Comment on Land surface temperature changes in Northern Iberia since 4000 yr BP, based on δ13C of speleothems

The paper by Martin-Chivelet et al. (2011) presents a temperature reconstruction for the past 4000 yr based on the delta C-13 record of three speleothems from different caves in northern Spain. I consider that the record of these speleothems cannot provide a reliable temperature reconstruction due to the lack of: (1) an adequate calibration (2) a mechanism able to explain the observed delta C-13 signal variability in terms of surface air temperature (SAT) and (3) a clear correlation when the record is quantitatively compared with other thermal reconstructions. Instead, the delta C-13 signal in these speleothems responds to a series of factors and not a single control. Some of these controls are known to be affected by factors other than SAT and could dominate the delta C-13 signal explaining the lack of correlation with other palaeotemperature compilation records. Therefore, a palaeotemperature reconstruction from these samples is thought to be unreliable. (C) 2012 Elsevier B.V. All rights reserved.