Background
The author writes that "information produced by climate modeling has become progressively more important to understand past climate changes as well as to predict future climates." However, Park rightly states that "to evaluate the reliability of such climate model results, quantitative paleoclimate data are essential."

What was done
In a study designed to obtain such "quantitative paleoclimate data" for a part of the world that has not been intensively studied in this regard, the Korean scientist used modern surface pollen samples from the mountains along the east coast of Korea to derive pollen-temperature transfer functions, which were tested for robustness via detrended correspondence analysis and detrended canonical correspondence analysis, after which the best of these transfer functions was applied to the five fossil pollen records of Jo (1979), Chang and Kim (1982), Chang et al. (1987), Fuiki and Yasuda (2004) and Yoon et al. (2008), which were derived from four coastal lagoons of Korea's east coast plus one high-altitude peat bog.

What was learned
Focusing on the late Holocene, and using results obtained from all five pollen data sets, Park found that "the 'Medieval Warm Period', 'Little Ice Age' and 'Migration Period' were clearly shown," the former of which is identified as occurring between AD 700 and 1200, the next of which is identified as occurring between AD 1200 and 1700, and the latter of which is identified as occurring between AD 350 and 700. This earliest period is also commonly referred to as the Dark Ages Cold Period; but it is sometimes described as the Migration Period, as Park reports that it was a time "when people migrated southward in Europe because of deteriorating environmental conditions." Also of significance is the fact that the graphical representation of Park's temperature reconstruction indicates that the peak temperature of the Medieval Warm Period was only slightly lower (by about 0.18°C) than the peak temperature of the Current Warm Period, which occurs at the very end of the Korean temperature record.

What it means
The first important implication of Park's findings is the fact that they imply that "the various late-Holocene climate shifts all occurred in the Korean peninsula at the same time as in other regions of the world." The second important implication is that modern-day warming on the Korean peninsula is only slightly greater than what occurred there back in the Medieval Warm Period. And if one looks a little further back in Park's temperature reconstruction, it can be seen that approximately 2200 years ago it may actually have been slightly warmer than it was near the end of the 20th century AD, suggesting that there is nothing incredibly unusual or unnatural about the earth's current level of warmth.

References
Chang, C.-H. and Kim, C.-M. 1982. Late-Quaternary vegetation in the lake of Korea. Korean Journal of Botany 25: 37-53.

Chang, N.-K., Kim, Y.-P., O, I.-H. and Son, Y.-H. 1987. Past vegetation of Moor in Mt. Daeam in terms of the pollen analysis. Korean Journal of Ecology 10: 195-204.

Fujiki, T. and Yasuda, Y. 2004. Vegetation history during the Holocene from Lake Hyangho, northeastern Korea. Quaternary International 123-125: 63-69.

Jo, W.-R. 1979. Palynological studies on postglacial age in eastern coastal region, Korean peninsula. Tohoku-Chiri 31: 23-55.

Yoon, S.-O., Moon, Y.-R. and Hwang, S. 2008. Pollen analysis from the Holocene sediments of Lake Gyeongpo, Korea and its environmental implications. Journal of the Geological Society of Korea 44: 781-794.