Ice-wedge casts as indicators of palaeotemperatures: precise proxy or wishful thinking?

The use of ice-wedge casts to reconstruct palaeotemperatures involves three stringent assumptions: (1) the influence of air temperature on ice-wedge cracking and the distribution of growing ice wedges are well known in contemporary permafrost environments; (2) contemporary and former permafrost environments are sufficiently similar for the same quantitative relationships between air temperature and ice-wedge cracking to apply to both environments; and (3) the history of ice-wedge growth and decay can confidently be inferred from ice-wedge casts. We propose that the validity of these assumptions has been overestimated in terms of the Weichselian of northwest Europe because of (i) limited knowledge of the frequency of ice-wedge cracking in contemporary permafrost environments; (ii) the complex and incompletely understood natural controls on cracking; (iii) probable differences between former cold environments in mid latitudes and contemporary cold environments in high latitudes; (iv) limited understanding of ice-wedge growth and decay histories, and of the natural controls on and mechanisms of ice-wedge casting; and (v) different time perspectives. Given all these uncertainties, it is timely to critically re-evaluate the use of Weichselian ice-wedge casts for palaeoclimatic and environmental reconstructions.