In an important study that appeared in the Proceedings of the U.S. National Academy of Sciences, Hu et al. (2001) "conducted multiproxy geochemical analyses of a sediment core from Farewell Lake in the northwestern foothills of the Alaska Range," obtaining what they describe as "the first high-resolution quantitative record of Alaskan climate variations that spans the last two millennia."  Their results, in their words, "suggest that at Farewell Lake SWT [surface water temperature] was as warm as the present at AD 0-300 [during the Roman Warm Period], after which it decreased steadily by ~3.5°C to reach a minimum at AD 600 [during the depths of the Dark Ages Cold Period]."  From that point in time, they say "SWT increased by ~3.0°C during the period AD 600-850 and then [during the Medieval Warm Period] exhibited fluctuations of 0.5-1.0°C until AD 1200."  Completing their narrative, they say that "between AD 1200-1700, SWT decreased gradually by 1.25°C [as the world descended into the depths of the Little Ice Age], and from AD 1700 to the present, SWT increased by 1.75C," the latter portion of which warming initiated the Modern Warm Period.

In commenting on their findings, Hu et al. remark that "the warmth before AD 300 at Farewell Lake coincides with a warm episode extensively documented in northern Europe ... whereas the AD 600 cooling is coeval with the European 'Dark Ages'."  They also say that "the relatively warm climate AD 850-1200 at Farewell Lake corresponds to the Medieval Climatic Anomaly, a time of marked climatic departure over much of the planet."  And they say that "these concurrent changes suggest large-scale teleconnections in natural climatic variability during the last two millennia, likely driven by atmospheric controls."

Noting that "20th-century climate is a major societal concern in the context of greenhouse warming," Hu et al. conclude by reiterating that their record "reveals three time intervals of comparable warmth: AD 0-300, 850-1200, and post-1800," and they say that "these data agree with tree-ring evidence from Fennoscandia, indicating that the recent warmth is not atypical of the past 1000 years," in unmistakable contradiction of those who claim that it is.

Carbotte et al. (2004) located fossil oyster beds within the Tappan Zee area of the Hudson River estuary (New York, USA) via chirp sub-bottom and side-scan sonar surveys, after which they retrieved sediment cores from the sites that provided shells for radiocarbon dating.  They report that oysters flourished in this area during the mid-Holocene warm period, when "summertime temperatures were 2-4°C warmer than today (e.g., Webb et al., 1993; Ganopolski et al., 1998)."  Thereafter, they found that the oysters "disappeared with the onset of cooler climate at 4,000-5,000 cal. years BP," but that they "returned during warmer conditions of the late Holocene," which they identify as the Roman and Medieval Warm Periods as delineated by Keigwin (1996) and McDermott et al. (2001), explicitly stating that "these warmer periods coincide with the return of oysters in the Tappan Zee."  Unfortunately, they report that their shell dates suggest a final "major demise at ~500-900 years BP," which timing they describe as being "consistent with the onset of the Little Ice Age," noting further that within nearby Chesapeake Bay, "Cronin et al. (2003) report a sustained period of cooler springtime water temperatures (by ~2-5°C) during the Little Ice Age relative to the earlier Medieval Warm Period."  Last of all, they add that "similar aged fluctuations in oyster presence are observed within shell middens elsewhere along the Atlantic seaboard," citing results obtained from Maine to Florida.

In addition to its higher temperatures, the Roman Warm Period in North America was in many places accompanied by drier conditions. Willard et al. (2003), for example, "examine[d] the late Holocene (2300 yr BP to present) record of Chesapeake Bay and the adjacent terrestrial ecosystem in its watershed through the study of fossil dinoflagellate cysts and pollen from sediment cores."  They found that "several dry periods ranging from decades to centuries in duration are evident in Chesapeake Bay records."  The first of these periods of lower-than-average precipitation, which spanned the period 200 BC-AD 300, occurred during the latter part of the Roman Warm Period, while the next such period (~AD 800-1200) "corresponds to the 'Medieval Warm Period', which has been documented as drier than average by tree-ring (Stahle and Cleaveland, 1994) and pollen (Willard et al., 2001) records from the southeastern USA."  They also note that droughts "in the 'Medieval Warm Period' and between ~AD 50 and AD 350 spanning a century or more have been indicated by Great Plains tree-ring (Stahle et al., 1985; Stahle and Cleaveland, 1994), lacustrine diatom and ostracode (Fritz et al., 2000; Laird et al., 1996a, 1996b) and detrital clastic records (Dean, 1997)."

Much the same has been found to be the case for Alberta, Canada, where Campbell (2002) analyzed the grain sizes of sediment cores obtained from Pine Lake (52°N, 113.5°W) to provide a high-resolution record of climate variability for this part of the continent over the past 4000 years.  This effort revealed periods of both increasing and decreasing grain size (moisture availability) throughout the record at decadal, centennial and millennial time scales.  The most prominent departures included several-centuries-long epochs that corresponded to the Little Ice Age (about AD 1500-1900), Medieval Warm Period (about AD 700-1300), Dark Ages Cold Period (about BC 100 to AD 700) and Roman Warm Period (about BC 900-100).  In addition, a standardized median grain-size history revealed that the highest rates of stream discharge during the past 4000 years occurred during the Little Ice Age at about 300-350 years ago.  During this time, grain sizes were about 2.5 standard deviations above the 4000-year mean.  In contrast, the lowest rates of streamflow were observed around AD 1100, when median grain sizes were nearly 2 standard deviations below the 4000-year mean.

In reviewing the results of these several studies, it is clear that the Roman Warm Period was a very real phenomenon throughout North America, manifesting itself in both warmer temperatures and drier moisture conditions in different parts of the continent.

References
Campbell, C.  2002.  Late Holocene lake sedimentology and climate change in southern Alberta, Canada.  Quaternary Research 49: 96-101.

Carbotte, S.M., Bell, R.E., Ryan, W.B.F., McHugh, C., Slagle, A., Nitsche, F. and Rubenstone, J.  2004.  Environmental change and oyster colonization within the Hudson River estuary linked to Holocene climate.  Geo-Marine Letters 24: 212-224.

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.

Dean, W.E.  1997.  Rates, timing, and cyclicity of Holocene eolian activity in north-central United States: evidence from varved lake sediments.  Geology 25: 331-334.

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Keigwin, L.D.  1996.  The Little Ice Age and Medieval Warm Period in the Sargasso Sea.  Science 274: 1504-1508.

Laird, K.R., Fritz, S.C., Grimm, E.C. and Mueller, P.G.  1996a.  Century-scale paleoclimatic reconstruction from Moon Lake, a closed-basin lake in the northern Great Plains.  Limnology and Oceanography 41: 890-902.

Laird, K.R., Fritz, S.C., Maasch, K.A. and Cumming, B.F.  1996b.  Greater drought intensity and frequency before AD 1200 in the Northern Great Plains, USA.  Nature 384: 552-554.

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