A Two-Thousand-Year Temperature History of the Extra-Tropical Northern Hemisphere
Ljungqvist, F.C. 2010. A new reconstruction of temperature variability in the extra-tropical Northern Hemisphere during the last two millennia. Geografiska Annaler Series A 92: 339-351.
The results of the Swedish scientist's stellar efforts are depicted in the following figure.
Figure 1. Reconstructed extra-tropical (30-90°N) mean decadal temperature variations relative to the 1961-1990 mean of the variance-adjusted 30-90°N CRUTEM3+HadSST2 instrumental temperature data of Brohan et al.(2006) and Rayner et al. (2006). Adapted from Ljungqvist (2010).
In discussing this temperature history, Ljungqvist states that it depicts "a Roman Warm Period c. AD 1-300, a Dark Age Cold Period c. AD 300-800, a Medieval Warm Period c. AD 800-1300 and a Little Ice Age c. AD 1300-1900, followed by the twentieth-century warming." These alternating warm/cold periods, in his words, "probably represent the much discussed quasi-cyclical c. 1470 ± 500-year Bond Cycles (Bond and Lotti, 1995; O'Brien et al., 1995; Bond et al., 1997, 2001; Oppo, 1997)," which "affected both Scandinavia and northwest North America synchronically (Denton and Karlen, 1973)" and have "subsequently also been observed in China (Hong et al., 2009a,b), the mid-latitude North Pacific (Isono et al., 2009) and in North America (Viau et al., 2006), and have been shown to very likely have affected the whole Northern Hemisphere during the Holocene (Butikofer, 2007; Wanner et al., 2008; Wanner and Butikofer, 2008), or even been global (Mayewski et al., 2004)."
Ljungqvist also notes that "decadal mean temperatures in the extra-tropical Northern Hemisphere seem to have equaled or exceeded the AD 1961-1990 mean temperature level during much of the Roman Warm Period and the Medieval Warm Period," and he says that "the second century, during the Roman Warm Period, is the warmest century during the last two millennia," while adding that "the highest average temperatures in the reconstruction are encountered in the mid to late tenth century," which was during the Medieval Warm Period. He warns, however, that the temperature of the last two decades "is possibly higher than during any previous time in the past two millennia," but adds that "this is only seen in the instrumental temperature data and not in the multi-proxy reconstruction itself," which is akin to saying that this possibility only presents itself if one applies Michael Mann's "Nature trick" of comparing "apples and oranges," which is clearly not valid.
This new study of Ljungqvist is especially important in that it utilizes, in his words, "a larger number of proxy records than most previous reconstructions," and that it "substantiates an already established history of long-term temperature variability." All of these facts, taken together, clearly demonstrate that there is nothing unusual, nothing unnatural or nothing unprecedented about the planet's current level of warmth, seeing it was just as warm as, or even warmer than, it has been recently during both the Roman and Medieval Warm Periods, when the atmosphere's CO2 concentration was more than 100 ppm less than it is today. And this latter observation, together with the realization that earth's climate naturally transits back and forth between cooler and warmer conditions on a millennial timescale, demonstrates that there is absolutely no need to associate the planet's current level of warmth with its current higher atmospheric CO2 concentration, in clear contradiction of the worn-out IPCC and climate-alarmist claim that the only way to explain earth's current warmth is to associate it with the greenhouse effect of CO2. That claim -- for which there is no supporting evidence, other than misplaced blind faith in climate models -- is totally bogus.
Brohan, P., Kennedy, J., Haris, I., Tett, S.F.B. and Jones, P.D. 2006. Uncertainty estimates in regional and global observed temperature changes: a new dataset from 1850. Journal of Geophysical Research 111: 10.1029/2005JD006548.
Bond, G. and Lotti, R. 1995. Iceberg discharges into the North Atlantic on millennial time scales during the last glaciation. Science 267: 1005-1010.
Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M.N., Showers, W., Hoffmann, S., Lotti-Bond, R., Hajdas, I. and Bonani, G. 2001. Persistent solar influence on North Atlantic climate during the Holocene. Science 294: 2130-2136.
Bond, G., Showers, W., Cheseby, M., Lotti, R., Almasi, P., deMenocal, P., Priore, P., Cullen, H., Hajdas, I. and Bonani, G. 1997. A pervasive millennial-scale cycle in North Atlantic Holocene and Glacial climate. Science 278: 1257-1266.
Butikofer, J. 2007. Millennial Scale Climate Variability During the Last 6000 Years -- Tracking Down the Bond Cycles. Diploma thesis, University of Bern, Bern, Switzerland.
Denton, G.H. and Karlen, W. 1973. Holocene climatic variations -- their pattern and possible cause. Quaternary Research 3: 155-205.
Hong, Y.T., Hong, B., Lin, Q.H., Shibata, Y., Zhu, Y.X., Leng, X.T. and Wang, Y. 2009a. Synchronous climate anomalies in the western North Pacific and North Atlantic regions during the last 14,000 years. Quaternary Science Reviews 28: 840-849.
Hong, B., Liu, C., Lin, Q., Yasuyuki, S., Leng, X., Wang, Y., Zhu, Y. and Hong, Y. 2009b. Temperature evolution from the δ18O record of Hami peat, Northeast China, in the last 14,000 years. Science in China Series D: Earth Sciences 52: 952-964.
Isono, D., Yamamoto, M., Irino, T., Oba, T., Murayama, M., Nakamura, T. and Kawahata, H. 2009. The 1500-year climate oscillation in the mid-latitude North Pacific during the Holocene. Geology 37: 591-594.
Loehle, C. 2009. A mathematical analysis of the divergence problem in dendroclimatology. Climatic Change 94: 233-245.
Mayewski, P.A., Rohling, E.E., Stager, J.C., Karlen, W., Maasch, K.A., Meeker, L.D., Meyerson, E.A., Gasse, F., van Kreveld, S., Holmgren, K., Lee-Thorp, J., Rosqvist, G. Rack, F., Staubwasser, M., Schneider, R.R. and Steig, E.J. 2004. Holocene climate variability. Quaternary Research 62: 243-255.
O'Brien, S.R., Mayewski, P.A., Meeker, L.D., Meese, D.A., Twickler, M.S. and Whitlow, S.E. 1995. Complexity of Holocene climate as reconstructed from a Greenland ice core. Science 270: 1962-1964.
Oppo, D. 1997. Millennial climate oscillations. Science 278: 1244-1246.
Rayner, N.A., Brohan, P., Parker, D.E., Folland, C.K., Kennedy, J.J., Vanicek, M., Ansell, T. and Tett, S.F.B. 2006. Improved analyses of changes and uncertainties in marine temperature measured in situ since the mid-nineteenth century: the HadSST2 dataset. Journal of Climate 19: 446-469.
Viau, A.E., Gajewski, K., Sawada, M.C. and Fines, P. 2006. Millennial-scale temperature variations in North America during the Holocene. Journal of Geophysical Research 111: 10.1029/2005JD006031.
Wanner, H. and Butikofer, J. 2008. Holocene Bond cycles: real or imaginary? Geografie-Sbornik CGS 113: 338-350.
Wanner, H., Beer, J., Butikofer, J., Crowley, T., Cubasch, U., Fluckiger, J., Goosse, H., Grosjean, M., Joos, F., Kaplan, J.O., Kuttel, M., Muller, S., Pentice, C., Solomina, O., Stocker, T., Tarasov, P., Wagner, M. and Widmann, M. 2008. Mid to late Holocene climate change -- an overview. Quaternary Science Reviews 27: 1791-1828.