Southeast Pacific, nearby, dropped almost 0.3 deg C, in what appears to be a dampened response to the THC/MOC upwelling off the South American Coast.
Figure 7

In the second part of this series, I’ll take a look at the areas that did not cool.


Sea Surface Temperature Data is Smith and Reynolds Extended Reconstructed SST (ERSST.v2) available through the NOAA National Operational Model Archive & Distribution System (NOMADS).

About Bob Tisdale

Research interest: the long-term aftereffects of El Niño and La Nina events on global sea surface temperature and ocean heat content. Author of the ebook Who Turned on the Heat? and regular contributor at WattsUpWithThat.
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