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A New Temperature History (AD 674-2010) of Southeast Finland

Paper Reviewed
Helama, S., Vartiainen, M., Holopainen, J., Makela, H.M., Kolstrom, T. and Merilainen, J. 2014. A palaeotemperature record for the Finnish Lakeland based on microdensitometric variations in tree rings. Geochronometria 41: 265-277.

In a study published in the journal Geochronometria, Helama et al. (2014) describe how they created, calibrated and verified a continuous dendroclimatic record of the summer temperatures of southeast Finland that spanned the period from AD 674 to 2010, based on X-ray-derived tree-ring maximum latewood density (MXD) measurements made on subfossil and modern pine (Pinus sylvesris) materials.

This record, in their words, depicts "multi-centennial warmth spanning from the 9th to the 12th century," and they say that the long-term cooling observed since Medieval times until the end of the 19th century was similar to what has been observed in MXD and multi-proxy records of northern Fennoscandia, citing Esper et al. (2012) and Helama et al. (2010), as well as what has been observed throughout the entire Northern Hemisphere, citing Mann et al. (1999). And they add that the warmest 250-year periods in the reconstructions of Esper et al. and Helama et al. occurred from AD 816-1065 and AD 932-1181, respectively, during what they refer to as the Medieval Climate Anomaly. In addition, they say this warmth appears to be "coeval to a number of proxy-based hemispheric climate records that show evidence concerning the relatively warm conditions during the same centuries," citing Ljungqvist et al. (2012).

Subsequently, the six Finnish scientists report that a "concentration of markedly cool periods was recorded from the 17th to the early 20th century," coeval with "the wide-spread climatic cooling between AD 1570 and 1900 when Northern Hemisphere summer temperatures fell significantly below their recent (AD 1961-1990) mean level," citing Matthews and Briffa (2005). They also note, in this regard, that the coolest temperatures they recorded during this "Little Ice Age" were from the years between AD 1704 and 1753. And this interval, in their words, "was synchronous with, albeit slightly post-dating, the period of the Maunder Minimum (AD 1645 to 1715," as per Eddy (1976), and especially so with the late Maunder Minimum (AD 1675-1715) that has been denoted "the climax of the Little Ice Age in Europe," as per Luterbacher et al. (2001).

Writing further about this Little Ice Age climax, Helama et al. say it was a period "during which the overall activity of the Sun was drastically reduced and sunspots virtually disappeared," citing Hoyt and Schatten (1998). And they note that cooling in this region could have been expected "approximately two decades after the solar irradiance decreases," due to "inertia in the oceanic response and shift towards the negative phase in the atmospheric oscillations pattern over the North Atlantic and European land areas," citing Shindell et al. (2001).

Taken in their entirety, these several observations clearly reveal the natural, and possibly solar-induced, warming and cooling and warming again that produced Earth's Medieval Warm Period, Little Ice Age and Current Warm Period, which phenomenon demonstrates that there is nothing unusual, unnatural or unprecedented about the Earth's current level of flat-lining warmth.

Eddy, J.A. 1976. The Maunder Minimum. Science 192: 1189-1202.

Esper, J.,Frank, D.C., Timonen, M., Zorita, E., Wilson, R.J.S., Luterbacher, J., Holzkamper, S., Fischer, N., Wagner, S., Nievergelt, D., Verstege, A. and Buntgen, U. 2012. Orbital forcing of tree-ring data. Nature Climate Change 2: 862-866.

Helama, S., Macias Fauria, M., Mielikanen, K., Timonen, M. and Eronen, M. 2010. Sub-Milankovitch solar forcing of past climates: mid and late Holocene perspectives. Geological Society of America Bulletin 122: 1981-1988.

Hoyt, D.V. and Schatten, K.H. 1998. Group sunspot numbers: A new solar activity reconstruction. Solar Physics 179: 189-219.

Ljungqvist, F.C., Krusic, P.J., Brattstrom, G. and Sundqvist, H.S. 2012. Northern Hemisphere temperature patterns in the last 12 centuries. Climate of the Past 8: 227-249.

Luterbacher, J., Rickli, R., Xoplaki, E., Tinguely, C., Beck, C., Pfister, C. and Wanner, H. 2001. The Late Maunder Minimum (1675-1715) - A key period for studying decadal scale climatic change in Europe. Climatic Change 49: 441-462.

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

Matthews, J.A. and Briffa, K.R. 2005. The 'Little Ice Age'; Reevaluation of an evolving concept. Grografiska Annaler 87A: 17-36.

Shindell, D.T., Schmidt, G.A., Mann, M.E., Rind, D. and Waple, A. 2001. Solar forcing of regional climate change during the maunder Minimum. Science 294: 2149-2152.

Posted 5 November 2014