What was done
The authors review the principles of ¹⁴C wiggle-match dating, its limitations, and the insights it has provided about the timing and possible causes of climate change during the Holocene.

What was learned
Mauquoy et al. report that "analyses of microfossils and macrofossils from raised peat bogs by Kilian et al. (1995), van Geel et al. (1996), Speranza et al. (2000), Speranza (2000) and Mauquoy et al. (2002a, 2002b) have shown that climatic deteriorations [to cooler and wetter conditions] occurred during periods of transition from low to high delta ¹⁴C (the relative deviation of the measured ¹⁴C activity from the standard after correction for isotope fractionation and radioactive decay; Stuiver and Polach, 1977)."  This close correspondence, in their words, suggests that "changes in solar activity may well have driven these changes during the Bronze Age/Iron Age transition around c. 850 cal. BC (discussed in detail by van Geel et al., 1996, 1998, 1999, 2000) and the 'Little Ice Age' series of palaeoclimatic changes."  The observed changes in solar activity at these points in time, however, have typically been rather small, forcing Mauquoy et al. to conclude that "some amplification mechanism must operate to cause the reconstructed abrupt climatic changes."

The European scientists suggest two possibilities for this solar-amplifying mechanism: (1) "increased cosmic ray intensity, stimulating cloud formation and precipitation (Svensmark and FriisChristensen, 1997)," and (2) "reduced solar UV intensity, causing a decline of stratospheric ozone production and cooling as a result of less absorption of sunlight (Haigh, 1996, 2001)."  Noting that "modeling results of Shindell et al. (2001) suggest solar-induced variations of ozone production could drive temperature changes in the middle and lower atmospheres, which in turn could cause changes in the North Atlantic Oscillation and the Arctic Oscillation," they tentatively conclude that the solar UV mechanism may be the more likely of the two.

What it means
There is little doubt that some effect(s) of solar variability is(are) responsible for the climatic variability that is evident in palaeoclimatic studies of the Holocene; however, more research is needed to conclusively identify the specific amplifying mechanism(s) by which the climatic changes were brought to pass.

References
Haigh, J.D.  1996.  The impact of solar variability on climate.  Science 272: 981-984.

Haigh, J.D.  2001.  Climate variability and the influence of the sun.  Science 294: 2109-2111.

Kilian, M.R., van der Plicht, J. and van Geel, B.  1995.  Dating raised bogs: new aspects of AMS ¹⁴C wiggle matching, a reservoir effect and climatic change.  Quaternary Science Reviews 14: 959-966.

Mauquoy, D., Engelkes, T., Groot, M.H.M., Markesteijn, F., Oudejans, M.G., van der Plicht, J. and van Geel, B.  2002a.  High resolution records of late Holocene climate change and carbon accumulation in two north-west European ombrotrophic peat bogs.  Palaeogeography, Palaeoclimatology, Palaeoecology 186: 275-310.

Mauquoy, D., van Geel, B., Blaauw, M. and van der Plicht, J.  2002b.  Evidence from North-West European bogs shows 'Little Ice Age' climatic changes driven by changes in solar activity.  The Holocene 12: 1-6.

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.

Speranza, A.  2000.  Solar and Anthropogenic Forcing of Late-Holocene Vegetation Changes in the Czech Giant Mountains.  PhD thesis.  University of Amsterdam, Amsterdam, The Netherlands.

Speranza, A.O.M., van der Plicht, J. and van Geel, B.  2000.  Improving the time control of the Subboreal/Subatlantic transition in a Czech peat sequence by ¹⁴C wiggle-matching.  Quaternary Science Reviews 19: 1589-1604.

Stuiver, M. and Polach, H.A.  1977.  Discussion: reporting ¹⁴C data.  Radiocarbon 19: 355-363.

Svensmark, H. and Friis-Christensen, E.  1997.  Variation of cosmic ray flux and global cloud coverage - a missing link in solar-climate relationships.  Journal of Atmospheric and Solar-Terrestrial Physics 59: 1225-1232.

van Geel, B., Buurman, J. and Waterbolk, H.T.  1996.  Archaeological and palaeoecological indications of an abrupt climate change in the Netherlands and evidence for climatological teleconnections around 2650 BP.  Journal of Quaternary Science 11: 451-460.

van Geel, B., Heusser, C.J., Renssen, H. and Schuurmans, C.J.E.  2000.  Climatic change in Chile at around 2700 BP and global evidence for solar forcing: a hypothesis.  The Holocene 10: 659-664.

van Geel, B., Raspopov, O.M., Renssen, H., van der Plicht, J., Dergachev, V.A. and Meijer, H.A.J.  1999.  The role of solar forcing upon climate change.  Quaternary Science Reviews 18: 331-338.

van Geel, B., van der Plicht, J., Kilian, M.R., Klaver, E.R., Kouwenberg, J.H.M., Renssen, H., Reynaud-Farrera, I. and Waterbolk, H.T.  1998.  The sharp rise of delta ¹⁴C c. 800 cal BC: possible causes, related climatic teleconnections and the impact on human environments.  Radiocarbon 40: 535-550.