A New-and-Improved 1200-Year Temperature History of the Gulf of Alaska
Wiles, G.C., D'Arrigo, R.D., Barclay, D., Wilson, R.S., Jarvis, S.K., Vargo, L. and Frank, D. 2014. Surface air temperature variability reconstructed with tree rings for the Gulf of Alaska over the past 1200 years. The Holocene 24: 198-208.
The work of the seven scientists revealed a number of centennial trends that included "a warm interval centered on AD 950 for coastal Alaska that occurred around the time of the Medieval Warm Period," and which "for the first time," as they describe it, "includes a divergence-free view of contemporary warming that is ongoing and is comparable to the MWP." But from the graph of their results, it can be seen that the peak warmth of the MWP was actually slightly greater than the peak warmth of the Current Warm Period (CWP).
In addition to this important finding, Wiles et al. determined that their tree-ring reconstruction "supports centennial modes of solar forcing as a driver of surface air temperatures in the Gulf of Alaska, with lunar tidal, solar variability, internal variability, and volcanism impacting climate on annual to decadal timescales." More specifically, they write that "the observed 220-year and 170-year modes are consistent with both the glacial records (Wiles et al., 2004) and the De Vries cycle, indicating that solar variability is a major climate driver at the century timescale," while they add that "Little Ice Age coolings are fairly coherent across southern Alaska and the Yukon with the coolest intervals corresponding to the Sporer and Maunder [solar] minima."
In considering all of the above, nothing in this study suggests there is anything unusual, unnatural or unprecedented about the Current Warm Period, in that temperatures slightly warmer than those of recent times occurred a full millennium ago, when there was way less CO2 in the atmosphere than there is currently, which in turn suggests that the much greater CO2 concentrations of today need not be the cause of Earth's current - and not unusual - level of warmth.
D'Arrigo, R.D., Wilson, R., Liepert, B. and Cherubini, P. 2008. On the 'Divergence Problem' in northern forests: A review of the tree-ring evidence and possible causes. Global and Planetary Change 60: 289-305.
Driscoll, W., Wiles, G.C., D'Arrigo, R.D. and Wilmking, M. 2005. Divergent tree growth response to recent climatic warming, Lake Clark National Park and Preserve, Alaska. Geophysical Research Letters 32: 10.1029/2005GL024258.
Wiles, G.C., D'Arrigo, R.D., Villalba, R., Calkin, P.E. and Barclay, D.J. 2004. Century-scale solar variability and Alaskan temperature change over the past millennium. Geophysical Research Letters 31: 10.1029/2004GL020050.
Wilson, R., D'Arrigo, R., Buckley, B., Buntgen, U., Esper, J., Frank, D., Luckman, B., Payette, S., Vose, R. and Youngblut, D. 2007. A matter of divergence - Tracing recent warming at hemispheric scales using tree-ring data. Journal of Geophysical Research: Atmospheres 112: 1.1029/2006JD008318.