Background
The author writes that "there is growing evidence that past changes in the thickness of ice covering volcanoes have affected their eruptive activity," stating that "the rate of volcanic activity in Iceland accelerated by a factor of 30-50 following the last deglaciation at approximately 12 ka (Maclennan et al., 2002)," while noting that "analyses of local and global eruption databases have identified a statistically significant correlation between periods of climatic warming associated with recession of ice and an increase in the frequency of eruptions (Jellinek et al., 2004; Nowell et al., 2006; Huybers and Langmuir, 2009)." Thus, he asks the next logical question: "Will the current ice recession provoke increased volcanic activity and lead to increased exposure to volcanic hazards?"

What was done
In response to his self-interrogation, Tuffen -- a researcher at the Lancaster Environment Centre of Lancaster University in the United Kingdom -- proceeds to "analyze our current knowledge of how ice thickness variations influence volcanism" and to "identify several unresolved issues that currently prevent quantitative assessment of whether activity is likely to accelerate in the coming century."

What was learned
At the conclusion of his review and analysis, Tuffen finds that "ice unloading may encourage more explosive eruptions," but that "melting of ice and snow may decrease the likelihood and magnitude of meltwater floods." On the other hand, he says there is (1) "uncertainty about the time scale of volcanic responses to ice unloading," (2) "poor constraint on how ice bodies on volcanoes will respond to twenty-first century climate change," (3) "lack of data on how past changes in ice thickness have affected the style of volcanic eruptions and associated hazards," and that (4) "the sensitivity of volcanoes to small changes in ice thickness or to recession of small glaciers on their flanks is unknown," (5) "it is not known how localized ice withdrawal from stratovolcanoes [tall, conical volcanoes with many layers (strata) of hardened lava, tephra, and volcanic ash] will affect shallow crustal magma storage and eruption," and (6) "broader feedbacks between volcanism and climate change remain poorly understood."

What it means
The UK researcher concludes that "in order to resolve these problems, both new data and improved models are required." In the data area, he states that "existing databases of known volcanic eruptions need to be augmented by numerous detailed case studies of the Quaternary eruptive history of ice-covered volcanoes," while in the area of models, he writes that "improved physical models are required to test how magma generation, storage and eruption at stratovolcanoes are affected by stress perturbations related to the waxing and waning of small-volume ice bodies on what is commonly steep topography." Last of all, he suggests that "feedbacks between the mass balance of ice sheets and glaciers and volcanic activity need to be incorporated into future earth-system models."

Hence, it is clear that much is known; but it is equally clear that much is still to be learned.

References
Huybers, P. and Langmuir, C. 2009. Feedback between deglaciation, volcanism, and atmospheric CO2. Earth and Planetary Science Letters 286: 479-491.

Jellinek, A.M., Manga, M. and Saar, M.O. 2004. Did melting glaciers cause volcanic eruptions in eastern California? Probing the mechanics of dike formation. Journal of Geophysical Research 109: 10.1029/2004JB002978.

Maclennan, J., Jull, M., McKenzie, D.P., Slater, L. and Gronvold, K. 2002. The link between volcanism and deglaciation in Iceland. Geochemistry, Geophysics, Geosystems 3: 10.1029/2001GC000282.

Nowell, D., Jones, C. and Pyle, D. 2006. Episodic quaternary volcanism in France and Germany. Journal of Quaternary Science 21: 645-675.