Dr. Johannes Koch

   Department of Geography

   Kwantlen Polytechnic University

 

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RESEARCH ON CLIMATE FORCINGS

This research tries to establish what climate forcings can explain glacier behaviour throughout the Holocene and in more detail the past millennium. The most common climate forcings are changes in Earth's orbit leading to changes in insolation, changes in solar radiation, mostly due to changes in sunspot activity, ocean-atmosphere interactions, such as El Niño/Southern Oscillation, volcanic eruptions, and changes in greenhouse gases.

 

Forcing of Holocene glacial history

We evaluate the hypothesis, made by previous researchers, that there is a relation between Holocene sunspot activity and alpine glacier fluctuations. Major Holocene glacier advances in western Canada occurred during the periods 7700-7400, 6400-5100, 4400-3900, 3800-2000, 2000-1100 14C years BP, and during the last millennium. The advances are broadly synchronous with those in other mountainous areas in the Northern Hemisphere, as well as those in the Southern Hemisphere. Periods of glacier advance in both hemispheres correlate with times of low sunspot activity. The relative extents of glacier advances in the two hemispheres, however, are different. Glaciers in the Northern Hemisphere were most extensive in the late Holocene, whereas those in the Southern Hemisphere were most extensive in the early Holocene. These differences can be explained by changes in solar insolation in the two hemispheres over the course of the Holocene. During the early Holocene solar insolation was low (high) in the Southern (Northern) Hemisphere, consistent with the greater extent of glaciers in the south than in the north. In contrast, during the late Holocene solar insolation was high (low) in the Southern (Northern) Hemisphere, again consistent with the difference in extent of glaciers in the two regions.

Figure 2.1 Glacier fluctuations in western Canada and reconstructed decadal sunspot numbers (Solanki et al. , 2004) during the Holocene. The red line represents relative glacier extent through time (top is present extent; bottom is maximum Holocene extent). The blue line shows decadal sunspot numbers, and the orange line (bottom) is an 11-point smoothed reconstruction of sunspot numbers. The blue vertical bars indicate periods of global glacier advance. The negative reconstructed sunspot values are an artefact introduced by uncertainties in the reconstruction (Solanki et al. , 2004).
Figure 2.2 Patterns of Holocene glacier fluctuations in the Cordilleras of North and South America, which are considered representative of the two hemispheres, and summer insolation at 60 0 N and S after Bradley et al. (2002). The vertical blue bars indicate periods of global glacier advance.

Koch, J., and Clague, J.J., 2006. Are insolation and sunspot activity the primary drivers of global Holocene glacier fluctuations? PAGES Newsletter, 14(3): 20- 21. (download paper 0.4 Mb)

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Forcing of Little Ice Age glacial history

The similarity in the timing and extent of glacier fluctuations in western North America, Scandinavia, the European Alps, South America, and New Zealand suggest global forcing. Comparing the combined global glacial record with Northern Hemisphere temperature reconstructions shows that the two are in broad agreement. Periods of glacier advance and recession are broadly synchronous with relatively cold and warm periods, respectively. Furthermore, comparing the timing of glacier fluctuations in the past millennium with the record of solar activity during the past millennium and with reconstructed sunspot numbers indicate that glacier advances and times of moraine construction appear to coincide with sunspot minima, specifically the Oort (AD 1020-1080), Wolfe (AD 1290-1370), Spörer (AD 1460-1550), Maunder (AD 1645-1715), and Dalton (ca. AD 1795-1825) minima. Thus, changes in solar radiation likely play an important role in late Holocene climate and glacier change.

Figure 2.3 Comparison of glacier advances in western North America over the past millennium and inferred solar irradiance (Solanki et al., 2004). Blue vertical bars denote intervals of sunspot minima (Stuiver, 1961; Bond et al., 2001).

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Forcing of Medieval time glacial history

The Medieval Warm Period is an interval of purportedly warm climate during the early part of the past millennium. The duration, areal extent, and even existence of the Medieval Warm Period have been debated; in some areas the climate of this interval appears to have been affected more by changes in precipitation than in temperature. Here, we summarize and present new evidence showing that several glaciers in western North America were advancing during Medieval time and that some glaciers achieved extents similar to those at the peak of the Little Ice Age, many hundred years later. The advances cannot be reconciled with a climate similar to that of the 20th century, which has been argued to be an analog, and likely were the result of increased winter precipitation due to prolonged La Niña-like conditions that, in turn, may be linked to elevated solar activity. Changes in solar output may initiate a response in the tropical Pacific that directly impacts the El Niño/Southern Oscillation and associated North Pacific teleconnections.

Figure 2.4 Comparison of glacier advances in western North America during Medieval time and early Little Ice Age, and inferred solar irradiance (Solanki et al., 2004). Blue vertical bars denote intervals of sunspot minima (Stuiver, 1961; Bond et al., 2001).

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Last modified: 20.05.2010