Die kalte Sonne, Fritz Vahrenholt, Chemist, Sebastian Luening, Paleogeologist: Pre-industrial temperatures have undergone marked natural variations at every possible time-scale. Definition of an 1850–1900 “pre-industrial” reference level is therefore simplistic and does not do justice to the significant natural dynamics of the pre-industrial temperature development. Unfortunately, key reports on the climate limits refer to the pre-industrial temperature as if it had been static during past millennia.