A new paper has been published in Science, 3rd January, that uses the words ‘natural variability,’ the abstract copied below is self explanatory:
The Spatial Pattern and Mechanisms of Heat Content Change in the North Atlantic
M. Susan Lozier 1, Susan Leadbetter 2, Richard G. Williams 2, Vassil Roussenov 2, Mark S. C. Reed 1, Nathan J. Moore 3
1 Division of Earth and Ocean Sciences, Nicholas School of the Environment and Earth Science, Duke University, Durham, NC 27708, USA.
2 Department of Earth and Ocean Sciences, Liverpool University, Liverpool, L69 3GP U.K.
3 Division of Earth and Ocean Sciences, Nicholas School of the Environment and Earth Science, Duke University, Durham, NC 27708, USA; Current affiliation: Department of Geography, Michigan State University, East Lansing, MI, 48823 USA.
Abstract:
The total heat gained by the North Atlantic Ocean over the past fifty years is equivalent to a basin-wide increase in the flux of heat across the ocean surface of 0.4 ±0.05 Wm-2. We show, however, that this basin has not warmed uniformly: though the tropics and subtropics have warmed, the subpolar ocean has cooled. These regional differences require local surface heat flux changes (±4 Wm-2) much larger than the basin-wide average. Model investigations show that these regional differences can be explained by large-scale, decadal variability in wind and buoyancy forcing, as measured by the North Atlantic Oscillation index. Whether the overall heat gain is due to anthropogenic warming is difficult to confirm, since strong natural variability in this ocean basin is potentially masking such input at the present time.

Jennifer Marohasy BSc PhD has worked in industry and government. She is currently researching a novel technique for long-range weather forecasting funded by the B. Macfie Family Foundation.