Thursday, November 8, 2012

New papers showing the Medieval Warming Period was warmer than the present

Re-posted from the latest NIPCC Report, two new papers add to hundreds of others showing that the Medieval Warming Period [MWP] was warmer than the Current Warm Period, "which makes it extremely difficult to believe that Earth's current level of warmth largely owes its existence to anthropogenic CO2 emissions, as the world's climate alarmists continue to claim it does."

The late Medieval Warm Period in Switzerland's Seebergsee

Larocque-Tobler, I., Stewart, M.M., Quinlan, R., Trachsel, M., Kamenik, C. and Grosjean, M. 2012. A last millennium temperature reconstruction using chironomids preserved in sediments of anoxic Seebergsee (Switzerland): consensus at local, regional and Central European scales. Quaternary Science Reviews 41: 49-56.

In presenting the rationale for their study, Larocque-Tobler et al. (2012) rhetorically ask: "Does the amplitude of climate change of the last century exceed the natural variability?" And in describing the first step in answering this question for themselves, they state that "high-temporally resolved paleo-climate reconstructions are needed to place the last century into a broader spatial and temporal context," which they thus proceed to do.

Working at Seebergsee (46°37'N, 7°28'E) - a small two-basin lake of surface area 0.06 km2 in the northern Swiss Alps - Larocque-Tobler et al. extracted a 3-m sediment core from the lake's deepest point back in AD 2005, which they scrutinized for head capsules of various chironomid species at near-annual resolution over the upper 36 cm of the core and at approximately decadal resolution throughout the rest of the core. These species assemblage data were then calibrated against instrumental temperature data from the closest meteorological station and compared with regional instrumental records stretching as far back as AD 1760, after which the result was used to reconstruct mean July air temperatures for the period AD 1073-2005.

In describing their findings the six scientists were careful to note that the temperature reconstruction they derived "starts at the end of the previously defined 'Medieval Climate Anomaly'," or MCA. This fact is very important, for it suggests that their temperature reconstruction may not include the warmest temperatures of the MCA. Not needing to do so, however, they state in the conclusion section of their report that even with their highly-truncated temperature record, "the MCA period has been shown to be warmer than the last century by about 1.2°C." However, they hasten to add that "the temperatures of the last century increased by 0.8°C," but following - in the very same sentence - they state that even with this increase, the latest temperatures of their record "did not exceed the MCA chironomid-inferred temperatures."

Once again, another carefully conducted study strongly suggests that the peak warmth of the Medieval Warm Period was likely significantly greater than that of the Current Warm Period has been to date.

The Medieval Warm Period in Northeast China

Wang, L., Rioual, P., Panizzo, V.N., Lu, H., Gu, Z., Chu, G., Yang, D., Han, J., Liu, J. and Mackay, A.W. 2012. A 1000-yr record of environmental change in NE China indicated by diatom assemblages from maar lake Erlongwan. Quaternary Research 78: 24-34.

In an initial explanation about why they did what they did, Wang et al. (2012) write that "lakes are excellent sensors of environmental change," and that "lake sediments can provide well-resolved records of change on different time scales," while noting that "crater and maar lakes are especially sensitive to climate change because typically they have a small catchment area and limited inflow/outflow." Moreover, they say such lakes "often provide high-resolution records due to limnological processes favorable to the development and preservation of seasonally laminated sediments," citing Zolitschka et al. (2000) in this regard. And they add that "diatoms are excellent indicators of environmental conditions and have been widely used to reconstruct Holocene climate variability," citing Smol and Cumming (2000), Battarbee et al. (2001) and Mackay et al. (2003).
Focusing on Lake Erlongwan, one of eight maar lakes in the Long Gang Volcanic Field of Jilin Province, NE China (42°18'N, 126°21'E) - which they describe as a closed dimictic lake that occupies an area of 0.3 km2 and has a small catchment (0.4 km2) with no natural inflows or outflow - Wang et al. retrieved a 66.5-cm-long sediment core from its central, deepest region in 2001, which they dated with the help of radiometric 210Pb, 137Cs and 14C analyses, and which they analyzed for diatom species and quantities. Although they note, in this regard, that diatoms "are generally not known to be very sensitive to water temperature," they indicate that "climate affects the physical properties of the lake water column, especially as it controls the seasonal durations of ice cover, water column mixing and stratification, which all have profound effects on the availability of nutrients and light necessary for algal photosynthesis and growth," so that "climate has an indirect influence on the composition and productivity of phytoplankton, especially non-motile organisms such as diatoms," which thus allows them to undertake "a detailed qualitative paleolimnological interpretation of the Lake Erlongwan sediment sequence based mainly on the growing body of literature that focuses on the ecology of planktonic diatoms, especially their responses to climate-driven changes in limnology."

The ten researchers report that "three intervals were identified by their diatom assemblages and correspond within dating uncertainties to the Medieval Warm Period, the Little Ice Age and the 20th century warming trend." During the MWP, they further indicate that "the duration of the summer was longer while the spring and autumn were shorter than the 20th century." And they unequivocally declare that "the period between ca. AD 1150 and 1200 was the warmest interval of the past 1000 years."

In view of the fact that, prior to the time of their study, there was no record of mean annual temperatures from NE China covering the past 1000 years with the same resolution as their diatom record, Wang et al.'s work demonstrates - for yet another part of the planet - that late-20th-century warmth, even with the help of an extra 100 ppm of CO2, was less than that of the MWP, which makes it extremely difficult to believe that Earth's current level of warmth largely owes its existence to anthropogenic CO2 emissions, as the world's climate alarmists continue to claim it does.

Additional References

Battarbee, R.W., Jones, V.J., Flower, B.P., Cameron, N.G., Bennion, H., Carvalho, L. and Juggins, S. 2001. Diatoms. In: Smol, J.P., Birks, H.J.B. and Last, W.M. (Eds.). Tracking Environmental Change Using Lake Sediments. Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 155-201.

Mackay, A.W., Jones, V.J. and Battarbee, R.W. 2003. Approaches to Holocene climate reconstruction using diatoms. In: Mackay, A.W., Battarbee, R.W., Birks, H.J.B. and Oldfield, F. (Eds.). Global Change in the Holocene. Arnold, London, United Kingdom, pp. 294-309.

Smol, J.P. and Cumming, B.F. 2000. Tracking long-term changes in climate using algal indicators in lake sediments. Journal of Phycology 36: 986-1011.

Zolitschka, B., Brauer, A., Negendank, J.F.W., Stockhausen, H. and Lang, A. 2000. Annually dated late Weichselian continental paleoclimate record from the Eifel, Germany. Geology 28: 783-786.

1 comment:

  1. Whether or not the MWP was slightly warmer than the present, it still marks a maximum in a ~1,000 year natural cycle. I estimate that the trend of that cycle was increasing at about 0.06 K/decade around the year 1900, but only about 0.05 K/decade in recent years. It may take another 100 to 200 years before it gets down to a rate of increase of zero at the long term maximum, and that would be of the order of 1,000 years since the peak of the MWP.

    So it does not surprise me that the MWP may have been warmer than at present, given that we may not yet be at the maximum. Our coming maximum will probably be less than a degree above the present trend line. But the maxima don't have to be the same anyway, because there could be a much longer natural cycle also affecting these maxima.