Here’s the reference:
Richey, J.N., Poore, R.Z., Flower, B.P. and Quinn, T.M. 2007. 1400 yr multiproxy record of climate variability from the northern Gulf of Mexico. Geology 35: 423-426.
And what was learned:
Solid empirical evidence continues to accumulate, demonstrating that the Medieval Warm Period (MWP) was an interval of elevated global temperatures that were equally as warm as, or even warmer than, those of the Current Warm Period, and that the MWP’s elevated warmth was likely solar-induced, which suggests that the Current Warm Period may well be deriving its warmth from the same source, as it is likely nothing more than the most recent manifestation of the warm node of this ever-recurring climate cycle.
