Background
According to Banks and Wood (2002), the southern boundary of the Indian Ocean is one of six geographical regions identified as having a particularly high signal-to-noise ratio for detecting climate change.  In a study of observations made in the south Indian Ocean subtropical gyre, Bindoff and McDougall (2000) found that prior to 1987 the thermocline waters of the Indian Ocean at 32°S had cooled and freshened on isopycnals for about two and a half decades.  These observed changes in the Indian Ocean Subantarctic Mode Water have been shown to be similar to changes simulated in the Third Hadley Centre coupled Ocean-Atmosphere General Circulation Model when driven by anthropogenic forcing (Banks et al., 2000), which cooling and freshening have been characterized by Banks and Bindoff (2003) as a fingerprint of anthropogenic forcing.

What was done
In March-April of 2002, the authors of the present study visited the southern Indian Ocean to measure the meriodional overturning circulation along the 32nd Parallel between Africa and Australia.  Then, using data from four prior excursions across this boundary region (in 1936, 1965, 1987 and 1995), the authors quantified and examined the change in heat and salt content of the thermocline to shed some light on whether or not the 1987 cooling and freshening was indeed the result of anthropogenic forcing.

What was learned
McDonagh et al.'s analyses revealed there was a significant change in the properties of the thermocline across the entire distance of the 32nd parallel under study between 1987 and 2002 that effectively reversed the cooling and freshening trend that was previously characterized as a fingerprint of global warming.  What is more, all indications suggest that the present state of the thermocline is no different from what it was back in 1936 (Bryden et al., 2003).

What it means
The reversal of trends in the southern Indian Ocean thermocline discovered in this study to have occurred between 1987 and 2002 demonstrates that we still have much to learn about the earth-ocean-atmosphere system; and it deals a significant blow to those who earlier claimed that the pre-1987 cooling and freshening were due to global warming.  Clearly, far too many people have "jumped the gun" in saying they see fingerprints of anthropogenic-induced global warming in different geophysical data sets when other explanations or additional newer data subsequently prove them to have been wrong, as in this case.

References
Banks, H.T. and Bindoff, N.L.  2003.  Comparison of observed temperature and salinity changes in the Indo-Pacific with results from the coupled climate model HadCM3: Processes and mechanisms.  Journal of Climate 16: 156-166.

Banks, H. and Wood, R.  2002.  Where to look for anthropogenic climate change in the ocean.  Journal of Climate 15: 879-891.

Banks, H.T., Wood, R.A., Johns, T.C. and Jones, G.S.  2000.  Are observed decadal changes in intermediate water a signature of anthropogenic climate change?  Geophysical Research Letters 27: 2961-2964.

Bindoff, N.L. and McDougall, T.J.  2000.  Decadal changes along an Indian Ocean section at 32°S and their interpretation.  Journal of Physical Oceanography 30: 1207-1222.

Bryden, H.L., McDonagh, E.L. and King, B.A.  2003.  Changes in ocean water mass properties: Oscillations or trends?  Science 300: 2086-2088.