Also see Gerard McCarthy's replies to my query to him via Twitter - here and here and here.
Sou 2 June 2015
There was a new paper that came out this week in Nature, which had a bit of coverage around the traps. Deniers rather liked it not so much because of what was in the paper itself, but because of what was in the press release.
The paper was by a team from the University of Southampton, led by Dr. Gerard D. McCarthy. The paper was about the Atlantic Multidecadal Oscillation or AMO and ocean heat transport, and related.
The AMO is used to indicate changes in sea surface temperature in the North Atlantic. It is of such long duration that there aren't instrumental records going back far enough to show multiple repeating patterns. It's probably not a regular cycle with a fixed period. Estimates seem to place the latest period at around 70 years (from the beginning of a warm phase in the 1920s to the end of a cool phase in the 1990s - see here). The latest IPCC report had this to say about it (page TS-25):
A number of studies have investigated the effects of the Atlantic Multidecadal Oscillation (AMO) on global mean surface temperature. While some studies find a significant role for the AMO in driving multi-decadal variability in GMST, the AMO exhibited little trend over the period 1951-2010 on which these assessments are based, and the AMO is assessed with high confidence to have made little contribution to the GMST trend between 1951 and 2010 (considerably less than 0.1°C). {2.4, 9.8.1, 10.3; FAQ 9.1}.From the above paragraph I take it that the nature of the AMO is not all that well agreed upon - by some at least.