The Case for a Global Medieval Warm Period Grows Ever Stronger

This goes along way to removing any lingering doubt in regard to the reality of the MWP.  I am not so quick yet to link these events directly to what is surely a minute change in solar radiation.  To start with, we have been unable to convince ourselves that we can presently measure such a variation and it is supposed to be happening now.

The expanding coldness of the Southern Hemisphere is also a powerful counterargument.

On top of all that it has become clear to me that the present day Arctic has been warming up through the addition of incremental heat from the Gulf Stream for the past thirty or more years.  This heat by itself is not a huge increment but it now arrives every year and is progressively eroding the Arctic sea ice.

It is why I loudly proclaimed in 2007 that we will have largely clear Arctic waters as soon as 2012.

This means though that the Arctic sea itself will begin to accumulate heat far more efficiently thereafter.  It will develop a longer season that will optimize its effect of the climate of the Northern Hemisphere.  The conditions we associate with the MWP will fully return and remain stable for several centuries.

What is particularly startling is just how modest a change is needed to bring on what is a major and generally beneficial climate change.  We never detected the heat flow change in the Gulf Stream at all yet it surely happened.  A warmer Arctic will allow the Gulf Stream itself to also warm up over time by a degree or so and slowly approach the temperature regime of the Bronze Age.

The important lesson is that a single incremental change in heat flow in the Gulf Stream has brought n this major climate event and is continuing to implement it.

As an aside, three year go, Gavin Menzies argued for a Chinese navigation of the Arctic from the Atlantic through to the Bering Strait.  This was an obvious impossibility.  Yet the time frame was just as the MWP was ending in 1422 AD.  It is no longer impossibility at all and we can now predict such wide open seas in the near term and their continuance for centuries.

The remaining ice this year is already too little to oppose such seamanship and two or three more years of this will make it routine.

The Case for a Global Medieval Warm Period Grows Ever Stronger


Hong, B., Liu, C.-Q., Lin, Q.-H., Yasuyuki, S., Leng, X.-T., Wang, Y., Zhu, Y.-X. and Hong, Y.-T. 2009. Temperature evolution from the δ18O record of Hani peat, Northeast China, in the last 14000 years. Science in China Series D: Earth Sciences 
52: 952-964.


Of the Medieval Warm Period (MWP), the authors write that "because it is a distinct warm period nearest to the modern warming period and happened before the Industrial Revolution, it naturally becomes a [source of] comparison with modern warming." And in this regard, they add that "a universal concern in academic circles is [1] whether it also existed outside the European region and [2] whether it is a common phenomenon."

What was done

In a study designed to broach both questions, the authors extracted cores of peat from a location close to Hani Village, Liuhe County, Jilin Province, China (42°13'N, 126°31'E); and they used them to develop, as they describe it, "a peat cellulose δ18O temperature proxy record proximately existing for 14,000 years."

What was learned

Their efforts revealed, first of all, that the MWP had indeed held sway on the Chinese mainland over the period AD 700-1400, peaking at about AD 900. And the eight researchers report that phenological data from east China (Ge et al., 2006) and tree-ring records from west China (Yang et al., 2000) also indicate that "the temperature on the Chinese mainland was distinctly warmer during the MWP." In fact, they say MWP temperatures were as much as "0.9-1.0°C higher than modern temperatures (Zhang, 1994)."

Secondly, with respect to the last 14,000 years, Hong et al. write that "sudden cooling events, such as the Older Dryas, Inter-Allerod, Younger Dryas, and nine ice-rafted debris events of the North Atlantic" -- which are described by Stuiveret al. (1995) and Bond et al. (1997, 2001) -- "are almost entirely reiterated in the temperature signals of Hani peat cellulose δ18O." And they state that "these cooling events show that the repeatedly occurring temperature cooling [and warming] pattern not only appeared in the North Atlantic Region in the high latitudes, but also in the Northwest Pacific Region in the middle latitudes," indicating that the recurring warming and cooling did indeed occur "outside the European region" and that it truly was "a common phenomenon."

Last of all, we note that the earlier paper of Hong et al. (2000) -- which describes a 6,000-year peat cellulose δ18O record derived from nearby Jinchuan Town, Huinan County, Jilin Province, China (42°20'N, 126°22'E) -- identified δ18O periodicities of 86, 93, 101, 110, 127, 132, 140, 155, 207, 245, 311, 590, 820 and 1046 years, which they say "are similar to those detected in solar excursions," and which they consider "further evidence for a close relationship between solar activity and climate variations on timescales of decades to centuries." These findings were highly praised by Fairbridge (2001), who noted that "almost identical equivalents are seen in solar emission periodicities and their harmonics, e.g., 86.884 years = 40 x 2.172 year Quasi Biennial Oscillation (QBO) as well as in the lunar tidal/apsides beat frequency (17.3769 years) which also matches closely with most of the longer spectral peaks, e.g., 140 (139) years, 207 (208.5), 311 (312.8), 590 (590.8) and 1046 (1042.6) years." And for these spectacular spectral findings, Fairbridge wrote that "Hong et al. deserve the appreciation of the entire Holocene community."

What it means

As ever more pertinent work is conducted, the case for a global and solar-induced Medieval Warm Period grows ever stronger, as it also does for all of the similar warm periods that preceded it over the prior 13,000 years, which makes the case for a similar origin for the Current Warm Period ever more likely as well.


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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.
Fairbridge, R.W. 2001. Six millennia in Chinese peats, relating to planetary-solar-luniterrestrial periodicities: a comment on Hong, Jiang, Liu, Zhou, Beer, Li, Leng, Hong and Qin. The Holocene 11: 121-122.
Ge, Q.S., Zheng, J.Y. and Liu, J. 2006. Amplitude and rhythm of winter half-year temperature change in eastern China for the past 2000 years. Advances in Climate Change Research 2: 108-112.
Hong, Y.T., Jiang, H.B., Liu, T.S., Zhou, L.P., Beer, J., Li, H.E., Leng, X.T., Hong, B. and Qin, X.G. 2000. Response of climate to solar forcing recorded in a 6000-year δ18O time-series of Chinese peat cellulose. The Holocene 10: 1-7.
Stuiver, M., Grootes, P.M. and Braziunas, T.F. 1995. The GISP2 δ18O climate record of the past 16,500 years and the role of the sun, ocean, and volcanoes. Quaternary Research 44: 341-354.
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Zhang, D.E. 1994. Evidence for the existence of the Medieval Warm Period in ChinaClimatic Change 26: 293-297.
Reviewed 15 September 2010 

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