What was done
The authors developed a 300-year record of hydrologic discharge events from Lake Tuborg on northern Ellesmere Island based on measurements of sediment lamination (varve) thickness, comparing their results with the melt records of the nearby Agassiz and Devon Island Ice Caps.

What was learned
Among a number of other things learned, Smith et al. remark that "of particular interest is the correspondence of melt peaks in the Agassiz Ice Cap and Devon Island Ice Cap ice core records with anomalously thick [Tuborg Lake] varves, following the mid-19th century."  Of even greater interest -- to us, at least -- is the fact that both ice cap melt records begin to rise from an 1845 starting point, for this observation identifies 1845 as the beginning of the end of the Little Ice Age and the start of the gradual temperature increase that has produced the Modern Warm Period.  As additional evidence for this conclusion, Smith et al. note that "several other studies indicate that the Arctic experienced a pronounced warming trend from the mid-19th century until the mid to late 20th century (Jacoby and D'Arrigo, 1989; Lamoureux and Bradley, 1996; Overpeck et al., 1997; Hughen et al., 2000) as the Arctic emerged from the 'Little Ice Age'."

What it means
These observations strike another blow for truth in the fierce debate that rages over the validity or invalidity of the IPCC-endorsed "hockeystick" temperature history of Mann et al. (1998, 1999), which is promoted by climate alarmists as proof of the need to curtail anthropogenic CO2 emissions; for whereas Mann et al.'s representation of the Northern Hemispheric warming that brought an end to the Little Ice Age does not begin until after 1910, the ice cap melt records of Koerner (1977) [Devon Island] and Koerner and Fisher (1990) [Agassiz] -- as well as the studies cited by Smith et al. (see above) -- demonstrate that it began a full 65 years earlier throughout much of the Arctic and other high northern latitudes, well before there had been any significant increase in the air's CO2 content due to man's industrial activities.  Hence, nearly half of the Little Ice Age-to-Modern Warm Period transition had to have had a natural non-anthropogenic origin, which leaves little reason to assign any of the latter portion of the transition to the effects of man either.

References
Hughen, K., Overpeck, J.T. and Anderson, R.F.  2000.  Recent warming in a 500-year palaeotemperature record from varved sediments, Upper Soper Lake, Baffin Island, Canada.  The Holocene 10: 9-19.

Jacoby, G.C. and D'Arrigo, R.D.  1989.  Reconstructed northern hemisphere annual temperature since 1671 based on high-latitude tree-ring data from North America.  Climatic Change 1: 39-59.

Koerner, R.M.  1977.  Devon Island ice cap; core stratigraphy and paleoclimate.  Science 196: 15-18.

Koerner, R.M. and Fisher, D.A.  1990.  A record of Holocene summer climate from a Canadian High-Arctic ice core.  Nature 343: 630-631.

Lamoureux, S.F. and Bradley, R.S.  1996.  A 3300 year varved sediment record of environmental change from northern Ellesmere Island, Canada.  Journal of Paleolimnology 10: 239-255.

Mann, M.E., Bradley, R.S. and Hughes, M.K.  1998.  Global-scale temperature patterns and climate forcing over the past six centuries.  Nature 392: 779-787.

Mann, M.E., Bradley, R.S. and Hughes, M.K.  1999.  Northern Hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations.  Geophysical Research Letters 26: 759-762.

Overpeck, J., Hughen, K., Hardy, D., Bradley, R., Case, R., Douglas, M., Finney, B., Gajewski, K., Jacoby, G., Jennings, A., Lamoureux, S., Lasca, A., MacDonald, G., Moore, J., Retelle, M., Smith, S., Wolfe, A. and Zielinski, G.  1997.  Arctic environmental change of the last four centuries.  Science 278: 1251-1256.