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

The paper by Martín-Chivelet et al. (2011) presents a temperature reconstruction for the past 4000 yr based on the δ13C 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 δ13C 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 δ13C 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 δ13C signal explaining the lack of correlation with other palaeotemperature compilation records. Therefore, a palaeotemperature reconstruction from these samples is thought to be unreliable.