By using concepts from dynamical systems theory, we demonstrate a technique which has the potential to distinguish explicitly between internally forced and externally forced climate variability. This technique is applied to the instrumental Central England Temperature (CET) record, where variability related to changes in the (external) solar activity and variability due to (internal) climate dynamics are separated. Based on the CET record and the sunspot record, we reconstruct a map relating successive summer temperature maxima given the number of sunspots. For low values of the sunspot number, the equilibrium behavior of this map shows chaotic motion, indicating dominant internal climate dynamics, for high values of the sunspot number this is not the case. The robustness of the reconstruction is tested using surrogate data. ¿ 2001 American Geophysical Union