What was done
The authors derived and analyzed ocean temperature trends over the period 1955-2003 at depths ranging from 50 to 1000 meters in order to "test the sensitivity of trends to various data processing methods," utilizing the World Ocean Database 2005 (Boyer et al., 2006), employing the analytical approach of Harrison and Carson (2007), and comparing their results (primarily) with those of Levitus et al. (2005).

What was learned
In terms of Carson and Harrison's analytical procedure, the results indicated, in their words, that "most of the ocean does not have significant 50-year trends at the 90% confidence level (CL)." In fact, they say that "only 30% of the ocean at 50 meters has 90% CL trends, and the percentage decreases significantly with increasing depth." In comparison with prior calculated trends, they also report that the results "can differ substantially, even in the areas with statistically significant trends," noting finally that "trends based on the more interpolated analyses," such as those of Levitus et al. (2005), "show more warming."

What it means
The two researchers conclude, and rightly so, that "ocean heat content integrals and integral trends may be substantially more uncertain than has yet been acknowledged."

References
Boyer, T.P. and Coauthors. 2006. World Ocean Database 2005. NOAA Atlas NESDIS 60, 190 pp.

Harrison, D.E. and Carson, M. 2007. Is the world ocean warming? Upper-ocean temperature trends: 1950-2000. Journal of Physical Oceanography 37: 174-187.

Levitus, S., Antonov, J.I., Boyer, T.P. and Stephens, C. 2005. Warming of the world ocean, 1955-2003. Geophysical Research Letters 32: 10.1029/2004GL021592.