A study is made of the effect of ground temperature variations with time and depth on the accuracy of thermoluminescence (TL) dating methods based on the shape of glow curves. It is shown that for accurate dating, detailed information is needed on the variation of temperature with time at the depth at which the object being dated was found. As a result of uncertainties in the temperature of the sample's immediate environment, errors well in excess of 10% in its age may be expected. This makes these methods rather inaccurate for use in archaeological dating but possibly of use in authenticity testing.