There has been some discussion about a paper in Nature Climate Change by Gleckler et al that says they detect “a positive identification (at the 1% level) of an anthropogenic fingerprint in the observed upper-ocean temperature changes, thereby substantially strengthening existing detection and attribution evidence.”
What they’ve done is collect datasets on volume-averaged temperatures for the upper 700 metres of the ocean.
But Yeager and Large, writing in the Journal of Climate, looking at the same layer of ocean, come to a different view. They conclude that it is natural variability, rather than long-term climate change that dominates the sea surface temperature and heat flux changes over the 23 years period (1984 – 2006). They say the increase in sea surface temperatures is not driven by radiative forcing. It’s a good example of how two groups of scientists can look at the same data and come to differing conclusions. Guess which paper the media picked up?
Whilst the IPCC AR4 report says that between 1961 – 2003 the upper 700 metres has increased in temperature by 0.1 deg C, some researchers think that that estimate is an artifact of too much interpolation of sparse data (Harrison and Carson 2007). Their analysis found no significant temperature trends over the past 50 years at the 90% level, although this is a minority opinion.
The interesting thing about Gleckler et al is that their unambiguous detection of a human fingerprint in ocean warming comes from what they say are “results from a large multimodel archive of externally forced and unforced simulations.” To you and me this means with and without anthropogenic carbon dioxide. What they have done is to look at the average of a variety of computer models.