Papers supporting Medieval Warming Period from peer reviewed journals: Reference Hemer, M.A. and Harris, P.T. 2003. Sediment core from beneath the Amery Ice Shelf, East Antarctica, suggests mid-Holocene ice-shelf retreat. Geology 31: 127-130. Description Changes in the location of the edge of the Amery Ice Shelf were inferred from measurements of biogenic opal, absolute diatom abundance and the abundance of Fragilariopsis curta found in sediments retrieved from beneath the ice shelf at a point that is currently 80 km from land's edge. The MWP at ca. 750 14C yr BP was likely warmer than at any time during the CWP. Eastern Bransfield Basin, Antarctic Peninsula Reference Khim, B.-K., Yoon, H.I., Kang, C.Y. and Bahk, J.J. 2002. Unstable climate oscillations during the Late Holocene in the Eastern Bransfield Basin, Antarctic Peninsula. Quaternary Research 58: 234-245. Description General climatic features were inferred from a study of the grain size, total organic carbon content, biogenic silica content and, most importantly, magnetic susceptibility of 210Pb- and 14C-dated sediments retrieved from the eastern Bransfield Basin (61°58.9'S, 55°57.4'W) just off the northern tip of the Antarctic Peninsula. Most of the Medieval Warm Period (AD 1050-1550) was warmer than the Current Warm Period. Reference Noon, P.E., Leng, M.J. and Jones, V.J. 2003. Oxygen-isotope (δ18O) evidence of Holocene hydrological changes at Signy Island, maritime Antarctica. The Holocene 13: 251-263. Description Primarily summer climatic conditions were inferred from a δ18O record preserved in authigenic carbonate retrieved from sediments of Sombre Lake (60°43'S, 45°38'W) on Signy Island, maritime Antarctica. The Medieval Warm Period (AD 1130-1215) was warmer than the Current Warm Period. Reference Castellano, E., Becagli, S., Hansson, M., Hutterli, M., Petit, J.R., Rampino, M.R., Severi, M., Steffensen, J.P., Traversi, R. and Udisti, R. 2005. Holocene volcanic history as recorded in the sulfate stratigraphy of the European Project for Ice Coring in Antarctica Dome C (EDC96) ice core. Journal of Geophysical Research 110: Do6114, doi:10.1029/2004JD005259. Description The authors analyzed sulfate ice core stratigraphy from Dome C, Antarctica (75.10°S, 123.40°E) to obtain a record of Holocene volcanic eruptions, which they compared with other volcanic indices throughout Antarctica. Sulfate depositional fluxes of individual volcanic events were found to vary greatly among the different sites, which variation was attributed to changes in atmospheric circulation driven by climate forcing; and the team of ten researchers concluded that "changes in the extent and intra-Antarctic variability of volcanic depositional fluxes may have been consequences of the establishment of a Medieval Warming-like period that lasted [from about 1000] until about 1500 AD." Reference Holmgren, K., Tyson, P.D., Moberg, A. and Svanered, O. 2001. A preliminary 3000-year regional temperature reconstruction for South Africa. South African Journal of Science 97: 49-51. Description Maximum annual air temperatures in the vicinity of Cold Air Cave (24°1'S, 29°11'E) in the Makapansgat Valley of South Africa were inferred from a relationship between color variations in banded growth-layer laminations of a well-dated stalagmite and the air temperature of a surrounding 49-station climatological network developed over the period 1981-1995, as well as a quasi-decadal-resolution record of oxygen and carbon stable isotopes (MWP: AD 800-1100): Peak warmth of the Medieval Warm Period was as much as 2.5°C warmer than the Current Warm Period (AD 1961-1990 mean). Reference Giraudi, C. 2005. Middle to Late Holocene glacial variations, periglacial processes and alluvial sedimentation on the higher Apennine massifs (Italy). Quaternary Research 64: 176-184. Description Based on current relationships between elevation and soil periglacial and glacial processes, Giraudi estimated that the mean annual temperature on higher Apennine massifs in Italy (42°23'N, 13°31'E) from approximately AD 700 to 1030 were "higher than at present," and that winter temperatures were "at least 0.9°C higher" than those of today. Reference Liu, Z., Henderson, A.C.G. and Huang, Y. 2006. Alkenone-based reconstruction of late-Holocene surface temperature and salinity changes in Lake Qinghai, China. Geophysical Research Letters 33: 10.1029/2006GL026151. Description The authors developed a quantitative reconstruction of temperature changes over the past 3500 years based on alkenone distribution patterns in a sediment core retrieved from China's Lake Qinghai (37°N, 100°E), based on the alkenone unsaturation index that has been calibrated to the growth temperature of marine alkenone producers and "to temperature changes in lacustrine settings on a regional scale." This work revealed that the peak warmth of the Medieval Warm Period (AD 900-1500) exceeded the temperature of the latter part of the 20th century by about 0.5°C. Reference Wilson, A.T., Hendy, C.H. and Reynolds, C.P. 1979. Short-term climate change and New Zealand temperatures during the last millennium. Nature 279: 315-317. Description Temperatures derived from an 18O/16O profile through a stalagmite found in a New Zealand cave (40.67°S, 172.43°E) revealed the Medieval Warm Period to have occurred between AD 1050 and 1400 and to have been 0.75°C warmer than the Current Warm Period. Reference Cronin, T.M., Dwyer, G.S., Kamiya, T., Schwede, S. and Willard, D.A. 2003. Medieval Warm Period, Little Ice Age and 20th century temperature variability from Chesapeake Bay. Global and Planetary Change 36: 17-29. Description Using the magnesium/calcium (Mg/Ca) proxy method as a paleothermometer, the authors reconstructed a 2200-year record of spring sea surface temperature from four sediment cores taken from Chesapeake Bay (~38.89°N, 76.40°W). Statistical analyses revealed mean 20th-century temperatures were 0.15°C cooler than mean temperatures during the first stage of the Medieval Warm Period, which they delineate as occurring between 450 and 900 AD. Reference D'Arrigo, R., Wilson, R. and Jacoby, G. 2006. On the long-term context for late twentieth century warming. Journal of Geophysical Research 111: 10.1029/2005JD006352. Description D'Arrigo et al. (2006) assembled mostly tree-ring width (but some density) data from living and subfossil wood of coniferous tree species found at 66 high-elevation and latitudinal treeline North American and Eurasian sites, after which they analyzed the data via the Regional Curve Standardization detrending technique to reconstruct a history of annual temperature for the Northern Hemisphere between 20 and 90°N for the period AD 713-1995. In comparing the temperatures of the Medieval Warm Period (MWP, 950-1100 A.D.) with those of the Current Warm Period (CWP), based on the six longest chronologies they analyzed, they concluded that "the recent period does not look particularly warmer compared to the MWP." However, the mean of the six series did depict a warmer CWP; but they describe this relationship as "a bias/artifact in the full RCS reconstruction where the MWP, because it is expressed at different times in the six long records, is 'averaged out' (i.e., flattened) compared to the recent period which shows a much more globally consistent signal." Nevertheless, the data are what they are; and for the period covered only by the proxy data (so that "apples and oranges" are not compared), they found that peak twentieth century warmth (which occurred between 1937 and 1946) exceeded peak MWP warmth by 0.29°C. Reference Bjorck, S., Rittenour, T., Rosen, P., Franca, Z., Moller, P., Snowball, I., Wastegard, S., Bennike, O. and Kromer, B. 2006. A Holocene lacustrine record in the central North Atlantic: proxies for volcanic activity, short-term NAO mode variability, and long-term precipitation changes. Quaternary Science Reviews 25: 9-32. Description General climatic conditions were inferred from "sedimentology, geochemistry, diatom analyses, magnetic properties, and multivariate statistics, together with 14C and 210Pb dating techniques" applied to a core obtained from the center of a small crater lake on the Azores island of Pico (38°26'N, 28°12'W). The MWP was broadly characterized by the adjoining "cooler/drier periods" of 400-800 and 1300-1800 cal yr BP, but was said by the authors to be most strongly expressed between AD 1000 and 1100, which is where we have located it. Reference Rein B., Lückge, A., Reinhardt, L., Sirocko, F., Wolf, A. and Dullo, W.-C. 2005. El Niño variability off Peru during the last 20,000 years. Paleoceanography 20: 10.1029/2004PA001099. Description The authors derived sea surface temperatures from alkenones extracted from a high-resolution marine sediment core retrieved off the coast of Peru (12.05°S, 77.66°W), spanning the past 20,000 years and ending in the 1960s. From their Figure 11, adapted below, it can be seen that the warmest temperatures of this 20,000 year period (~23.2°C) occurred during the late Medieval time (AD 800-1250). Taking this value, 23.2°C, and comparing it with the modern monthly long-term means in sea surface temperature, which the authors characterize as between 15°C and 22°C, we estimate the peak warmth of the Medieval Warm Period for this region was about 1.2°C above that of the Current Warm Period.