What was done
Working with plant macrofossil, peat humification, and testate amoebae data, which they obtained from cores extracted from an ombrotrophic bog (Temple Hill Moss in southeast Scotland), the authors reconstructed a proxy climate record spanning the last 7500 years.

What was learned
Langdon et al. report that the plant macrofossil detrended correspondence analysis (DCA) and colorimetric humification data produced a millennial-scale periodicity of 1100 years, noting that "the only other peat-based palaeoclimatic reconstruction of similar length, Walton Moss (Hughes et al., 2000), also displayed an 1100-year cycle derived from the plant macrofossil DCA reconstruction." In terms of the last two millennia of the 7500-year record, they indicate that coming out of what we know as the Roman Warm Period, there was a "wet shift at around cal. 1450-1350 BP at Temple Hill Moss [that] has also been identified in other peat-based records from northern England, including Walton Moss, as well as from three out of six other sites studied in Scotland (Langdon, 1999)." Of this period they additionally note that "Blackford and Chambers (1991) also provided evidence for a Dark Age (1400 BP) climatic deterioration from five sites in a transect from western Ireland to North Yorkshire," and that "one of the ice rafted debris (IRD) events described by Bond et al. (1997) occurred at ca 1400 BP." Last of all, they state that their data provide evidence "for a drier/warmer phase between ca cal. 1000-800 BP, and a climatic deterioration between ca cal. 250-150 BP, which may relate to phases of warmer and then cooler climates such as the Medieval Warm Period and Little Ice Age, respectively."

What it means
The results of Langdon et al.'s work add to the growing body of evidence supporting the existence of a millennial-scale cycling of earth's climate that results in alternating phases of several-century-long periods of warmer and cooler temperatures; and the implication of this finding is that the global warming of the past century or more was simply the most recent transition stage of this cycle, which brought the planet out of the Little Ice Age and into the Current Warm Period, independently of the concomitant coincidental increase in the air's CO2 content.

References
Blackford, J.J. and Chambers, F.M. 1991. Proxy records of climate from blanket mires: Evidence for a dark age (1400 BP) climatic deterioration in the British Isles. The Holocene 1: 63-67.

Bond, G., Showers, W., Cheseby, M., Lotti, R., Almasi, P., de Menocal, P., Priore, P., Cullen, H., Hajdas, I. and Bonani, G. 1997. A pervasive millennial-scale cycle in North Atlantic Holocene and glacial climates. Science 278: 1257-1266.

Hughes, P.D.M., Mauquoy, D., Barber, K.E. and Langdon, P.G. 2000. Mire development pathways and palaeoclimatic records from a full Holocene peat archive at Walton Moss, Cumbria, England. The Holocene 10: 465-479.

Langdon, P.G. 1999. Reconstructing Holocene Climate Change in Scotland Utilizing Peat Stratigraphy and Tephrochronology. Ph.D. Thesis, University of Southampton.