Warmer Waters during Medieval Warm Period

Cunningham et al studied ten proxy sea surface temperature (SST) records as reported by their paper in The Holocene. CO2 science say that their graphical representations clearly indicate that the peak warmth of the Medieval Warm period is warmer than the Current Warm Period

CO2 Science:

What was done
Using ten proxy sea surface temperature (SST) records - six from the Norwegian Margin, three from the North Icelandic Shelf and one from the Scottish Margin - Cunningham et al. prepared a 1,000-year SST record spanning the period from AD 1000 to 2000, which revealed, in their words, that "the 'Medieval Climate Anomaly' warming was most pronounced before AD 1200, with a long-term cooling trend apparent after AD 1250." And what did the new record reveal about the uniqueness - or not! - of the region's late-20th-century Current Warm Period?

What was learned
The twenty researchers report that "in recent decades temperatures have been similar to those inferred for the 'Medieval Climate Anomaly'." However, their graphical representations (three versions of them) of the one-thousand-year period clearly indicate that the peak warmth of the Current Warm Period has actually been a couple tenths of a degree C less than that of the earlier Medieval Warm Period.

The Abstract:

We undertake the first comprehensive effort to integrate North Atlantic marine climate records for the last millennium, highlighting some key components common within this system at a range of temporal and spatial scales. In such an approach, careful consideration needs to be given to the complexities inherent to the marine system. Composites therefore need to be hydrographically constrained and sensitive to both surface water mass variability and three-dimensional ocean dynamics. This study focuses on the northeast (NE) North Atlantic Ocean, particularly sites influenced by the North Atlantic Current. A composite plus regression approach is used to create an inter-regional NE North Atlantic reconstruction of sea surface temperature (SST) for the last 1000 years. We highlight the loss of spatial information associated with large-scale composite reconstructions of the marine environment. Regional reconstructions of SSTs off the Norwegian and Icelandic margins are presented, along with a larger-scale reconstruction spanning the NE North Atlantic. The latter indicates that the ‘Medieval Climate Anomaly’ warming was most pronounced before AD 1200, with a long-term cooling trend apparent after AD 1250. This trend persisted until the early 20th century, while in recent decades temperatures have been similar to those inferred for the ‘Medieval Climate Anomaly’. The reconstructions are consistent with other independent records of sea-surface and surface air temperatures from the region, indicating that they are adequately capturing the climate dynamics of the last millennium. Consequently, this method could potentially be used to develop large-scale reconstructions of SSTs for other hydrographically constrained regions.

Cunningham, L.K., Austin, W.E.N., Knudsen, K.L., Eiriksson, J., Scourse, J.D., Wannamaker Jr., A.D., Butler, P.G., Cage, A.G., Richter, T., Husum, K., Hald, M., Andersson, C., Zorita, E., Linderholm, H.W., Gunnarson, B.E., Sicre, M.-A., Sejrup, H.P., Jiang, H. and Wilson, R.J.S. 2013. Reconstructions of surface ocean conditions from the northeast Atlantic and Nordic seas during the last millennium. The Holocene 23: 921-935.